Java if..else..if


There are two types of decision making statements in Java. They are:

  • if statements
  • if else statements
  • if...else if...else Statement
  • switch statements

The if Statement

An if statement consists of a Boolean expression followed by one or more statements.

Syntax

if(Boolean_expression)
{
   //Statements will execute if the Boolean expression is true
}

If the Boolean expression evaluates to true then the block of code inside the if statement will be executed. If not the first set of code after the end of the if statement (after the closing curly brace) will be executed.

Example

public class Test {

   public static void main(String args[]){
      int x = 10;

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

The if...else Statement

An if statement can be followed by an optional else statement, which executes when the Boolean expression is false.

Syntax

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

Example

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");
      }
   }
}
Output
This is else statement

The if...else if...else Statement

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

When using if , else if , else statements there are 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.

Syntax

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.
}

Example

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");
      }
   }
}
Output
Value of X is 30

Nested if...else Statement

It is always legal to nest if-else statements which means you can use one if or else if statement inside another if or else if statement.

Syntax

if(Boolean_expression 1){
   //Executes when the Boolean expression 1 is true
   if(Boolean_expression 2){
      //Executes when the Boolean expression 2 is true
   }
}

Example

public class Test {

   public static void main(String args[]){
      int x = 30;
      int y = 10;

      if( x == 30 ){
         if( y == 10 ){
             System.out.print("X = 30 and Y = 10");
          }
       }
    }
}
Output
X = 30 and Y = 10

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