Java Tutorial - Java If

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Java if statement is used to execute a block of code based on a condition.

Java If Statement

The following the simplest form of Java if statement:

if(condition) 
   statement;

condition is a boolean expression. If condition is true, then the statement is executed.

If condition is false, then the statement is bypassed.

The following code outputs a message based on the value of an integer. It uses the if statement to do the check.

public class Main {
/*from   w w w  .j av a 2s . c om*/
  public static void main(String args[]) {
    int num = 99;
    if (num < 100) {
      System.out.println("num is less than 100");

    }
  }
}

The output generated by this program is shown here:

Example

If statement is often used to to compare two variables. The following code defines two variables, x and y, the it uses the if statement to compare them and prints out messages.

public class Main {
//  w  w  w  .  j  ava 2s . c  om
  public static void main(String args[]) {
    int x, y;

    x = 10;
    y = 20;

    if (x < y){
      System.out.println("x is less than y");
    }

    x = x * 2;
    if (x == y){
      System.out.println("x now equal to y");
    }

    x = x * 2;
    if (x > y){
      System.out.println("x now greater than y");
    }

    if (x == y){
      System.out.println("===");
    }
  }
}

The output generated by this program is shown here:

Example 2

We can also use a boolean value to control the if statement. The value of a boolean variable is sufficient, by itself, to control the if statement.

public class Main {
  public static void main(String args[]) {
    boolean b;//from   www .ja  v  a  2s.  c om
    b = false;
    if (b) {
      System.out.println("This is executed.");
    } else {
      System.out.println("This is NOT executed.");
    }

  }
}

There is no need to write an if statement like this:

if(b == true) ...

The output generated by this program is shown here:

Java if else Statement

The if statement is a conditional branch statement. We can add else statement to the if statement.

Here is the general form of the if-else statement:

if (condition) 
   statement1; 
else 
   statement2;

The else clause is optional. Each statement may be a single statement or a compound statement enclosed in curly braces (a block). Only one statement can appear directly after the if or the else. To include more statements, you'll need to create a block, as in this fragment.

The following example shows how to use Java if else statement.

 
public class Main {
  public static void main(String[] argv) {
    int i = 1;//from   w w w  .  j  a v a 2  s.  c o m

    if (i > 0) {
      System.out.println("Here");
      i -= 1;

    } else
      System.out.println("There");
  }
}
  ]]>

The output:

It is good to include the curly braces when using the if statement, even when there is only one statement in each clause.

Java if else ladder statement

The if else ladder statement is used to work on multiple conditions.

The if-else-if Ladder looks like this:

if(condition) 
   statement; 
else if(condition) 
   statement; 
else if(condition) 
   statement; 
. 
.
else 
   statement;

Here is a program that uses an if-else-if ladder.

 
public class Main {
  public static void main(String args[]) {
    int month = 4;
    String value;/*  ww  w  .j  a va  2s.  c om*/
    if (month == 1 )
      value = "A";
    else if (month == 2)
      value = "B";
    else if (month == 3)
      value = "C";
    else if (month == 4)
      value = "D";
    else
      value = "Error";

    System.out.println("value = " + value);
  }
}

Here is the output produced by the program:

Java nested if statement

A nested if is an if statement inside another another if statement or else.

The following code uses a nested if statement to compare values.

 
public class Main {
  public static void main(String[] argv) {
    int i = 10;/*from w ww .  java  2s .  c o m*/
    int j = 4;
    int k = 200;
    int a = 3;
    int b = 5;
    int c = 0;
    int d =0;
    if (i == 10) {
      if (j < 20){
        a = b;
      }
      if (k > 100){
        c = d;
      }
      else{
        a = c;
      }
    } else{
      a = d;
    }
    System.out.println("a = " + a);
    System.out.println("b = " + b);
    System.out.println("c = " + c);
    System.out.println("d = " + d);
    
  }
}

The output:

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