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Java if...else Statement

In programming, we use the if..else statement to run a block of code among more than one alternatives.

For example, assigning grades (A, B, C) based on the percentage obtained by a student.

• if the percentage is above 90 , assign grade A
• if the percentage is above 75 , assign grade B
• if the percentage is above 65 , assign grade C

1. Java if (if-then) Statement

The syntax of an if-then statement is:

Here, condition is a boolean expression such as age >= 18 .

• if condition evaluates to true , statements are executed
• if condition evaluates to false , statements are skipped

Working of if Statement

Example 1: Java if Statement

In the program, number < 0 is false . Hence, the code inside the body of the if statement is skipped .

Note: If you want to learn more about about test conditions, visit Java Relational Operators and Java Logical Operators .

We can also use Java Strings as the test condition.

Example 2: Java if with String

In the above example, we are comparing two strings in the if block.

2. Java if...else (if-then-else) Statement

The if statement executes a certain section of code if the test expression is evaluated to true . However, if the test expression is evaluated to false , it does nothing.

In this case, we can use an optional else block. Statements inside the body of else block are executed if the test expression is evaluated to false . This is known as the if-...else statement in Java.

The syntax of the if...else statement is:

Here, the program will do one task (codes inside if block) if the condition is true and another task (codes inside else block) if the condition is false .

How the if...else statement works?

Example 3: Java if...else Statement

In the above example, we have a variable named number . Here, the test expression number > 0 checks if number is greater than 0.

Since the value of the number is 10 , the test expression evaluates to true . Hence code inside the body of if is executed.

Now, change the value of the number to a negative integer. Let's say -5 .

If we run the program with the new value of number , the output will be:

Here, the value of number is -5 . So the test expression evaluates to false . Hence code inside the body of else is executed.

3. Java if...else...if Statement

In Java, we have an if...else...if ladder, that can be used to execute one block of code among multiple other blocks.

Here, if statements are executed from the top towards the bottom. When the test condition is true , codes inside the body of that if block is executed. And, program control jumps outside the if...else...if ladder.

If all test expressions are false , codes inside the body of else are executed.

How the if...else...if ladder works?

Example 4: Java if...else...if Statement

In the above example, we are checking whether number is positive, negative, or zero . Here, we have two condition expressions:

• number > 0 - checks if number is greater than 0
• number < 0 - checks if number is less than 0

Here, the value of number is 0 . So both the conditions evaluate to false . Hence the statement inside the body of else is executed.

Note : Java provides a special operator called ternary operator , which is a kind of shorthand notation of if...else...if statement. To learn about the ternary operator, visit Java Ternary Operator .

4. Java Nested if..else Statement

In Java, it is also possible to use if..else statements inside an if...else statement. It's called the nested if...else statement.

Here's a program to find the largest of 3 numbers using the nested if...else statement.

Example 5: Nested if...else Statement

In the above programs, we have assigned the value of variables ourselves to make this easier.

However, in real-world applications, these values may come from user input data, log files, form submission, etc.

Table of Contents

• Introduction
• Java if (if-then) Statement
• Example: Java if Statement
• Java if...else (if-then-else) Statement
• Example: Java if else Statement
• Java if..else..if Statement
• Example: Java if..else..if Statement
• Java Nested if..else Statement

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Equality, Relational, and Conditional Operators

The equality and relational operators.

The equality and relational operators determine if one operand is greater than, less than, equal to, or not equal to another operand. The majority of these operators will probably look familiar to you as well. Keep in mind that you must use " == ", not " = ", when testing if two primitive values are equal.

The following program, ComparisonDemo , tests the comparison operators:

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The && and || operators perform Conditional-AND and Conditional-OR operations on two boolean expressions. These operators exhibit "short-circuiting" behavior, which means that the second operand is evaluated only if needed.

The following program, ConditionalDemo1 , tests these operators:

Another conditional operator is ?: , which can be thought of as shorthand for an if-then-else statement (discussed in the Control Flow Statements section of this lesson). This operator is also known as the ternary operator because it uses three operands. In the following example, this operator should be read as: "If someCondition is true , assign the value of value1 to result . Otherwise, assign the value of value2 to result ."

The following program, ConditionalDemo2 , tests the ?: operator:

Because someCondition is true, this program prints "1" to the screen. Use the ?: operator instead of an if-then-else statement if it makes your code more readable; for example, when the expressions are compact and without side-effects (such as assignments).

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The instanceof operator compares an object to a specified type. You can use it to test if an object is an instance of a class, an instance of a subclass, or an instance of a class that implements a particular interface.

The following program, InstanceofDemo , defines a parent class (named Parent ), a simple interface (named MyInterface ), and a child class (named Child ) that inherits from the parent and implements the interface.

When using the instanceof operator, keep in mind that null is not an instance of anything.

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You already know that Java supports the usual logical conditions from mathematics:

• Less than: a < b
• Less than or equal to: a <= b
• Greater than: a > b
• Greater than or equal to: a >= b
• Equal to a == b
• Not Equal to: a != b

You can use these conditions to perform different actions for different decisions.

Java has the following conditional statements:

• Use if to specify a block of code to be executed, if a specified condition is true
• Use else to specify a block of code to be executed, if the same condition is false
• Use else if to specify a new condition to test, if the first condition is false
• Use switch to specify many alternative blocks of code to be executed

The if Statement

Use the if statement to specify a block of Java code to be executed if a condition is true .

Note that if is in lowercase letters. Uppercase letters (If or IF) will generate an error.

In the example below, we test two values to find out if 20 is greater than 18. If the condition is true , print some text:

Try it Yourself »

We can also test variables:

Example explained

In the example above we use two variables, x and y , to test whether x is greater than y (using the > operator). As x is 20, and y is 18, and we know that 20 is greater than 18, we print to the screen that "x is greater than y".

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The else Statement

Use the else statement to specify a block of code to be executed if the condition is false .

In the example above, time (20) is greater than 18, so the condition is false . Because of this, we move on to the else condition and print to the screen "Good evening". If the time was less than 18, the program would print "Good day".

The else if Statement

Use the else if statement to specify a new condition if the first condition is false .

In the example above, time (22) is greater than 10, so the first condition is false . The next condition, in the else if statement, is also false , so we move on to the else condition since condition1 and condition2 is both false - and print to the screen "Good evening".

However, if the time was 14, our program would print "Good day."

Test Yourself With Exercises

Print "Hello World" if x is greater than y .

Start the Exercise

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If-Else Java: Mastering Decision Making in Code

Ever found yourself puzzled on how to make your Java program make decisions? You’re not alone. Many developers find themselves at crossroads when it comes to controlling the flow of their Java programs. Think of the ‘if-else’ statement in Java as a traffic light – it regulates the flow of your program, directing it where to go based on certain conditions.

This guide will take you through the journey of mastering the ‘if-else’ statement in Java , from the basics to more advanced usage. We’ll cover everything from writing your first if-else statement, understanding its flow, to handling more complex scenarios with nested if-else and if-else-if ladder. We’ll also explore alternative approaches to control the flow of a Java program.

So, let’s dive in and start mastering the if-else statement in Java!

TL;DR: How Do I Use the If-Else Statement in Java?

An ‘if-else’ statement is used to perform different actions based on different conditions, defined with the syntax: if (condition) {// code if condition is true} else {code if condition is false} It’s like a fork in the road, directing your program based on the conditions you set.

Here’s a simple example:

In this example, the ‘if-else’ statement checks a condition. If the condition is true, it executes the code within the ‘if’ block. If the condition is false, it executes the code within the ‘else’ block. It’s a simple yet powerful way to control the flow of your program.

But there’s so much more to the ‘if-else’ statement in Java. Continue reading for a deeper understanding, more advanced usage scenarios, and alternative approaches.

Table of Contents

Beginner’s Guide to If-Else in Java

Intermediate-level if-else in java, exploring alternatives to if-else in java, troubleshooting java if-else statements, control flow: the heart of programming, if-else in larger java projects, wrapping up: mastering if-else statements in java.

The ‘if-else’ statement in Java is a cornerstone of decision-making in your program. It allows you to execute different blocks of code based on specific conditions. Let’s break down how to use it step by step.

Writing Your First If-Else Statement

Here’s a simple example of how to use the ‘if-else’ statement:

In this example, we’re checking if the score is greater than or equal to 90. If it is, the program will print ‘Excellent!’, otherwise it will print ‘Good job, but there’s room for improvement.’

Advantages of Using If-Else

The ‘if-else’ statement is a powerful tool for controlling your program’s flow. It allows you to specify different actions for different conditions, making your program more flexible and adaptable.

Pitfalls to Watch Out For

While the ‘if-else’ statement is incredibly useful, it’s important to use it correctly. Be careful not to write conditions that are always true or always false, as this can lead to unexpected behavior. Additionally, remember that the order of your conditions matters. The program will check the conditions in the order they appear, so make sure you’re considering all possible scenarios.

As you gain more experience with Java, you’ll find situations where a simple ‘if-else’ statement isn’t enough. This is where more complex structures like nested ‘if-else’ and ‘if-else-if’ ladders come in.

Nested If-Else Statements

A nested ‘if-else’ statement is an ‘if-else’ statement within another ‘if-else’ statement. It allows for more complex decision-making in your program.

Here’s an example:

In this example, if the score is not greater than or equal to 90, the program checks another condition: if the score is greater than or equal to 80. If it is, it prints ‘Very Good!’. If not, it prints ‘Good job, but there’s room for improvement.’

If-Else-If Ladder

An ‘if-else-if’ ladder is a series of conditions checked one after the other. It’s useful when you have multiple conditions to check.

In this example, the program checks the conditions in order. If the score is not greater than or equal to 90, it checks if the score is greater than or equal to 80. If it is, it prints ‘Very Good!’. If not, it prints ‘Good job, but there’s room for improvement.’

While ‘if-else’ statements are a fundamental part of controlling flow in Java, they aren’t the only tool at your disposal. Another powerful tool is the ‘switch’ statement.

The Power of Switch Statements

The ‘switch’ statement in Java allows you to select one of many code blocks to be executed. It’s a more readable and efficient alternative to the ‘if-else-if’ ladder when dealing with multiple conditions.

In this example, the ‘switch’ statement checks the value of ‘day’. Depending on the value, it assigns a different string to ‘dayOfWeek’. If ‘day’ is not a value between 1 and 7, it assigns ‘Invalid day’ to ‘dayOfWeek’.

Advantages and Drawbacks of Switch Statements

Switch statements can make your code cleaner and easier to read when dealing with multiple conditions. However, they are less flexible than ‘if-else’ statements. They can only be used with discrete values and cannot handle ranges or complex conditions.

Making the Right Choice

When deciding whether to use ‘if-else’ or ‘switch’, consider the complexity of your conditions. If you’re dealing with ranges or complex conditions, ‘if-else’ is the way to go. If you’re dealing with multiple discrete values, consider using ‘switch’ for cleaner, more readable code.

Like any tool, ‘if-else’ statements in Java can present challenges, especially when used in complex ways. Let’s look at some common issues and their solutions.

Dealing with Syntax Errors

One of the most common issues when using ‘if-else’ statements is syntax errors. These can occur if you forget a bracket, misspell a keyword, or make other typographical errors. For example:

In this case, the opening bracket after the ‘if’ statement is missing, causing a syntax error. The solution is to correct the syntax:

Handling Logical Errors

Another common issue is logical errors, where the code runs without errors, but doesn’t produce the expected result. This usually happens due to incorrect conditions in the ‘if-else’ statement.

For example, consider this code:

Even though the score is 85, the program prints ‘Excellent!’ because the condition checks if the score is less than or equal to 90, not greater than or equal to. The solution is to correct the condition:

These are just a few examples of the challenges you might face when using ‘if-else’ statements in Java. Remember, the key to effective troubleshooting is understanding the problem, reading error messages carefully, and knowing how ‘if-else’ statements work.

Control flow is a fundamental concept in programming. It’s the order in which your program executes instructions. In Java, control flow is managed using conditional statements like ‘if-else’, loops, and other constructs.

The Role of If-Else in Control Flow

The ‘if-else’ statement is a conditional statement that plays a pivotal role in control flow. It allows your program to choose a path of execution based on whether a condition is true or false.

Here’s a simple ‘if-else’ statement:

In this example, the program checks the condition. If it’s true, it executes the code within the ‘if’ block. If it’s false, it executes the code within the ‘else’ block.

Understanding Conditional Statements

Conditional statements are the building blocks of control flow. They allow your program to make decisions, repeat actions, and handle complex logic. The ‘if-else’ statement is one of the most common conditional statements, but there are others, like ‘switch’ and ‘for’, each with its unique use cases.

By mastering ‘if-else’ and other conditional statements, you’ll be able to write Java programs that can handle complex tasks, making you a more effective and versatile developer.

The ‘if-else’ statement isn’t just for simple programs or exercises. It’s a fundamental tool that you’ll use in almost every Java project, no matter how large or complex.

Integrating If-Else with Loops

In larger projects, you’ll often find ‘if-else’ statements used in conjunction with loops. For example, you might use a ‘for’ or ‘while’ loop to iterate over a collection of items, and an ‘if-else’ statement to perform different actions based on each item.

In this example, the program uses a ‘for’ loop to iterate over the numbers 0 through 9. For each number, it uses an ‘if-else’ statement to check if the number is even or odd, and prints a message accordingly.

If-Else and Exception Handling

‘If-else’ statements are also often used in exception handling, a crucial part of any Java program. You might use an ‘if-else’ statement to check if a certain condition is met before performing an action that could throw an exception.

In this example, the program uses an ‘if-else’ statement to check if ‘str’ is not null before trying to get its length. If ‘str’ is null, it prints a warning message instead of throwing a NullPointerException.

Further Resources for Mastering If-Else in Java

If you want to dive deeper into the ‘if-else’ statement in Java and related topics, here are some resources to check out:

• IOFlood’s Complete Guide to Java Loops explores nested loops for complex iteration patterns in Java.

Java Switch Statement – Explore the switch statement in Java for multi-branch decision-making.

Using Else-If in Java – Master the else-if construct for complex decision-making in Java programs.

Java if-else statement by Oracle : Oracle’s official Java tutorials offer exhaustive information on if-else statements.

Java if-else by JavaTpoint explains using if-else conditions in Java, with easy-to-understand examples.

Java if-else statement with examples by GeeksforGeeks includes a variety of examples and use cases.

In this comprehensive guide, we’ve explored the ins and outs of ‘if-else’ statements in Java, from the basics to more advanced usage scenarios.

We began with the basics, learning how to use ‘if-else’ statements to control the flow of a Java program. We then delved deeper, tackling more complex structures like nested ‘if-else’ and ‘if-else-if’ ladders. Along the way, we also discussed common issues that you might encounter when using ‘if-else’ statements and provided solutions to these problems.

We didn’t stop at ‘if-else’ statements, though. We also explored alternative approaches to control flow in Java, such as using ‘switch’ statements. We compared these methods, giving you a sense of the broader landscape of tools for managing control flow in Java.

Here’s a quick comparison of the methods we’ve discussed:

Whether you’re just starting out with Java or you’re looking to level up your control flow skills, we hope this guide has given you a deeper understanding of ‘if-else’ statements and their alternatives.

With a solid grasp of ‘if-else’ statements, you’ll be well-equipped to write Java programs that can handle complex decision-making. Happy coding!

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Gabriel Ramuglia

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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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.

• Java Arrays
• Java Strings
• Java Collection
• Java 8 Tutorial
• Java Multithreading
• Java Exception Handling
• Java Programs
• Java Project
• Java Collections Interview
• Java Interview Questions
• Spring Boot
• Java Tutorial

Overview of Java

• Introduction to Java
• The Complete History of Java Programming Language
• C++ vs Java vs Python
• How to Download and Install Java for 64 bit machine?
• Setting up the environment in Java
• How to Download and Install Eclipse on Windows?
• JDK in Java
• How JVM Works - JVM Architecture?
• Differences between JDK, JRE and JVM
• Just In Time Compiler
• Difference between JIT and JVM in Java
• Difference between Byte Code and Machine Code
• How is Java platform independent?

Basics of Java

• Java Basic Syntax
• Java Hello World Program
• Java Data Types
• Primitive data type vs. Object data type in Java with Examples
• Java Identifiers

Operators in Java

• Java Variables
• Scope of Variables In Java

Wrapper Classes in Java

Input/output in java.

• How to Take Input From User in Java?
• Scanner Class in Java
• Java.io.BufferedReader Class in Java
• Difference Between Scanner and BufferedReader Class in Java
• Ways to read input from console in Java
• System.out.println in Java
• Difference between print() and println() in Java
• Formatted Output in Java using printf()
• Fast I/O in Java in Competitive Programming

Flow Control in Java

• Decision Making in Java (if, if-else, switch, break, continue, jump)
• Java if statement with Examples
• Java if-else
• Java if-else-if ladder with Examples
• Loops in Java
• For Loop in Java
• Java while loop with Examples
• Java do-while loop with Examples
• For-each loop in Java
• Continue Statement in Java
• Break statement in Java
• Usage of Break keyword in Java
• return keyword in Java
• Java Arithmetic Operators with Examples
• Java Unary Operator with Examples
• Java Assignment Operators with Examples
• Java Relational Operators with Examples
• Java Logical Operators with Examples

Java Ternary Operator with Examples

• Bitwise Operators in Java
• Strings in Java
• String class in Java
• Java.lang.String class in Java | Set 2
• Why Java Strings are Immutable?
• StringBuffer class in Java
• StringBuilder Class in Java with Examples
• String vs StringBuilder vs StringBuffer in Java
• StringTokenizer Class in Java
• StringTokenizer Methods in Java with Examples | Set 2
• StringJoiner Class in Java
• Arrays in Java
• Arrays class in Java
• Multidimensional Arrays in Java
• Different Ways To Declare And Initialize 2-D Array in Java
• Jagged Array in Java
• Final Arrays in Java
• Reflection Array Class in Java
• util.Arrays vs reflect.Array in Java with Examples

OOPS in Java

• Object Oriented Programming (OOPs) Concept in Java
• Why Java is not a purely Object-Oriented Language?
• Classes and Objects in Java
• Naming Conventions in Java
• Java Methods

Access Modifiers in Java

• Java Constructors
• Four Main Object Oriented Programming Concepts of Java

Inheritance in Java

Abstraction in java, encapsulation in java, polymorphism in java, interfaces in java.

• 'this' reference in Java
• Inheritance and Constructors in Java
• Java and Multiple Inheritance
• Interfaces and Inheritance in Java
• Association, Composition and Aggregation in Java
• Comparison of Inheritance in C++ and Java
• abstract keyword in java
• Abstract Class in Java
• Difference between Abstract Class and Interface in Java
• Control Abstraction in Java with Examples
• Difference Between Data Hiding and Abstraction in Java
• Difference between Abstraction and Encapsulation in Java with Examples
• Difference between Inheritance and Polymorphism
• Dynamic Method Dispatch or Runtime Polymorphism in Java
• Difference between Compile-time and Run-time Polymorphism in Java

Constructors in Java

• Copy Constructor in Java
• Constructor Overloading in Java
• Constructor Chaining In Java with Examples
• Private Constructors and Singleton Classes in Java

Methods in Java

• Static methods vs Instance methods in Java
• Abstract Method in Java with Examples
• Overriding in Java
• Method Overloading in Java
• Difference Between Method Overloading and Method Overriding in Java
• Differences between Interface and Class in Java
• Functional Interfaces in Java
• Nested Interface in Java
• Marker interface in Java
• Comparator Interface in Java with Examples
• Need of Wrapper Classes in Java
• Different Ways to Create the Instances of Wrapper Classes in Java
• Character Class in Java
• Java.Lang.Byte class in Java
• Java.Lang.Short class in Java
• Java.lang.Integer class in Java
• Java.Lang.Long class in Java
• Java.Lang.Float class in Java
• Java.Lang.Double Class in Java
• Java.lang.Boolean Class in Java
• Autoboxing and Unboxing in Java
• Type conversion in Java with Examples

Keywords in Java

• Java Keywords
• Important Keywords in Java
• Super Keyword in Java
• final Keyword in Java
• static Keyword in Java
• enum in Java
• transient keyword in Java
• volatile Keyword in Java
• final, finally and finalize in Java
• Public vs Protected vs Package vs Private Access Modifier in Java
• Access and Non Access Modifiers in Java

Memory Allocation in Java

• Java Memory Management
• How are Java objects stored in memory?
• Stack vs Heap Memory Allocation
• How many types of memory areas are allocated by JVM?
• Garbage Collection in Java
• Types of JVM Garbage Collectors in Java with implementation details
• Memory leaks in Java
• Java Virtual Machine (JVM) Stack Area

Classes of Java

• Understanding Classes and Objects in Java
• Singleton Method Design Pattern in Java
• Object Class in Java
• Inner Class in Java
• Throwable Class in Java with Examples

Packages in Java

• Packages In Java
• How to Create a Package in Java?
• Java.util Package in Java
• Java.lang package in Java
• Java.io Package in Java
• Java Collection Tutorial

Exception Handling in Java

• Exceptions in Java
• Types of Exception in Java with Examples
• Checked vs Unchecked Exceptions in Java
• Java Try Catch Block
• Flow control in try catch finally in Java
• throw and throws in Java
• User-defined Custom Exception in Java
• Chained Exceptions in Java
• Null Pointer Exception In Java
• Exception Handling with Method Overriding in Java
• Multithreading in Java
• Lifecycle and States of a Thread in Java
• Java Thread Priority in Multithreading
• Main thread in Java
• Java.lang.Thread Class in Java
• Runnable interface in Java
• Naming a thread and fetching name of current thread in Java
• What does start() function do in multithreading in Java?
• Difference between Thread.start() and Thread.run() in Java
• Thread.sleep() Method in Java With Examples
• Synchronization in Java
• Importance of Thread Synchronization in Java
• Method and Block Synchronization in Java
• Lock framework vs Thread synchronization in Java
• Difference Between Atomic, Volatile and Synchronized in Java
• Deadlock in Java Multithreading
• Deadlock Prevention And Avoidance
• Difference Between Lock and Monitor in Java Concurrency
• Reentrant Lock in Java

File Handling in Java

• Java.io.File Class in Java
• Java Program to Create a New File
• Different ways of Reading a text file in Java
• Java Program to Write into a File
• Delete a File Using Java
• File Permissions in Java
• FileWriter Class in Java
• Java.io.FileDescriptor in Java
• Java.io.RandomAccessFile Class Method | Set 1
• Regular Expressions in Java
• Regex Tutorial - How to write Regular Expressions?
• Matcher pattern() method in Java with Examples
• Pattern pattern() method in Java with Examples
• Quantifiers in Java
• java.lang.Character class methods | Set 1
• Java IO : Input-output in Java with Examples
• Java.io.Reader class in Java
• Java.io.Writer Class in Java
• Java.io.FileInputStream Class in Java
• FileOutputStream in Java
• Java.io.BufferedOutputStream class in Java
• Java Networking
• TCP/IP Model
• User Datagram Protocol (UDP)
• Differences between IPv4 and IPv6
• Difference between Connection-oriented and Connection-less Services
• Socket Programming in Java
• java.net.ServerSocket Class in Java
• URL Class in Java with Examples

JDBC - Java Database Connectivity

• Introduction to JDBC (Java Database Connectivity)
• JDBC Drivers
• Establishing JDBC Connection in Java
• Types of Statements in JDBC
• JDBC Tutorial
• Java 8 Features - Complete Tutorial

Operators constitute the basic building block of any programming language. Java provides many types of operators that 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. Here are a few types: 

• 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 Ternary Operators. 

Ternary Operator in Java

Java ternary operator is the only conditional operator that takes three operands. It’s a one-liner replacement for the if-then-else statement and is used a lot in Java programming. We can use the ternary operator in place of if-else conditions or even switch conditions using nested ternary operators. Although it follows the same algorithm as of if-else statement, the conditional operator takes less space and helps to write the if-else statements in the shortest way possible.

If operates similarly to that of the if-else statement as in Exression2 is executed if Expression1 is true else Expression3 is executed.  

Example:   

Flowchart of Ternary Operation  

Examples of Ternary Operators in Java

Example 1:  .

Below is the implementation of the Ternary Operator:

Complexity of the above method:

Time Complexity: O(1) Auxiliary Space: O(1)

Example 2:  

Below is the implementation of the above method:

Implementing ternary operator on Boolean values:

Explanation of the above method:

In this program, a Boolean variable condition is declared and assigned the value true. Then, the ternary operator is used to determine the value of the result string. If the condition is true, the value of result will be “True”, otherwise it will be “False”. Finally, the value of result is printed to the console.

Advantages of Java Ternary Operator

• Compactness : The ternary operator allows you to write simple if-else statements in a much more concise way, making the code easier to read and maintain.
• Improved readability : When used correctly, the ternary operator can make the code more readable by making it easier to understand the intent behind the code.
• Increased performance: Since the ternary operator evaluates a single expression instead of executing an entire block of code, it can be faster than an equivalent if-else statement.
• Simplification of nested if-else statements: The ternary operator can simplify complex logic by providing a clean and concise way to perform conditional assignments.
• Easy to debug : If a problem occurs with the code, the ternary operator can make it easier to identify the cause of the problem because it reduces the amount of code that needs to be examined.

It’s worth noting that the ternary operator is not a replacement for all if-else statements. For complex conditions or logic, it’s usually better to use an if-else statement to avoid making the code more difficult to understand.

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