java assignment in while condition

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

Loops can execute a block of code as long as a specified condition is reached.

Loops are handy because they save time, reduce errors, and they make code more readable.

The while loop loops through a block of code as long as a specified condition is true :

In the example below, the code in the loop will run, over and over again, as long as a variable (i) is less than 5:

Try it Yourself »

Note: Do not forget to increase the variable used in the condition, otherwise the loop will never end!

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The Do/While Loop

The do/while loop is a variant of the while loop. This loop will execute the code block once, before checking if the condition is true, then it will repeat the loop as long as the condition is true.

The example below uses a do/while loop. The loop will always be executed at least once, even if the condition is false, because the code block is executed before the condition is tested:

Do not forget to increase the variable used in the condition, otherwise the loop will never end!

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Print i as long as i is less than 6.

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The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available. See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases. See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.

The while and do-while Statements

The while statement continually executes a block of statements while a particular condition is true . Its syntax can be expressed as:

The while statement evaluates expression , which must return a boolean value. If the expression evaluates to true , the while statement executes the statement (s) in the while block. The while statement continues testing the expression and executing its block until the expression evaluates to false . Using the while statement to print the values from 1 through 10 can be accomplished as in the following WhileDemo program:

You can implement an infinite loop using the while statement as follows:

The Java programming language also provides a do-while statement, which can be expressed as follows:

The difference between do-while and while is that do-while evaluates its expression at the bottom of the loop instead of the top. Therefore, the statements within the do block are always executed at least once, as shown in the following DoWhileDemo program:

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Assignment inside a Condition

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It’s very common in PHP to see code written like this:

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Frequently Asked Questions (FAQs) about Assignment Inside a Condition

What is an assignment inside a condition in programming.

An assignment inside a condition refers to the practice of assigning a value to a variable within a conditional statement such as an ‘if’ statement. This is a common practice in many programming languages including JavaScript, C++, and Python. It allows for more concise code as the assignment and the condition check can be done in a single line. However, it can also lead to confusion and potential bugs if not used carefully, as the assignment operation might be mistaken for a comparison operation.

Why is it considered bad practice to perform assignments in conditional expressions?

Assignments in conditional expressions can lead to confusion and potential bugs. This is because the assignment operator (=) can easily be mistaken for the equality operator (==). As a result, a condition that was meant to be a comparison could inadvertently become an assignment, leading to unexpected behavior in the code. Additionally, assignments in conditions can make the code more difficult to read and understand, particularly for less experienced programmers.

How can I avoid assignments in conditional expressions?

To avoid assignments in conditional expressions, you can separate the assignment and the condition check into two separate lines of code. For example, instead of writing if (x = getValue()) , you could write x = getValue(); if (x) . This makes the code clearer and reduces the risk of confusion or bugs.

Are there any situations where assignments in conditions are acceptable or even beneficial?

While generally discouraged, there are situations where assignments in conditions can be beneficial. For example, in a loop where a value needs to be updated and checked in each iteration, an assignment in the condition can make the code more concise. However, this should be done with caution and the code should be clearly commented to avoid confusion.

What is the difference between the assignment operator and the equality operator?

The assignment operator (=) is used to assign a value to a variable. For example, x = 5 assigns the value 5 to the variable x. On the other hand, the equality operator (==) is used to compare two values. For example, if (x == 5) checks whether the value of x is equal to 5.

How does TypeScript handle assignments in conditions?

TypeScript, like JavaScript, allows assignments in conditions. However, TypeScript has stricter type checking which can help catch potential errors caused by assignments in conditions. For example, if you try to assign a string to a variable that is supposed to be a number inside a condition, TypeScript will give a compile-time error.

What are some common bugs caused by assignments in conditions?

One common bug caused by assignments in conditions is an unintended assignment when a comparison was intended. For example, if (x = 5) will always be true because it assigns 5 to x, rather than checking if x is equal to 5. This can lead to unexpected behavior in the code.

How can I debug issues caused by assignments in conditions?

Debugging issues caused by assignments in conditions can be tricky because the code might not give any errors. One approach is to carefully check all conditional statements to ensure that they are using the correct operators. Using a linter or a static code analysis tool can also help catch these issues.

Can assignments in conditions be used in all programming languages?

Not all programming languages allow assignments in conditions. For example, Python does not allow assignments in conditions and will give a syntax error if you try to do so. Always check the syntax rules of the programming language you are using.

Are there any alternatives to assignments in conditions?

Yes, there are alternatives to assignments in conditions. One common alternative is to use a temporary variable to hold the value that needs to be assigned and checked. This can make the code clearer and easier to understand. Another alternative is to use a function that returns a value and then check that value in the condition.

James is a freelance web developer based in the UK, specialising in JavaScript application development and building accessible websites. With more than a decade's professional experience, he is a published author, a frequent blogger and speaker, and an outspoken advocate of standards-based development.

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While Loop Java: The Basics and Beyond

Are you finding it challenging to grasp the concept of while loops in Java? You’re not alone. Many developers find themselves puzzled when it comes to handling while loops in Java, but we’re here to help.

Think of a while loop in Java as a repeating if statement. It executes a block of code as long as a certain condition holds true. It’s like a persistent machine, tirelessly performing its task until told to stop.

In this guide, we’ll walk you through the syntax, usage, and common pitfalls of while loops in Java. We’ll cover everything from the basics of while loops to more advanced techniques, as well as alternative approaches.

Let’s get started and master the while loop in Java!

TL;DR: How Do I Use a While Loop in Java?

A while loop in Java is used to repeatedly execute a block of code as long as a certain condition is true. You can create a while loop in Java using the following syntax: while(condition) { // code to be executed } .

Here’s a simple example:

In this example, we initialize a variable i to 0. The while loop checks if i is less than 5. If the condition is true, it executes the code block inside the loop, which prints the value of i and then increments i by 1. This continues until i is no longer less than 5, at which point the loop stops executing.

This is a basic way to use a while loop in Java, but there’s much more to learn about controlling the flow of your programs with loops. Continue reading for more detailed information and advanced usage scenarios.

Table of Contents

Syntax and Basic Use of While Loop in Java

Advanced usage of while loop in java, comparing while loops with other loop structures in java, troubleshooting while loops in java, understanding the concept of loops in programming, expanding the use of while loops in java, wrapping up: java while loop.

The while loop in Java is a control flow statement that allows code to be executed repeatedly based on a given condition. The condition expression must be a boolean expression. The loop executes the block of code as long as the condition is true . Once the condition becomes false , the loop terminates. Let’s break down the syntax:

In this example, we have a variable count initialized to 0. The while loop checks if count is less than 5. If the condition is true, it executes the code within the loop, which prints the current value of count and then increments count by 1. The loop continues until count is no longer less than 5, at which point the loop stops executing.

Avoiding Infinite Loops

An important aspect to note while using while loops is the updating of the condition within the loop. If the condition never becomes false , the loop will continue indefinitely, creating what we call an infinite loop. This can cause your program to hang or crash. In the above example, we increment count within the loop, ensuring that the condition eventually becomes false (when count reaches 5), thus avoiding an infinite loop.

As you become more comfortable with while loops in Java, you’ll encounter situations that require more complex uses of these loops. Let’s look at two such scenarios: nested while loops and while-true loops.

Nested While Loops

A nested while loop is a while loop within another while loop. The inner loop completes all its iterations for each single iteration of the outer loop. Here’s an example:

In this example, for each iteration of the outer loop ( i loop), the inner loop ( j loop) runs completely, resulting in a total of 9 print statements.

While-True Loops

A while-true loop is a loop that continues indefinitely because its condition always remains true. It’s often used when the program needs to wait for a certain event to occur, or when it should run until the user decides to stop it. To stop a while-true loop, you can use the break statement. Here’s an example:

In this code, the message will print indefinitely until someCondition becomes true. When that happens, the break statement is executed, which immediately terminates the loop.

While loops are just one of the ways to control the flow of your program in Java. Other looping structures such as for loops and do-while loops offer alternative ways to handle repeated tasks. Let’s compare these structures and discuss when to use each one.

For loops are ideal when you know exactly how many times you want the loop to iterate. The syntax of a for loop includes initialization, condition, and increment/decrement in a single line, which can make your code more compact and readable. Here’s an example:

In this example, the loop will run exactly five times. The variable i is initialized to 0, incremented by 1 after each iteration, and the loop continues as long as i is less than 5.

Do-While Loops

Do-while loops are similar to while loops, but with a key difference: the do-while loop will execute the block of code at least once, even if the condition is false from the start. This is because the condition is checked after the first execution. Here’s an example:

In this example, even though i is not less than 5, the loop still executes once, printing the value of i , before checking the condition and terminating the loop.

In summary, while loops are a powerful tool for controlling the flow of your Java programs, but they’re not always the best tool for the job. Depending on the specifics of your task, a for loop or a do-while loop might be a better choice.

Like any aspect of programming, working with while loops in Java can present certain challenges. Let’s discuss some common issues you might encounter, such as infinite loops and off-by-one errors, and how to resolve them.

An infinite loop occurs when the condition in your while loop never becomes false. This causes the loop to run indefinitely, which can cause your program to become unresponsive. Here’s an example of an infinite loop:

To avoid infinite loops, make sure that the condition in your while loop will eventually become false. This usually involves modifying a variable within the loop so that it changes the result of the condition.

Off-By-One Errors

An off-by-one error occurs when a loop iterates one time too many or one time too few. This can happen if you’re not careful with the condition in your while loop. For example:

In this example, the loop runs six times, not five, because it also executes when i is equal to 5. To avoid off-by-one errors, be sure to double-check your conditions and consider the initial and final values of your loop variable.

Best Practices

To ensure your while loops work as intended, follow these best practices:

• Always initialize your loop variables.
• Make sure the loop condition changes within the loop.
• Be mindful of off-by-one errors.
• Test your loops with different inputs to ensure they work correctly in all scenarios.

With these tips in mind, you’ll be well-equipped to tackle while loops in Java effectively and efficiently.

Loops are fundamental constructs in any programming language, including Java. They allow us to execute a block of code multiple times, which is often necessary in programming tasks. Whether it’s processing items in a collection, repeating an operation until a condition is met, or simply waiting for an event to occur, loops are an indispensable part of a programmer’s toolkit.

Why Are Loops Important?

Imagine you need to print the numbers from 1 to 100. Without a loop, you’d have to write a print statement 100 times! With a loop, you can accomplish this task with just a few lines of code:

This not only makes your code more concise and readable, but it also makes it more flexible and maintainable. If you later decide to print the numbers up to 200, you only need to change a single number in your code.

How Do Loops Work in Java?

In Java, a loop typically consists of three parts: initialization, condition, and update. Let’s look at these parts in the context of a while loop:

• Initialization : Before the loop starts, we initialize a variable ( i in this case) that we’ll use in the loop condition.
• Condition : This is a boolean expression that determines whether the loop should continue. If the condition is true, the loop executes. If it’s false, the loop terminates.
• Update : Inside the loop, we update the loop variable in some way. This is crucial for ensuring that the loop condition eventually becomes false, preventing infinite loops.

In the next sections, we’ll delve deeper into the specifics of while loops in Java, including their syntax, usage, and common pitfalls.

While loops in Java are not just limited to simple tasks. They can be a powerful tool when dealing with larger projects or scripts, allowing you to control the flow of your program in a dynamic way. Whether it’s processing large amounts of data, controlling user interactions, or managing the behavior of threads, while loops often play a crucial role.

For example, in a large project, you might use a while loop to continuously check for user input, to monitor the status of a database, or to keep a thread running until a certain condition is met.

In this example, the loop continues running as long as the userHasQuit variable is false . Inside the loop, the program might check for user input, process data, and update a database. When the user decides to quit (setting userHasQuit to true ), the loop stops, and the program can perform any necessary cleanup operations.

Exploring Related Topics: Recursion and Multi-Threading

As you get more comfortable with while loops, you might want to explore related topics such as recursion and multi-threading in Java. Recursion is a concept where a method calls itself to solve a problem, and it can often be used as an alternative to traditional looping structures. Multi-threading allows a program to perform multiple tasks concurrently, and controlling the flow of these threads often involves careful use of while loops and other control structures.

Further Resources for Mastering Java Loops

To continue your journey in mastering loops in Java, here are some additional resources that you might find helpful:

• Fundamentals Covered: Loops in Java – Understand loop scoping and variable visibility in Java.

Recursion in Java – Understand recursion in Java for solving problems through self-referential function calls.

Using For-Each Loop in Java – Master the for-each loop for concise and readable code in Java.

Oracle Java Tutorials: Control Flow Statements – Understand the procuring flow of statements in Java by Oracle.

GeeksforGeeks’ Loops in Java – Comprehensive guide on utilizing loops in Java programming.

W3Schools’ Java While Loop Tutorial – Learn the essentials of Java while loop with W3Schools tutorials.

These resources offer in-depth discussions, examples, and exercises on while loops and other control flow statements in Java, helping you further solidify your understanding and improve your coding skills.

In this comprehensive guide, we’ve delved into the world of while loops in Java, starting from the basics and moving towards more advanced concepts.

We began with the fundamentals, understanding the importance of loops in programming and how they work in Java. We then explored the syntax and basic usage of while loops, including how to avoid common pitfalls like infinite loops and off-by-one errors. We also ventured into more advanced territory, discussing nested while loops and while-true loops, and how they can be used effectively in Java programming.

In addition to while loops, we also compared them with other looping structures in Java, such as for loops and do-while loops, providing you with a broader perspective on how to control the flow of your programs. Here’s a quick comparison of these loops:

Whether you’re just starting out with Java or you’re looking to level up your looping skills, we hope this guide has given you a deeper understanding of while loops and their usage in Java.

Mastering while loops is a crucial step in becoming proficient in Java. With this knowledge, you’re now well-equipped to tackle complex programming tasks with more efficiency and confidence. Happy coding!

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Gabriel is the owner and founder of IOFLOOD.com , an unmanaged dedicated server hosting company operating since 2010.Gabriel loves all things servers, bandwidth, and computer programming and enjoys sharing his experience on these topics with readers of the IOFLOOD blog.

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1.7 Java | Assignment Statements & Expressions

An assignment statement designates a value for a variable. An assignment statement can be used as an expression in Java.

After a variable is declared, you can assign a value to it by using an assignment statement . In Java, the equal sign = is used as the assignment operator . The syntax for assignment statements is as follows:

An expression represents a computation involving values, variables, and operators that, when taking them together, evaluates to a value. For example, consider the following code:

You can use a variable in an expression. A variable can also be used on both sides of the =  operator. For example:

In the above assignment statement, the result of x + 1  is assigned to the variable x . Let’s say that x is 1 before the statement is executed, and so becomes 2 after the statement execution.

To assign a value to a variable, you must place the variable name to the left of the assignment operator. Thus the following statement is wrong:

Note that the math equation  x = 2 * x + 1  ≠ the Java expression x = 2 * x + 1

Which is equivalent to:

And this statement

is equivalent to:

Note: The data type of a variable on the left must be compatible with the data type of a value on the right. For example, int x = 1.0 would be illegal, because the data type of x is int (integer) and does not accept the double value 1.0 without Type Casting .

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Chapter 7. Conditional execution

Recall our MovingBall program of Figure 6.3 , in which a red ball moved steadily down and to the right, eventually moving off the screen. Suppose that instead we want the ball to bounce when it reaches the window's edge. To do this, we need some way to test whether it has reached the edge. The most natural way of accomplishing this in Java is to use the if statement that we study in this chapter.

7.1. The if statement

An if statement tells the computer to execute a sequence of statements only if a particular condition holds. It is sometimes called a conditional statement , since it allows us to indicate that the computer should execute some statements only in some conditions.

if ( <thisIsTrue> ) {      <statementsToDoIfTrue> }

When the computer reaches the if statement, it evaluates the condition in parentheses. If the condition turns out to be true , then the computer executes the if statement's body and then continues to any statements following. If the condition turns out to be false , it skips over the body and goes directly to whatever follows the closing brace. This corresponds to the flowchart in Figure 7.1 .

Figure 7.1: A flowchart for the if statement.

An if statement looks a lot like a while loop: The only visual difference is that it uses the if keyword in place of while . And it acts like a while loop also, except that after completing the if statement's body, the computer does not consider whether to execute the body again.

The following fragment includes a simple example of an if statement in action.

double   num  =  readDouble (); if ( num  < 0.0) {      num  = - num ; }

In this fragment, we have a variable num referring to a number typed by the user. If num is less than 0, then we change num to refer to the value of - num instead, so that num will now be the absolute value of what the user typed. But if num is not negative, the computer will skip the num  = - num statement; num will still be the absolute value of what the user typed.

7.2. The bouncing ball

We can now turn to our MovingBall program, modifying it so that the ball will bounce off the edges of the window. To accomplish this, before each movement, we will test whether the ball has crossed an edge of the window: The movement in the x direction should invert if the ball has crossed the east or west side, and the movement in the y direction should invert if the ball has crossed the north or south side. The program of Figure 7.2 accomplishes this.

Figure 7.2: The BouncingBall program.   1    import   acm . program .*;   2    import   acm . graphics .*;   3    import   java . awt .*;   4      5    public   class   BouncingBall   extends   GraphicsProgram  {   6        public   void   run () {   7            GOval   ball  =  new   GOval (25, 25, 50, 50);   8            ball . setFilled ( true );   9            ball . setFillColor ( new   Color (255, 0, 0));  10            add ( ball );  11     12            double   dx  = 3;  13            double   dy  = -4;  14            while ( true ) {  15                pause (40);  16                if ( ball . getX () +  ball . getWidth () >=  getWidth ()  17                       ||  ball . getX () <= 0.0) {  18                    dx  = - dx ;  19               }  20                if ( ball . getY () +  ball . getHeight () >=  getHeight ()  21                       ||  ball . getY () <= 0.0) {  22                    dy  = - dy ;  23               }  24                ball . move ( dx ,  dy );  25           }  26       }  27   }

If you think about it carefully, the simulation of this program isn't perfect: There will be frames where the ball has crossed over the edge, so that only part of the circle is visible. This isn't a big problem, for a combination of reasons: First, the ball will be over the border only for a single frame (i.e., for only a fleeting few milliseconds), and second, the effect is barely visible because it affects only a few pixels of the ball's total size. Anyway, our eye expects to see a rubber ball flatten against the surface briefly before bouncing back in the opposite direction. If we were to repair this problem, then we would perceive the ball to be behaving more like a billiard ball. In any case, we won't attempt to repair the problem here.

7.3. The else clause

Sometimes we want a program to do one thing if the condition is true and another thing if the condition is false. In this case the else keyword comes in handy.

if ( <thisIsTrue> ) {      <statementsToDoIfTrue> }  else  {      <statementsToDoIfFalse> }

Figure 7.3 contains a flowchart diagramming this type of statement.

Figure 7.3: A flowchart for the else clause.

For example, if we wanted to compute the larger of two values typed by the user, then we might use the following code fragment.

double   first  =  readDouble (); double   second  =  readDouble (); double   max ; if ( first  >  second ) {      max  =  first ; }  else  {      max  =  second ; } print ( max );

This fragment will first read the two numbers first and second from the user. It then creates a variable max that will end up holding the larger of the two. This function says assign the value of first to max if first holds a larger value than second ; otherwise — it says — assign max the value of second .

Sometimes it's useful to string several possibilities together. This is possible by inserting else   if clauses into the code.

double   score  =  readDouble (); double   gpa ; if ( score  >= 90.0) {      gpa  = 4.0; }  else   if ( score  >= 80.0) {      gpa  = 3.0; }  else   if ( score  >= 70.0) {      gpa  = 2.0; }  else   if ( score  >= 60.0) {      gpa  = 1.0; }  else  {      gpa  = 0.0; }

You can string together as many else   if clauses as you want. Having an else clause at the end is not required.

Note that, if the user types 95 as the computer executes the above fragment, the computer would set gpa to refer to 4.0. It would not also set gpa to refer to 3.0, even though it's true that score  >= 80.0 . This is because the computer checks an else   if clause only if the preceding conditions all turn out to be false .

As an example using graphics, suppose we want our hot-air balloon animation to include a moment when the hot-air balloon is firing its burner, so it briefly goes up before it resumes its descent. To do this, we'll modify the loop in Figure 6.4 to track which frame is currently being drawn, and we'll use an if statement with else clauses to select in which direction the balloon should move for the current frame.

int   frame  = 0;  // tracks which frame we are on while ( balloon . getY () + 70 <  getHeight ()) {      pause (40);      if ( frame  < 100) {         // the balloon is in free-fall          balloon . move (1, 2);     }  else   if ( frame  < 200) {  // it fires its burner          balloon . move (1, -1);     }  else  {                  // it no longer fires its burner          balloon . move (1, 1);     }      frame ++; }

7.4. Braces

When the body of a while or if statement holds only a single statement, the braces are optional. Thus, we could write our max code fragment from earlier as follows, since both the if and the else clauses contain a single statement. (We could also include braces on just one of the two bodies.)

double   max ; if ( first  >  second )      max  =  first ; else      max  =  second ;

I recommend that you include the braces anyway. This saves you trouble later, should you decide to add additional statements into the body of the statement. And it makes it easier to keep track of braces, since each indentation level requires a closing right brace.

In fact, Java technically doesn't have an else   if clause. In our earlier gpa examples, Java would actually interpret the if statements as follows.

if ( score  >= 90.0) {      gpa  = 4.0; }  else      if ( score  >= 80.0) {          gpa  = 3.0;     }  else          if ( score  >= 70.0) {              gpa  = 2.0;         }  else              if ( score  >= 60.0) {                  gpa  = 1.0;             }  else  {                  gpa  = 0.0;             }

Each else clause includes exactly one statement — which happens to be an if statement with an accompanying else clause in each case. Thus, when we were talking about else   if clauses, we were really just talking about a more convenient way of inserting white space for the special case where an else clause contains a single if statement.

7.5. Variables and compile errors

7.5.1. variable scope.

Java allows you to declare variables within the body of a while or if statement, but it's important to remember the following: A variable is available only from its declaration down to the end of the braces in which it is declared. This region of the program text where the variable is valid is called its scope .

Check out this illegal code fragment.

 29    if ( first  >  second ) {  30        double   max  =  first ;  31   }  else  {  32        double   max  =  second ;  33   }  34    print ( max );  // Illegal!

On trying to compile this, the compiler will point to line 34 and display a message saying something like, Cannot find symbol max . What's going on here is that the declaration of max inside the if 's body persists only until the brace closing that if statement's body; and the declaration of max in the else 's body persists only until the brace closing that body. Thus, at the end, outside either of these bodies, max does not exist as a variable.

A novice programmer might try to patch over this error by declaring max before the if statement.

double   max  = 0.0; if ( first  >  second ) {      double   max  =  first ;  // Illegal! }  else  {      double   max  =  second ;  // Illegal! } print ( max );

The Java compiler should respond by flagging the second and third declarations of max with a message like max is already defined. In Java, each time you label a variable with a type, it counts as a declaration; and you can only declare each variable name once. Thus, the compiler will understand the above as an attempt to declare two different variables with the same name. It will insist that each variable once and only once.

7.5.2. Variable initialization

Another common mistake of beginners is to use an else   if clause where an else clause is completely appropriate.

 46    double   max ;  47    if ( first  >  second ) {  48        max  =  first ;  49   }  else   if ( second  >=  first ) {  50        max  =  second ;  51   }  52    print ( max );

Surprisingly, the compiler will complain about line 52, with a message like variable max might not have been initialized. (Recall that initialization refers to the first assignment of a value to a variable.) The compiler is noticing that the print invocation uses the value of max , since it will send the variable's value as a parameter. But, it reasons, perhaps max may not yet have been assigned a value when it reaches that point.

In this particular fragment, the computer is reasoning that while the if and else   if bodies both initialize max , it may be possible for both conditions to be false ; and in that case, max will not be initialized. This may initially strike you as perplexing: Obviously, it can't be that both the if and the else   if condition turn out false . But our reasoning hinges on a mathematical fact that the compiler is not itself sophisticated enough to recognize.

You might hope for the compiler to be able to recognize such situations. But it is impossible for the compiler to reliably identify such situations. This results from what mathematicians and computer scientists call the halting problem . The halting problem asks for a program that reads another program and reliably predicts whether that other program will eventually reach its end. Such a program is provably impossible to write.

This result implies that there's no way to solve the initialization problem perfectly, because if we did have such a program, we could modify it to solve the halting problem. Our modification for solving the halting problem is fairly simple: Our modified program would first read the program for which we want to answer the halting question. Then we place a variable declaration at the program's beginning, and then at any point where the program would end we place a variable assignment. And finally we hand the resulting program into the supposed program for determining variable initialization. Out would pop the answer to the halting question for the program under inquiry.

That said, there's nothing preventing the compiler writers from trying at least to identify the easy cases. And you might hope that they'd be thorough enough to identify that given two numbers, the first is either less than, equal to, or greater than the second. But this would inevitably lead to a complex set of rules when the compiler identifies initialization and when not, and the Java designers felt it best to keep the rules simple enough for regular programmers to remember.

The solution in this case is to recognize that, in fact, we don't need the else   if condition: Whenever the if condition turns out to be false , we the else   if body to occur. Thus, doing that extra test both adds extra verbiage and slows down the program slightly. If use an else clause instead of an else   if , the compiler will reason successfully that max will be initialized, and it won't complain.

(Novice programmers are sometimes tempted to simply initialize max on line 46 to avoid the message. This removes the compiler message, and the program will work. But patching over compiler errors like this is a bad habit. You're better off addressing the problem at its root.)

By the way, Java compilers are some of strictest I've seen about uninitialized variables. It can occassionally be a bit irritating to have to repair a program with an alleged uninitialized variable, when we are certain that the program would run flawlessly as written. The reason the compiler is so aggressive is that it's aggressively trying to help you debug your programs. Suppose, for the sake of argument, that it was a real problem in the program. If the compiler didn't complain, you'd be relying on the test cases to catch the problem. If the test cases didn't catch it, you'd be misled into releasing a erroneous program. Even if they did catch it, you're stuck trying to figure out the cause, which can take quite a while. A problem like an uninitialized variable can be very difficult to track down by trial and error; but with the compiler pointing to it for you, it becomes much easier.

Describe all the errors in the following code fragment, and write a version correcting all of them.

int   k  =  readInt (); int   ch ; if   k  = 2 {      ch  = 1.0; } ch  *= 2;

Modify the BouncingBall program to provide the illusion of gravity. To do this, the y component of the ball's velocity should increase by a fixed amount (maybe 0.2 per frame), which accounts for the acceleration due to gravity. Also, when the ball bounces off an edge of the window, the velocity should become 90% of what it was previously; this way, each bounce will be successively smaller.

There are several subtleties involved with doing this well. Realistic bounces are relatively easy at the beginning, when the bounces are big; but as the bounces become much smaller, some peculiar behavior will likely appear: For example, the ball may appear to reach a point where bounces no longer become smaller, or it may appear to be stuck below the bottom border of the window.

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Overview of Java

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Operators in Java

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Input/output in java.

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Flow Control in Java

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Java Assignment Operators with Examples

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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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Idiom #252 Conditional assignment

Assign to the variable x the string value "a" if calling the function condition returns true , or the value "b" otherwise.

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Java Tutorial

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Conditional AND

The operator is applied between two Boolean expressions. It is denoted by the two AND operators (&&). It returns true if and only if both expressions are true, else returns false.

Conditional OR

The operator is applied between two Boolean expressions. It is denoted by the two OR operator (||). It returns true if any of the expression is true, else returns false.

Let's create a Java program and use the conditional operator.

ConditionalOperatorExample.java

Ternary Operator

The meaning of ternary is composed of three parts. The ternary operator (? :) consists of three operands. It is used to evaluate Boolean expressions. The operator decides which value will be assigned to the variable. It is the only conditional operator that accepts three operands. It can be used instead of the if-else statement. It makes the code much more easy, readable, and shorter.

Note: Every code using an if-else statement cannot be replaced with a ternary operator.

The above statement states that if the condition returns true, expression1 gets executed, else the expression2 gets executed and the final result stored in a variable.

Let's understand the ternary operator through the flowchart.

TernaryOperatorExample.java

Let's see another example that evaluates the largest of three numbers using the ternary operator.

LargestNumberExample.java

In the above program, we have taken three variables x, y, and z having the values 69, 89, and 79, respectively. The expression (x > y) ? (x > z ? x : z) : (y > z ? y : z) evaluates the largest number among three numbers and store the final result in the variable largestNumber. Let's understand the execution order of the expression.

First, it checks the expression (x > y) . If it returns true the expression (x > z ? x : z) gets executed, else the expression (y > z ? y : z) gets executed.

When the expression (x > z ? x : z) gets executed, it further checks the condition x > z . If the condition returns true the value of x is returned, else the value of z is returned.

When the expression (y > z ? y : z) gets executed it further checks the condition y > z . If the condition returns true the value of y is returned, else the value of z is returned.

Therefore, we get the largest of three numbers using the ternary operator.

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