Java if Statement

In this chapter you will learn:

1. What is Java If Statement
2. Syntax for Java If Statement
3. Example - for Java If Statement
4. Example - If statement and comparison operators
5. Example - If statement and single boolean variable

Description

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

Syntax

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.

Example

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  a va 2 s .  co m
  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 2

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 {
//ww  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 3

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   ww  w . j a  v  a2  s  .  c  o m
    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:

Next chapter...

What you will learn in the next chapter:

1. What is Java if else Statement
2. Syntax for Java if else Statement
3. Example - Java if else statement

Java if Statement