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Java if-else Statement

In Java, the if statement is a conditional statement used to execute a block of code when a specified condition evaluates to true. If the condition is false, an optional else statement can be used to execute an alternative block of code.

The if statement in Java checks a Boolean expression and executes a specific block of code only if the condition is true.

The if-else statement allows Java programs to handle both true and false conditions. If the condition inside the if statement evaluates to false, the else block is executed instead.

Using if-else statements in Java improves decision-making in programs by executing different code paths based on conditions.

Following is the syntax of an if...else statement −

if(Boolean_expression) {
   // Executes when the Boolean expression is true
}else {
   // Executes when the Boolean expression is false
}

If the boolean expression evaluates to true, then the if block of code will be executed, otherwise else block of code will be executed.

Below is the flowchart of the if-else statement, illustrating how it works:

In this example, we're showing the usage of if else statement. We've created a variable x and initialized it to 30. Then in the if statement, we're checking x with 20. As if statement is false, the statement within the else block is executed.

public class Test {

   public static void main(String args[]) {
      int x = 30;

      if( x < 20 ) {
         System.out.print("This is if statement");
      }else {
         System.out.print("This is else statement");
      }
   }
}

When the above code is compiled and executed, it produces the following result −

This is else statement

The if...else if...else statement is used for executing multiple code blocks based on the given conditions (Boolean expressions).

An if statement can be followed by an optional else if...else statement, which is very useful to test various conditions using a single if...else if statement.

When using if-else if- else statements there are a few points to keep in mind.

• An if can have zero or one else's and it must come after any else if's.

• An if can have zero to many else if's and they must come before the else.

• Once an else if succeeds, none of the remaining else if's or else's will be tested.

Following is the syntax of an if...else if...else statement −

if(Boolean_expression 1) {
   // Executes when the Boolean expression 1 is true
}else if(Boolean_expression 2) {
   // Executes when the Boolean expression 2 is true
}else if(Boolean_expression 3) {
   // Executes when the Boolean expression 3 is true
}else {
   // Executes when the none of the above condition is true.
}

In this example, we're showing the usage of if...else if...else statement. We've created a variable x and initialized it to 30. Then in the if statement, we're checking x with 10. As if statement is false, control jumps to else if statement checking another value with x and so on.

public class Test {

   public static void main(String args[]) {
      int x = 30;

      if( x == 10 ) {
         System.out.print("Value of X is 10");
      }else if( x == 20 ) {
         System.out.print("Value of X is 20");
      }else if( x == 30 ) {
         System.out.print("Value of X is 30");
      }else {
         System.out.print("This is else statement");
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Value of X is 30

In this example, we're showing the usage of if...else if...else statement. We've created a variable x and initialized it to 30.0. Then in the if statement, we're checking x with 10,0. As if statement is false, control jumps to else if statement checking another value with x and so on.

public class Test {

   public static void main(String args[]) {
      double x = 30.0;

      if( x == 10.0 ) {
         System.out.print("Value of X is 10.0");
      }else if( x == 20.0 ) {
         System.out.print("Value of X is 20.0");
      }else if( x == 30.0 ) {
         System.out.print("Value of X is 30.0");
      }else {
         System.out.print("This is else statement");
      }
   }
}

When the above code is compiled and executed, it produces the following result −

Value of X is 30.0

The nested if else statement is used for better decision-making when other conditions are to be checked when a given condition is true. In the nested if else statement, you can have an if-else statement block the another if (or, else) block.

Below is the syntax of nested if else statement:

if(condition1){    
	// code block    
	if(condition2){  
		//code block
	}    
}

The following examples finds the largest number among three using nested if..else statement.

public class Test {

    public static void main(String[] args) {

        int x = 10, y = 20, z = 30;

        if(x >= y) {
            if(x >= z)
                System.out.println(x + " is the largest.");
            else
                System.out.println(z + " is the largest.");
        } else {
            if(y >= z)
                System.out.println(y + " is the largest.");
            else
                System.out.println(z + " is the largest.");
        }
    }
}

When the above code is compiled and executed, it produces the following result −

30 is the largest.

The if-else statement in Java is useful for making decisions based on conditions. Below are some common use cases:

• User Authentication: If-else statements are used to check whether a username and password match the stored credentials before granting access.
• Age Verification: They help determine if a user is eligible for certain actions, such as voting, driving, or accessing age-restricted content.
• Even or Odd Number Check: By using an if-else statement, a program can check whether a number is even or odd and execute the corresponding logic.
• Grading System: If-else conditions can assign letter grades based on numerical scores, such as assigning "A" for scores above 90 and "B" for scores between 80 and 89.
• Leap Year Check: The if-else statement is used to determine whether a given year is a leap year based on divisibility rules.
• Discount Calculation: It helps apply discounts based on purchase amounts, such as giving a 10% discount for orders above $100.
• Traffic Light Simulation: If-else statements can control traffic signals by checking the current state and switching between red, yellow, and green accordingly.

The if-else statement in Java follows specific rules to ensure proper execution. Below are the key rules:

• Boolean Expression Required: The condition inside an if statement must be a Boolean expression that evaluates to true or false.
• Curly Braces for Multiple Statements: If there is more than one statement inside if or else, enclose them within { } curly braces.
• Single Statement Optional Braces: If there is only one statement inside if or else, curly braces are optional but recommended for better readability.
• Else is Optional: The else block is not mandatory; an if statement can exist without an else.
• Else Without If is Invalid: The else statement must always be associated with a preceding if statement.
• Nested if-else Allowed: You can place an if or else if statement inside another if statement (nested if-else).
• Multiple else-if Conditions: The else if condition can be used multiple times before the final else statement.
• Execution Order: Java executes the if-else conditions from top to bottom, and once a condition is met, the remaining conditions are ignored.

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