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A method is a block of code that performs a specific task.

Suppose you need to create a program to create a circle and color it. You can create two methods to solve this problem:

• a method to draw the circle
• a method to color the circle

Dividing a complex problem into smaller chunks makes your program easy to understand and reusable.

In Java, there are two types of methods:

• User-defined Methods : We can create our own method based on our requirements.
• Standard Library Methods : These are built-in methods in Java that are available to use.

Let's first learn about user-defined methods.

• Declaring a Java Method

The syntax to declare a method is:

• returnType - It specifies what type of value a method returns For example if a method has an int return type then it returns an integer value. If the method does not return a value, its return type is void .
• methodName - It is an identifier that is used to refer to the particular method in a program.
• method body - It includes the programming statements that are used to perform some tasks. The method body is enclosed inside the curly braces { } .

For example,

In the above example, the name of the method is adddNumbers() . And, the return type is int . We will learn more about return types later in this tutorial.

This is the simple syntax of declaring a method. However, the complete syntax of declaring a method is

• modifier - It defines access types whether the method is public, private, and so on. To learn more, visit Java Access Specifier .
• static - If we use the static keyword, it can be accessed without creating objects. For example, the sqrt() method of standard Math class is static. Hence, we can directly call Math.sqrt() without creating an instance of Math class.
• parameter1/parameter2 - These are values passed to a method. We can pass any number of arguments to a method.

Calling a Method in Java

In the above example, we have declared a method named addNumbers() . Now, to use the method, we need to call it.

Here's is how we can call the addNumbers() method.

Example 1: Java Methods

In the above example, we have created a method named addNumbers() . The method takes two parameters a and b . Notice the line,

Here, we have called the method by passing two arguments num1 and num2 . Since the method is returning some value, we have stored the value in the result variable.

Note : The method is not static. Hence, we are calling the method using the object of the class.

• Java Method Return Type

A Java method may or may not return a value to the function call. We use the return statement to return any value. For example,

Here, we are returning the variable sum . Since the return type of the function is int . The sum variable should be of int type. Otherwise, it will generate an error.

Example 2: Method Return Type

In the above program, we have created a method named square() . The method takes a number as its parameter and returns the square of the number.

Here, we have mentioned the return type of the method as int . Hence, the method should always return an integer value.

Note : If the method does not return any value, we use the void keyword as the return type of the method. For example,

Method Parameters in Java

A method parameter is a value accepted by the method. As mentioned earlier, a method can also have any number of parameters. For example,

If a method is created with parameters, we need to pass the corresponding values while calling the method. For example,

Example 3: Method Parameters

Here, the parameter of the method is int . Hence, if we pass any other data type instead of int , the compiler will throw an error. It is because Java is a strongly typed language.

Note : The argument 24 passed to the display2() method during the method call is called the actual argument.

The parameter num accepted by the method definition is known as a formal argument. We need to specify the type of formal arguments. And, the type of actual arguments and formal arguments should always match.

• Standard Library Methods

The standard library methods are built-in methods in Java that are readily available for use. These standard libraries come along with the Java Class Library (JCL) in a Java archive (*.jar) file with JVM and JRE.

• print() is a method of java.io.PrintSteam . The print("...") method prints the string inside quotation marks.
• sqrt() is a method of Math class. It returns the square root of a number.

Here's a working example:

Example 4: Java Standard Library Method

To learn more about standard library methods, visit Java Library Methods .

What are the advantages of using methods?

1. The main advantage is code reusability . We can write a method once, and use it multiple times. We do not have to rewrite the entire code each time. Think of it as, "write once, reuse multiple times".

Example 5: Java Method for Code Reusability

In the above program, we have created the method named getSquare() to calculate the square of a number. Here, the method is used to calculate the square of numbers less than 6 .

Hence, the same method is used again and again.

2. Methods make code more readable and easier to debug. Here, the getSquare() method keeps the code to compute the square in a block. Hence, makes it more readable.

Table of Contents

• Calling a Java Method
• Method Parameters
• Advantages of Java Methods

Sorry about that.

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Java Library

Methods in Java – Explained with Code Examples

Methods are essential for organizing Java projects, encouraging code reuse, and improving overall code structure.

In this article, we will look at what Java methods are and how they work, including their syntax, types, and examples.

Here's what we'll cover:

What are java methods.

• Types of Access Specifiers in Java – Public ( public ) – Private ( private ) – Protected ( protected ) – Default ( Package-Private )
• Types of Methods – Pre-defined vs. User-defined – Based on functionality

In Java, a method is a set of statements that perform a certain action and are declared within a class.

Here's the fundamental syntax for a Java method:

Let's break down the components:

• accessSpecifier : defines the visibility or accessibility of classes, methods, and fields within a program.
• returnType : the data type of the value that the method returns. If the method does not return any value, the void keyword is used.
• methodName : the name of the method, following Java naming conventions.
• parameter : input value that the method accepts. These are optional, and a method can have zero or more parameters. Each parameter is declared with its data type and a name.
• method body : the set of statements enclosed in curly braces {} that define the task the method performs.
• return statement : if the method has a return type other than void , it must include a return statement followed by the value to be returned.

Here's an example of a simple Java method:

In this example, the addNumbers method takes two integers as parameters ( a and b ), calculates their sum, and returns the result. The main method then calls this method and prints the result.

Compile the Java code using the terminal, using the javac command:

Methods facilitate code reusability by encapsulating functionality in a single block. You can call that block from different parts of your program, avoiding code duplication and promoting maintainability.

Types of Access Specifiers in Java

Access specifiers control the visibility and accessibility of class members (fields, methods, and nested classes).

There are typically four main types of access specifiers: public, private, protected, and default. They dictate where and how these members can be accessed, promoting encapsulation and modularity.

Public ( public )

This grants access to the member from anywhere in your program, regardless of package or class. It's suitable for widely used components like utility functions or constants.

In this example:

• The MyClass class is declared with the public modifier, making it accessible from any other class.
• The publicField is a public field that can be accessed from outside the class.
• The publicMethod() is a public method that can be called from outside the class.
• The main method is the entry point of the program, where an object of MyClass is created, and the public field and method are accessed.

Private ( private )

This confines access to the member within the class where it's declared. It protects sensitive data and enforces encapsulation.

• The MyClass class has a privateField and a privateMethod , both marked with the private modifier.
• The accessPrivateMembers() method is a public method that can be called from outside the class. It provides access to the private field and calls the private method.

Protected ( protected )

The protected access specifier is used to make members (fields and methods) accessible within the same package or by subclasses, regardless of the package. They are not accessible from unrelated classes. It facilitates inheritance while controlling access to specific members in subclasses.

• The Animal class has a protected field ( species ) and a protected method ( makeSound ).
• The Dog class is a subclass of Animal , and it can access the protected members from the superclass.
• The displayInfo() method in the Dog class accesses the protected field and calls the protected method.

With the protected access specifier, members are accessible within the same package and by subclasses, promoting a certain level of visibility and inheritance while still maintaining encapsulation.

Default ( Package-Private )

If no access specifier is used, the default access level is package-private . Members with default access are accessible within the same package, but not outside it. It's often used for utility classes or helper methods within a specific module.

• The Animal class does not have any access modifier specified, making it default (package-private). It has a package-private field species and a package-private method makeSound .
• The Dog class is in the same package as Animal , so it can access the default (package-private) members of the Animal class.
• The Main class runs the program by creating an object of Dog and calling its displayInfo method.

When you run this program, it should output the species and the sound of the animal.

How to Choose the Right Access Specifier

• Public: Use for widely used components, interfaces, and base classes.
• Private: Use for internal implementation details and sensitive data protection.
• Default: Use for helper methods or components specific to a package.
• Protected: Use for shared functionality among subclasses, while restricting access from outside the inheritance hierarchy.

Types of Methods

In Java, methods can be categorized in two main ways:

1. Predefined vs. User-defined:

Predefined methods: These methods are already defined in the Java Class Library and can be used directly without any declaration.

Examples include System.out.println() for printing to the console and Math.max() for finding the maximum of two numbers.

User-defined methods: These are methods that you write yourself to perform specific tasks within your program. They are defined within classes and are typically used to encapsulate functionality and improve code reusability.

• add is a user-defined method because it's created by the user (programmer).
• The method takes two parameters ( num1 and num2 ) and returns their sum.
• The main method calls the add method with specific values, demonstrating the customized functionality provided by the user.

2. Based on functionality:

Within user-defined methods, there are several other classifications based on their characteristics:

Instance Methods:

Associated with an instance of a class. They can access instance variables and are called on an object of the class.

Here are some key characteristics of instance methods:

Access to Instance Variables:

• Instance methods have access to instance variables (also known as fields or properties) of the class.
• They can manipulate the state of the object they belong to.

Use of this Keyword:

• Inside an instance method, the this keyword refers to the current instance of the class. It's often used to differentiate between instance variables and parameters with the same name.

Non-static Context:

• Instance methods are called in the context of an object. They can't be called without creating an instance of the class.

Declaration and Invocation:

• Instance methods are declared without the static keyword.
• They are invoked on an instance of the class using the dot ( . ) notation.

Here's a simple example in Java to illustrate instance methods:

• bark and ageOneYear are instance methods of the Dog class.
• They are invoked on instances of the Dog class ( myDog and anotherDog ).
• These methods can access and manipulate the instance variables ( name and age ) of the respective objects.

Instance methods are powerful because they allow you to encapsulate behavior related to an object's state and provide a way to interact with and modify that state.

Static Methods:

A static method belongs to the class rather than an instance of the class. This means you can call a static method without creating an instance (object) of the class. It's declared using the static keyword.

Static methods are commonly used for utility functions that don't depend on the state of an object. For example, methods for mathematical calculations, string manipulations, and so on.

Abstract Methods:

These methods are declared but not implemented in a class. They are meant to be overridden by subclasses, providing a blueprint for specific functionality that must be implemented in each subclass.

Abstract methods are useful when you want to define a template in a base class or interface, leaving the specific implementation to the subclasses. Abstract methods define a contract that the subclasses must follow.

Other method types: Additionally, there are less common types like constructors used for object initialization, accessor methods (getters) for retrieving object data, and mutator methods (setters) for modifying object data.

In this article, we will look at Java methods, including their syntax, types, and recommended practices.

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Assignment, Arithmetic, and Unary Operators

The simple assignment operator.

One of the most common operators that you'll encounter is the simple assignment operator " = ". You saw this operator in the Bicycle class; it assigns the value on its right to the operand on its left:

This operator can also be used on objects to assign object references , as discussed in Creating Objects .

The Arithmetic Operators

The Java programming language provides operators that perform addition, subtraction, multiplication, and division. There's a good chance you'll recognize them by their counterparts in basic mathematics. The only symbol that might look new to you is " % ", which divides one operand by another and returns the remainder as its result.

The following program, ArithmeticDemo , tests the arithmetic operators.

This program prints the following:

You can also combine the arithmetic operators with the simple assignment operator to create compound assignments . For example, x+=1; and x=x+1; both increment the value of x by 1.

The + operator can also be used for concatenating (joining) two strings together, as shown in the following ConcatDemo program:

By the end of this program, the variable thirdString contains "This is a concatenated string.", which gets printed to standard output.

The Unary Operators

The unary operators require only one operand; they perform various operations such as incrementing/decrementing a value by one, negating an expression, or inverting the value of a boolean.

The following program, UnaryDemo , tests the unary operators:

The increment/decrement operators can be applied before (prefix) or after (postfix) the operand. The code result++; and ++result; will both end in result being incremented by one. The only difference is that the prefix version ( ++result ) evaluates to the incremented value, whereas the postfix version ( result++ ) evaluates to the original value. If you are just performing a simple increment/decrement, it doesn't really matter which version you choose. But if you use this operator in part of a larger expression, the one that you choose may make a significant difference.

The following program, PrePostDemo , illustrates the prefix/postfix unary increment operator:

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Operators constitute the basic building block of any programming language. Java too provides many types of operators which can be used according to the need to perform various calculations and functions, be it logical, arithmetic, relational, etc. They are classified based on the functionality they provide.

Types of Operators: 

• Arithmetic Operators
• Unary Operators
• Assignment Operator
• Relational Operators
• Logical Operators
• Ternary Operator
• Bitwise Operators
• Shift Operators

This article explains all that one needs to know regarding Assignment Operators. 

Assignment Operators

These operators are used to assign values to a variable. The left side operand of the assignment operator is a variable, and the right side operand of the assignment operator is a value. The value on the right side must be of the same data type of the operand on the left side. Otherwise, the compiler will raise an error. This means that the assignment operators have right to left associativity, i.e., the value given on the right-hand side of the operator is assigned to the variable on the left. Therefore, the right-hand side value must be declared before using it or should be a constant. The general format of the assignment operator is, 

Types of Assignment Operators in Java

The Assignment Operator is generally of two types. They are:

1. Simple Assignment Operator: The Simple Assignment Operator is used with the “=” sign where the left side consists of the operand and the right side consists of a value. The value of the right side must be of the same data type that has been defined on the left side.

2. Compound Assignment Operator: The Compound Operator is used where +,-,*, and / is used along with the = operator.

Let’s look at each of the assignment operators and how they operate: 

1. (=) operator: 

This is the most straightforward assignment operator, which is used to assign the value on the right to the variable on the left. This is the basic definition of an assignment operator and how it functions. 

Syntax:  

Example:  

2. (+=) operator: 

This operator is a compound of ‘+’ and ‘=’ operators. It operates by adding the current value of the variable on the left to the value on the right and then assigning the result to the operand on the left. 

Note: The compound assignment operator in Java performs implicit type casting. Let’s consider a scenario where x is an int variable with a value of 5. int x = 5; If you want to add the double value 4.5 to the integer variable x and print its value, there are two methods to achieve this: Method 1: x = x + 4.5 Method 2: x += 4.5 As per the previous example, you might think both of them are equal. But in reality, Method 1 will throw a runtime error stating the “i ncompatible types: possible lossy conversion from double to int “, Method 2 will run without any error and prints 9 as output.

Reason for the Above Calculation

Method 1 will result in a runtime error stating “incompatible types: possible lossy conversion from double to int.” The reason is that the addition of an int and a double results in a double value. Assigning this double value back to the int variable x requires an explicit type casting because it may result in a loss of precision. Without the explicit cast, the compiler throws an error. Method 2 will run without any error and print the value 9 as output. The compound assignment operator += performs an implicit type conversion, also known as an automatic narrowing primitive conversion from double to int . It is equivalent to x = (int) (x + 4.5) , where the result of the addition is explicitly cast to an int . The fractional part of the double value is truncated, and the resulting int value is assigned back to x . It is advisable to use Method 2 ( x += 4.5 ) to avoid runtime errors and to obtain the desired output.

Same automatic narrowing primitive conversion is applicable for other compound assignment operators as well, including -= , *= , /= , and %= .

3. (-=) operator: 

This operator is a compound of ‘-‘ and ‘=’ operators. It operates by subtracting the variable’s value on the right from the current value of the variable on the left and then assigning the result to the operand on the left. 

4. (*=) operator:

 This operator is a compound of ‘*’ and ‘=’ operators. It operates by multiplying the current value of the variable on the left to the value on the right and then assigning the result to the operand on the left. 

5. (/=) operator: 

This operator is a compound of ‘/’ and ‘=’ operators. It operates by dividing the current value of the variable on the left by the value on the right and then assigning the quotient to the operand on the left. 

6. (%=) operator: 

This operator is a compound of ‘%’ and ‘=’ operators. It operates by dividing the current value of the variable on the left by the value on the right and then assigning the remainder to the operand on the left. 

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Java methods, java classes, java file handling, java how to, java reference, java examples, java operators.

Operators are used to perform operations on variables and values.

In the example below, we use the + operator to add together two values:

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Although the + operator is often used to add together two values, like in the example above, it can also be used to add together a variable and a value, or a variable and another variable:

Java divides the operators into the following groups:

• Arithmetic operators
• Assignment operators
• Comparison operators
• Logical operators
• Bitwise operators

Arithmetic Operators

Arithmetic operators are used to perform common mathematical operations.

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Java Assignment Operators

Assignment operators are used to assign values to variables.

In the example below, we use the assignment operator ( = ) to assign the value 10 to a variable called x :

The addition assignment operator ( += ) adds a value to a variable:

A list of all assignment operators:

Java Comparison Operators

Comparison operators are used to compare two values (or variables). This is important in programming, because it helps us to find answers and make decisions.

The return value of a comparison is either true or false . These values are known as Boolean values , and you will learn more about them in the Booleans and If..Else chapter.

In the following example, we use the greater than operator ( > ) to find out if 5 is greater than 3:

Java Logical Operators

You can also test for true or false values with logical operators.

Logical operators are used to determine the logic between variables or values:

Java Bitwise Operators

Bitwise operators are used to perform binary logic with the bits of an integer or long integer.

Note: The Bitwise examples above use 4-bit unsigned examples, but Java uses 32-bit signed integers and 64-bit signed long integers. Because of this, in Java, ~5 will not return 10. It will return -6. ~00000000000000000000000000000101 will return 11111111111111111111111111111010

In Java, 9 >> 1 will not return 12. It will return 4. 00000000000000000000000000001001 >> 1 will return 00000000000000000000000000000100

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Multiply 10 with 5 , and print the result.

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Java Assignment Operators

Java programming tutorial index.

The Java Assignment Operators are used when you want to assign a value to the expression. The assignment operator denoted by the single equal sign = .

In a Java assignment statement, any expression can be on the right side and the left side must be a variable name. For example, this does not mean that "a" is equal to "b", instead, it means assigning the value of 'b' to 'a'. It is as follows:

Java also has the facility of chain assignment operators, where we can specify a single value for multiple variables.

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Quiz yourself: Interface methods and assignment compatibility in Java

What does it mean when a method has no modifiers—and a semicolon instead of a body?

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Given these four Java types

What is the result? Choose one.

Answer. This question investigates the accessibility of interface methods, interface implementation, and assignment compatibility. For this quiz question, look at each of the types that are declared and observe the key characteristics of the sample code.

Starting with the Command interface, notice that the type declaration has no modifier. This gives the interface package-level access, which means that it is accessible only within the bot package.

Next, the execute method is declared with no modifiers and has a semicolon in place of a body. This is valid, and if a method is declared this way in an interface, it will be implicitly public and abstract. From this you can determine that the interface is accessible and valid; therefore, option B is incorrect.

The Engine class is public, so it is accessible anywhere in the same module (or in the same JVM if the code is running without modules). The class declares a single method called run. This method is public, so it’s also accessible anywhere. The method is also static, so no instances of Engine need to be created to use the method. The method takes a single argument of type Command. The Engine class is in the same package as the Command interface, so it is accessible. The body of the run method simply calls the execute method of the Command argument. Command declares that the method, and the usage (the argument type sequence, which is empty), is valid. Because there is no reason for this code to fail, you can determine that option C is incorrect.

Notice that the AboutCommand class is in a different package from the Command interface. In addition, although it has the word Command in its name, this class does not contain the code implements Command . There are two immediate conclusions that can be drawn from this.

• Because AboutCommand doesn’t reference Command, it’s not a problem that it’s in a different package.
• While AboutCommand is not assignment-compatible with Command, this does not cause a problem here. (It does have consequences in other code, however.)

Also notice that the execute method in AboutCommand has package access and would not be a valid override of the execute method in Command. This isn’t a problem, however, since this method does not attempt such an override.

From these observations, you can see the AboutCommand class compiles successfully and option E is incorrect.

Finally, look at the Main class. It’s in the package bot, so it has access to the Command type. It imports the public type bot.command.AboutCommand , so it has access to that too. The main method has a valid signature line, and that signature is consistent with a program entry point. However, the body of the method has a problem. The argument type for the Engine.run method must be assignment-compatible with Command. However, as noted earlier, AboutCommand does not implement Command; therefore, it is not assignment-compatible with that type. That means the code Engine.run(ac); will fail to compile and option D is correct.

Because the Main class does not compile, option A must be incorrect.

Conclusion. The correct answer is option D.

Related quizzes

• Quiz yourself: Using core functional interfaces: Predicate
• Quiz yourself: Default methods
• Quiz yourself: Abstract classes and default methods in Java
• Quiz yourself: Java abstract classes and access modifiers for abstract methods

Simon Roberts

Simon Roberts joined Sun Microsystems in time to teach Sun’s first Java classes in the UK. He created the Sun Certified Java Programmer and Sun Certified Java Developer exams. He wrote several Java certification guides and is currently a freelance educator who publishes recorded and live video training through Pearson InformIT (available direct and through the O’Reilly Safari Books Online service). He remains involved with Oracle’s Java certification projects.

Mikalai Zaikin

Mikalai Zaikin is a lead Java developer at IBA Lithuania (part of worldwide IBA Group) and currently located in Vilnius. During his career, Zaikin has helped Oracle with development of Java certification exams, and he has been a technical reviewer of several Java certification books, including three editions of the famous Sun Certified Programmer for Java study guides by Kathy Sierra and Bert Bates.

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Java 22 and IntelliJ IDEA

Java 22 is here, fully supported by IntelliJ IDEA 2024.1 , allowing you to use these features now!

Java 22 has something for all – from new developers to Java experts, features related to performance and security for big organizations to those who like working with bleeding edge technology, from additions to the Java language to improvements in the JVM platform, and more.

It is also great to see how all these Java features, release after release, work together to create more possibilities and have a bigger impact on how developers create their applications that address existing pain points, perform better and are more secure.

This blog post doesn’t include a comprehensive coverage of all the Java 22 features. If you are interested in that, I’d recommend you to check out this link to know everything about what’s new and changing in Java 22, including the bugs.

In this blog post, I’ll cover how IntelliJ IDEA helps you get started, up and running with some of the Java 22 features, such as, String Templates , Implicitly Declared Classes and Instance Main Methods , Statements before super() , and Unnamed variables and patterns .

Over the past month, I published separate blog posts to cover each of these topics in detail. If you are new to these topics, I’d highly recommend you check out those detailed blog posts (I’ve included their links in the relevant subsections in this blog post). In this blog post, I’ll cover some sections from those blog posts, especially how IntelliJ IDEA supports them. Let’s start by configuring IntelliJ IDEA to work with the Java 22 features.

IntelliJ IDEA Configuration

Java 22 support is available in IntelliJ IDEA 2024.1 Beta . The final version will release soon in March 2024.

In your Project Settings, set the SDK to Java 22. For the language level, select ‘22 (Preview) – Statements before super(), string templates (2nd preview etc.)’ on both the Project and Modules tab, as shown in the below settings screenshot:

If you do not have Java 22 downloaded to your system yet, don’t worry; IntelliJ IDEA has your back! You could use the same Project settings window, select ‘Download JDK’, after you click on the drop down next to SDK. You’ll see the below popup that would enable you to choose from a list of vendors (such as Oracle OpenJDK, GraalVM, Azul Zulu and others):

With the configuration under our belt, let’s get started with covering one of my favorite new features, that is, String Templates.

String Templates (Preview Language feature) The existing String concatenation options are difficult to work with and could be error prone; String templates offer a better alternative, that is, String interpolation with additional benefits such as validation, security and transformations via template processors.

Please check out my detailed blog post on this topic: String Templates in Java – why should you care? if you are new to this topic. It covers all the basics, including why you need String Templates, with multiple hands-on examples on built-in and user defined String processors.

IntelliJ IDEA can highlight code that could be replaced with String Templates Let’s assume you defined the following code to log a message that combines string literals and variable values using the concatenation operator:

The output from the preceding code could be an issue if you miss adding spaces in the String literals. The code isn’t quite easy to read or understand due to multiple opening and closing double quotes, that is, " and the + operator, and it would get worse if you add more literals, or variable values to it.

You could replace the preceding code with either StringBuilder.append() , String.format() or String.formatted() method or by using the class MessageFormat (as shown in my detailed blog post on this topic), but each of these methods have their own issues.

Don’t worry; IntelliJ IDEA could detect such code, suggest that you could replace it with String template, and do that for you, as shown below. It doesn’t matter if you are not even aware of the syntax of the String templates, IntelliJ IDEA has your back 🙂

Embedded expressions in String Templates and IntelliJ IDEA The syntax to embed a remplate expression (variable, expressible or a method call) is still new to what Java developers are used to and could be challenging to use without help. Don’t worry, IntelliJ IDEA has your back!

Each embedded expression must be enclosed within \{}. When you type \{, IntelliJ IDEA adds the closing ‘}’ for you. It also offers code completion to help you select a variable in scope, or any methods on it. If the code that you insert doesn’t compile, IntelliJ IDEA will highlight that too (as a compilation error), as shown in the following gif:

Using String Templates with Text Blocks Text blocks are quite helpful when working with string values that span multiple lines, such as, JSON, XML, HTML, SQL or other values that are usually processed by external environments. It is common for us Java developers to create such string values using a combination of string literals and variable values (variables, expressions or method calls).

The example below shows how IntelliJ IDEA could detect and create a text block using String templates for multiline string values that concatenates string literals with variable values. It also shows how IntelliJ IDEA provides code completion for variable names within such blocks. When you type in \{ , IntelliJ IDEA adds } . As you start typing the variable name countryName , it shows the available variables in that context:

Language injection and String Templates You could also inject a language or a reference in string values that spans single line or multiple lines, such as, a text block. By doing so, you get comprehensive coding assistance to edit the literal value. You could avail of this feature temporarily or permanently by using the @Language annotation, as shown below:

You can check out this link for detailed information on the benefits and usage of injecting language or reference in IntelliJ IDEA.

Predefined Template Processors With the String templates, you get access to predefined processors like the STR , FMT and RAW . I’d highly recommend you to check out my detailed blog post on String templates for multiple hands-on examples on it.

Custom Template Processor

Let’s work with a custom String template that isn’t covered in my previous blog post.

Imagine you’d like to create an instance of a record, say, WeatherData , that stores the details of the JSON we used in the previous section. Assume you define the following records to store this weather data represented by the JSON in the previous section:

You could create a method to return a custom String template that would process interpolated string, accept a class name ( WeatherData for this example) and return its instance:

Depending on the logic of your application, you might want to escape, delete or throw errors for the special characters that you encounter in the the JSON values interpolated via template expressions, as follows (the following method chooses to escape the special characters and include them as part of the JSON value):

You could initialize and use this custom JSON template processor as below. Note how elegant and concise the solution is with a combination of textblocks and String templates. The JSON is easy to read, write and understand (thanks to text blocks). The template expressions make it clear and obvious about the sections that are not constants and would be injected by the variables. At the end, the custom template processor WEATHER_JSON would ensure the resultant JSON is validated according to the logic you defined and returns an instance of WeatherData (doesn’t it sound magical?) :

Do not miss to check out my detailed blog post on this topic: String Templates in Java – why should you care? to discover how you could use the predefined String templates like FMT , to generate properly formatted receipts for, say, your neighborhood stationery store, or, say encode and decode combinations like :) or :( to emojis like 🙂 or ☹️. Does that sound fun to you?

Implicitly Declared Classes and Instance Main Methods (Preview language feature)

Introduced as a preview language feature in Java 21, this feature is in its second preview in Java 22.

It would revolutionize how new Java developers would get started learning Java. It simplifies the initial steps for students when they start learning basics, such as variable assignment, sequence, conditions and iteration. Students no longer need to declare an explicit class to develop their code, or write their main() method using this signature – public static void main(String []) . With this feature, classes could be declared implicitly and the main() method can be created with a shorter list of keywords.

If you are new to this feature, I’d highly recommend you to check out my detailed blog post: ‘HelloWorld’ and ‘main()’ meet minimalistic on this feature. In this blog post, I’ll include a few of the sections from it.

Class ‘HelloWorld’ before and after Java 21

Before Java 21, you would need to define a class, say, HelloWorld , that defined a main() method with a specific list of keywords, to print any text, say, ‘Hello World’ to the console, as follows:

With Java 21, this initial step has been shortened. You can define a source code file, say, HelloWorld.java, with the following code, to print a message to the console (it doesn’t need to define a class; it has a shorter signature for method main() ):

The preceding code is simpler than what was required earlier. Let’s see how this change could help you focus on what you need, rather than what you don’t.

Compiling and executing your code

Once you are done writing your code, the next step is to execute it.

On the command prompt, you could use the javac and java commands to compile and execute your code. Assuming you have defined your code in a source code file HelloWorld.java, you could use the following commands to run and execute it:

Since Java 11, it is possible to skip the compilation process for code defined in a single source code file, so you could use just the second command (by specifying the name of the source code file, as follows):

However, since instance main methods and implicit classes is a preview language feature, you should add the flag --enable-preview with --source 22 with these commands, as follows:

Sooner or later, you might switch to using an IDE to write your code. If you wish to use IntelliJ IDEA for creating instance main methods, here’s a quick list of steps to follow. Create a new Java project, select the build system as IntelliJ (so you could use Java compiler and runtime tools), create a new file, say, HelloWorld.java with your instance main method and set the properties to use Java 22, before you run your code, as shown in the following gif (It could save you from typing out the compilation/ execution commands on the command prompt each time you want to execute your code):

Are you wondering if it would be better to create a ‘Java class’ instead of a ‘File’ in the ‘src’ folder? The option of selecting a Java class would generate the body of a bare minimum class, say, public class HelloWorld { } . Since we are trying to avoid unnecessary keywords in the beginning, I recommended creating a new ‘File’ which wouldn’t include any code.

What else can main() do apart from printing messages to the console?

As included in my detailed post on this topic , I included multiple hand-on examples to show what you could achieve via just the main() method:

• Example 1. Variable declarations, assignments and simple calculations
• Example 2. Print patterns, such as, big letters using a specified character
• Example 3. Animating multiline text – one word at a time
• Example 4. Data structure problems
• Example 5. Text based Hangman game

The idea to include multiple examples as listed above is to demonstrate the power of sequence, condition and iteration all of which can be included in the main() method, to build good programming foundations with problem solving skills. By using the run command or the icon to run and execute their code in IntelliJ IDEA, new programmers reduce another step when getting started.

Changing an implicit class to a regular class

When you are ready to level up and work with other concepts like user defined classes, you could also covert the implicit classes and code that we used in the previous examples, to regular classes, as shown below:

What happens when you create a source code file with method main(), but no class declaration?

Behind the scenes, the Java compiler creates an implicit top level class, with a no-argument constructor, so that these classes don’t need to be treated in a way that is different to the regular classes.

Here’s a gif that shows a decompiled class for you for the source code file AnimateText.java:

Variations of the main method in the implicit class

As we are aware, a method can be overloaded. Does that imply an implicit class can define multiple main methods? If yes, which one of them qualifies as the ‘main’ method? This is an interesting question. First of all, know that you can’t define a static and non-static main method with the same signature, that is, with the same method parameters. The following method are considered valid main() methods in an implicit class:

If there is no valid main method detected, IntelliJ IDEA could add one for you, as shown in the following gif:

Educators could use this feature to introduce other concepts to the students in an incremental way

If you are an educator, you could introduce your students to other commonly used programming practices, such as creating methods- that is delegating part of your code to another method and calling it from the main method. You could also talk about passing values vs. variables to these methods.

The following gif shows how to do it:

Statements before super() – a preview language feature

Typically, we create alternative solutions for tasks that are necessary, but not officially permitted. For instance, executing statements before super() in a derived class constructor was not officially allowed, even though it was important for, say, validating values being passed to the base class constructor. A popular workaround involved creating static methods to validate values and then calling these methods on the arguments of super() . Though this approach worked well, it could make the code look complicated. This is changing with Statements before super() , a preview language feature in Java 22.

By using this feature, you can opt for a more direct approach, that is, drop the workaround of creating static methods, and execute code that validates arguments, just before calling super() . Terms and conditions still apply, such as, not accessing instance members of a derived class before execution of super() completes.

An example – Validating values passed to super() in a derived class constructor Imagine you need to create a class, say, IndustryElement , that extends class Element , which is defined as follows:

The constructor of the class Element misses checking if the atomicNumber is in the range of 1-118 (all known elements have atomic numbers between 1 to 118). Often the source code of a base class is not accessible or open for modification. How would you validate the values passed to atomicNumber in the constructor of class IndustryElement ?

Until Java 21, no statements were allowed to execute before super() . Here’s one of the ways we developers found a workaround by defining and calling static methods (static methods belong to a class and not to instances and can be executed before any instance of a class exists):

Starting Java 22, you could inline the contents of your static method in the constructor for your derived class, as shown in the following gif:

Here’s the resultant code for your reference:

Where else would you use this feature? If you are new to this feature, I’d recommend that you check out my detailed blog post, Constructor Makeover in Java 22 , in which I’ve covered this feature in detail using the following examples:

• Example 2 – base class constructor parameters that use annotations for validations
• Example 3 – Transforming variable values received in a derived class constructor, before calling a base class constructor.
• Example 4 – Executing statements before this() in constructor of Records
• Example 5 – Executing statements before this() in Enum constructors
• Example 6 – Executing statements before this() in classes

How does it work behind the scenes? The language syntax has been relaxed but it doesn’t change or impact the internal JVM instructions. There are no changes to the JVM instructions for this new feature because the order of execution of the constructors still remains unchanged – from base class to a derived class. Also, this feature still doesn’t allow you to use members of a derived class instance, until super() executes.

Let’s access and compare the instruction set of the constructor of class IndustryElement , before and after its modification – one that can execute statements before super() and the one that doesn’t. To do so, use the following command:

Here’s the instruction set for the constructor that doesn’t explicitly execute statements before super() and calls static methods to validate range of atomic number:

Here’s instruction set for the constructor that explicitly executes statements before super() to validate range of atomic number:

The most important point to note here is that in both the cases, the constructor of the base class, that is, Element is called, after the execution of all other statements. Essentially, it means, you are still doing the same thing, it is just packaged in a way that makes things easier for you.

I understand it is difficult to remember what each of these instruction codes means. Access the following link and search for the instruction code and following the above instructions set would be a breeze:

https://docs.oracle.com/javase/specs/jvms/se21/html/jvms-6.html#jvms-6.5.aload_n

Can you execute ‘any’ statements before calling super()?

No. If the statements before super() try to access instance variables or execute methods of your derived class, your code won’t compile. For example, if you change the static checkRange() method to an instance method, your code won’t compile, as shown below:

Unnamed Variables and Patterns

Starting Java 22, using Unnamed Variables & Patterns you can mark unused local variables, patterns and pattern variables to be ignored, by replacing their names (or their types and names) with an underscore, that is, _ . Since such variables and patterns no longer have a name, they are referred to as Unnamed variables and patterns. Ignoring unused variables would reduce the time and energy anyone would need to understand a code snippet. In the future, this could prevent errors :-). This language feature doesn’t apply to instance or class variables.

Are you wondering if replacing unused variables with _ is always a good idea, or do they imply code smells and should you consider refactoring your codebase to remove them? Those are good questions to ask. If you are new to this topic, I’d recommend you to check out my detailed blog post: Drop the Baggage: Use ‘_’ for Unnamed Local Variables and Patterns in Java 22 to find out answer to this question.

Since this is not a preview language feature, set Language Level in your Project Settings to ‘22 – Unnamed variables and patterns’ on both the Project and Modules tab, as shown in the below settings screenshot:

A quick example

The following gif gives a sneak peek into how an unused local variable, connection, is detected by IntelliJ IDEA, and could be replaced with an underscore, that is, _ .

The modified code shown in the preceding gif makes it clear that the local variable defined in the try-with-resources statement is unused, making it concise and easier to understand.

Unused Patterns and Pattern variables in switch constructs

Imagine you defined a sealed interface, say, GeometricShape , and records to represent shapes, such as, Point , Line , Triangle , Square , as shown in the following code:

Now assume you need a method that accepts an instance of GeometricShape and returns its area. Since Point and a Line are considered one-dimensional shapes, they wouldn’t have an area. Following is one of the ways to define such method that calculates and returns area:

In the previous example, the patterns int x , int y , Point a and Point B (for case label Line) remain unused as detected by IntelliJ IDEA. These could be replaced by an _ . Also, since all the record components of the case Point remain unused, it could be replaced as Point _ . This could also allow us to merge the first and second case labels. All of these steps are shown in the following gif:

Here’s the modified code for your reference:

In the preceding example, you can’t delete the pattern variables even if they are unused. The code must include the cases when the instance passed to the method calcArea() is of type Point and Line , so that it could return 0 for them.

Unused Patterns or variables with nested records

This feature also comes in quite handy for nested records with multiple unused patterns or pattern variables, as demonstrated using the following example code:

In the preceding code, since the if condition in the method checkFirstNameAndCountryCodeAgain uses only two pattern variables, others could be replaced using _ ; it reduced the noise in the code too.

Where else can you use this feature? Checkout my detailed detailed blog post: Drop the Baggage: Use ‘_’ for Unnamed Local Variables and Patterns in Java 22 to learn more about other use cases where this feature can be used:

• Requirements change, but you need side effects of constructs like an enhanced for-loop
• Unused parameters in exception handlers; whose signature can’t be modified
• Unused auto-closeable resources in try-with-resources statements

It isn’t advisable to use this feature without realising if an unused variable or pattern is a code smell or not. I used these examples to show that at times it might be better to refactor your code to get rid of the unused variable instead of just replacing it with an underscore, that is, _ .

• Unused lambda parameter
• Methods with multiple responsibilities

Preview Features

‘String Templates’, ‘Implicitly Declared Classes and Instance Main Methods’ and ‘Statements before super()’ are preview language features in Java 22. With Java’s new release cadence of six months, new language features are released as preview features. They may be reintroduced in later Java versions in the second or more preview, with or without changes. Once they are stable enough, they may be added to Java as a standard language feature.

Preview language features are complete but not permanent, which essentially means that these features are ready to be used by developers, although their finer details could change in future Java releases depending on developer feedback. Unlike an API, language features can’t be deprecated in the future. So, if you have feedback about any of the preview language features, feel free to share it on the JDK mailing list (free registration required).

Because of how these features work, IntelliJ IDEA is committed to only supporting preview features for the current JDK. Preview language features can change across Java versions, until they are dropped or added as a standard language feature. Code that uses a preview language feature from an older release of the Java SE Platform might not compile or run on a newer release.

In this blog post, I covered four Java 22 features – String Templates , Implicitly Declared Classes and Instance Main Methods , Statements before super() , and Unnamed variable and patterns .

String Templates is a great addition to Java. Apart from helping developers to work with strings that combine string constants and variables, they provide a layer of security. Custom String templates can be created with ease to accomplish multiple tasks, such as, to decipher letter combinations, either ignoring them or replacing them for added security.

Java language designers are reducing the ceremony that is required to write the first HelloWorld code for Java students, by introducing implicitly declared classes and instance main methods. New students can start with bare minimum main() method, such as, void main() and build strong programming foundation by polishing their skills with basics like sequence, selection and iteration.

In Java 22, the feature Statements before super() lets you execute code before calling super() in your derived class constructors, this() in your records or enums, so that you could validate the method parameters, or transform values, as required. This avoids creating workarounds like creating static methods and makes your code easier to read and understand. This feature doesn’t change how constructors would operate now vs. how they operated earlier – the JVM instructions remain the same.

Unnamed variables are local to a code construct, they don’t have a name, and they are represented by using an underscore, that is, _ . They can’t be passed to methods, or used in expressions. By replacing unused local variables in a code base with _ their intention is conveyed very clearly. It clearly communicates to anyone reading a code snippet that the variable is not used elsewhere. Until now, this intention could only be communicated via comments, which, unfortunately, all developers don’t write.

Happy Coding!

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Getting cozy with Java's new, softer side

New features like var, auto-compile, text blocks, record classes, and more are shifting java in subtle but powerful ways—toward a more flexible, dynamic future..

Contributor, InfoWorld |

Hidden compilation

Auto-compile multiple source files, a better build toolchain, simple web server, nested text blocks, record classes, structured concurrency.

Java has made some big shifts over the past few years, as seemingly disparate forces converged to make the platform easier to use. New features like auto-compile and the var keyword lower the bar for using Java, for beginners and veterans alike. Let's take a look at what's cooking in this new, friendlier Java.

Perhaps the most astounding thing about modern Java, at least for long-timers, is the presence of var support. One of Java’s defining characteristics is that it is strongly typed, but var loosens that a bit. Within a method, you can now define a reference using var where the compiler will keep track of the type for you.

After much hand-wringing about the wisdom of introducing this feature, Java developers everywhere have simply adopted it like it is the most obvious thing ever. Didn’t Java always let us do this?

No, it didn’t!

This new feature almost feels like running a source file without compiling it, but what's happening under the hood is a little more complicated. The .java file is still compiled, but JEP 330 makes it so it’s all hidden from you. So you can now do:

The runner compiles the source in memory and executes the first main class it discovers.

JEP 330 is limited to a single source file but hang on, because here comes JEP 458.

JEP 458 joins up with JEP 330 to let developers run multiple source files with hidden compilation. When a Java source refers to another, the Java launcher will compile the dependency in memory, load it, and provide it. In short, you can run entire programs of interrelated source files, so long as they exist on disk together, without an explicit compile step.

Is it me, or is Java evolving into something more dynamic? This is very cool.

The introduction to JEP 458 says it aims to:

Enhance the java application launcher to be able to run a program supplied as multiple files of Java source code. This will make the transition from small programs to larger ones more gradual, enabling developers to choose whether and when to go to the trouble of configuring a build tool.

This says in plain language that Java is working toward simplifying the lives of developers through better builds. The JEP even goes so far as to say that it is "not a goal to ease the use of external library dependencies in source-code programs," although " that may be the subject of a future JEP " (italics mine).

I understand here that Java's developers are working on making the tooling easier to use, even down to the dependency level— finally!  Maven is still my go-to build tool for complex projects, as it has been for 15 years, but the tool shows serious signs of age. (A new archetype project in Maven picks Java 1.7 as its default!) Compared to NPM, Maven is downright clunky; a real impediment to getting projects off the ground quickly—especially for beginners who have to learn the build tool while also learning Java.

A platform-ordained dependency manager could be just the thing. When I look at JEP 330 and JEP 458 together, I see not piecemeal band-aids to tooling usability, but the thoughtful rolling out of an integrated, in-platform toolchain. What is emerging is a Java toolchain designed to make it easy to start a project and incrementally adopt more sophisticated tooling as needed.

I know, JShell has been around for a long time now, but let’s acknowledge how nice it is to have a REPL-style runner for Java. Remember to use JShell to try out new ideas on the fly.

One day we woke up and Java had a command-line web server . You can learn all about Java's Simple Web Server here .

The key takeaway is: if you are using Java 18 or higher, your JDK install now includes a dead simple and easy way to serve files. As a result, the Java platform is a bit more one-stop, integrated, and complete. I have previously used Python or Node for basic file-serving needs; now, I can just do it all in Java.

Another feature Java developers have long envied in other platforms was an easy way to handle big chunks of text in code. JEP 378 brings the text blocks we've been looking for:

I don't know about you, but that block gives me a sigh of relief.

Text blocks can also nest quote characters freely:

The product of JEP 395, the record keyword, lets you create a POJO (plain old Java object) without manually adding getters, setters, toString , equals , and hashcode methods as you normally would. When you use record , the platform adds all those niceties for you:

The new record classes also allow for a great deal of customization, so you can have as much or as little added as you want.

New and improved switch

With JEP 361, Java’s switch syntax became more powerful and easier to use. This happened in two ways: a cleaner syntax and the ability to use  switch as an expression and not just a statement.

The switch now makes it possible to take clunky old syntax like this:

And turn it into something like this:

Equally awesome, you can use it as an expression to variable assignment (which is often all we are after, anyway):

Now, concurrency is never going to be a happy-go-lucky area of coding. There is something inherently mind-bending about working with multiple threads. Nevertheless, structured concurrency gives you possibly the easiest way to handle concurrency in the known coding universe:

When combined with Java’s new virtual threads , structured concurrency is a superpower among languages. Now, you can easily use concurrency in Java, without spawning operating system threads, and without leaving normal programming constructs.

Platform developers are working on multiple fronts to lower the bar for developers working in Java. They are improving the day-to-day lives of working coders and making it easier to get started with Java and experiment with it.

These efforts are especially impactful in that peculiar pocket of the developer world that I’m going to call “prototyping,” otherwise known as “playing around.” The more we can do to reduce the distance between thinking about trying something and actually trying it, the better. 

It’s great to see Java in such good shape. I like the direction it's moving toward and the people leading those efforts.

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Matthew Tyson is a founder of Dark Horse Group, Inc. He believes in people-first technology. When not playing guitar, Matt explores the backcountry and the philosophical hinterlands. He has written for JavaWorld and InfoWorld since 2007.

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