Java if

Summary: in this tutorial, you will learn how to use the Java if statement to evaluate a boolean expression and execute a block of code if the expression is true.

Introduction to the Java if statement

The if statement is a basic control flow construct in Java. The if statement evaluates a condition and executes a block of code if the condition is true.

Here’s the syntax of the if statement:

if(condition) {
   // code to execute if the condition is true
}Code language: Java (java)

In this syntax:

• The if is the keyword that marks the beginning of the if statement.
• The condition located within the parentheses () is a boolean expression that evaluates to true or false.
• The curly braces {} enclose the block of code to be executed if the condition is true.

But if the condition is false, Java will skip the code block and continue with the next statement after the if statement.

Note that the curly brace {} is optional if you have one statement to execute. However, it’s a good practice to always include the curly braces even if you have a single statement.

Java if statement examples

Let’s take some examples of using Java if statement.

1) A simple Java if statement example

The following example illustrates how to use the if statement:

public class App {
    public static void main(String[] args) {
        int temperature = 38;
        if (temperature > 32) {
            System.out.println("It's hot!");
        }
    }
}Code language: Java (java)

Output:

It's hot!Code language: Java (java)

In this example, we have an integer variable temperature with a value of 38.

The if statement checks if the temperature is greater than 32. Because this condition is true, the program will display the message "It's hot!".

2) Using the if statement with a relational operator ==

The following example uses an if statement to check if a number is an even number using an arithmetic operator % and a relational operator ==:

public class App {
    public static void main(String[] args) {
        int number = 20;
        if(number % 2 == 0){
            System.out.println("The number is even.");
        }
    }
}Code language: Java (java)

Output:

The number is even.Code language: Java (java)

In this example, we have an integer variable number with a value of 20.

Because the expression number % 2 returns the remainder of the division, the whole expression number % 2 == 0 is true if the remainder is zero or false otherwise.

In other words, if the condition number % 2 == 0 is true, the number is an even number. The program displays the message "The number is even." because the condition is true.

3) Using the if statement with a logical operator

The following example uses an if statement with the logical operator AND (&&) to check if a person can drive:

public class App {
    public static void main(String[] args) {
        byte age = 17;
        boolean hasDrivingLicense = true;

        if (age >= 16 && hasDrivingLicense) {
            System.out.println("You can drive.");
        }
    }
}Code language: Java (java)

In this example, we have a variable age with a value of 17 and a variable hasDrivingLicense with the value of true.

The condition age >= 16 && hasDrivingLicense returns true if the age is greater than 16 and hasDrivingLicense is true.

Because the condition is true, the program displays the message "You can drive.".

Nested if statement

Java allows you to nest an if statement inside another if statement like this:

if (condition1) {
   if(condition2) {
      // ...
   }
}Code language: Java (java)

In this syntax, we have an outer if statement containing an inner if statement.

If condition1 is true, Java will execute the code block enclosed within the curly braces {}. If condition1 is false, Java will skip the code block and the program continues to the next statement after the outer if statement.

The inner if statement checks another condition condition2. If the condition2 is true, Java executes the code block inside the curly braces of the inner if statement.

In other words, the code block inside the inner if statement only executes if both condition1 and condition2 are true.

The following example illustrates how to use a nested if statement:

public class App {
    public static void main(String[] args) {
        byte age = 17;
        boolean hasDrivingLicense = true;

        if (age >= 16) {
            System.out.println("You are of legal age.");

            if (hasDrivingLicense) {
                System.out.println("You can drive.");
            }
        }
    }
}Code language: Java (java)

How it works

• The outer if statement checks if age is greater than or equal to 18 (legal age). If it’s true, it prints "You are of legal age" and proceeds to the inner if statement.
• The inner if statement checks if hasDrivingLicense is true (the person has a driver’s license).
• If both conditions are met, it prints "You can drive." But if age is less than 18 or hasLicense is false, the inner if statement is skipped.

In practice, you should avoid using nested if statement because it makes the code harder to read and maintain.

Summary

• Use Java if statement to execute a block of code if a condition is true.