Assertions in Java

An assertion is a statement in Java which ensures the correctness of any assumptions which have been done in the program. When an assertion is executed, it is assumed to be true. If the assertion is false, the JVM will throw an Assertion error. It finds it application primarily in the testing purposes. Assertion statements are used along with boolean expressions.

Assertions in Java can be done with the help of the assert keyword. There are two ways in which an assert statement can be used.

First Way −

assert expression;

Second Way −

assert expression1 : expression2

By default, assertions are disabled in Java. In order to enable them we use the following command −

java -ea Example
java -enableassertions Example

where Example is the name of the Java file.

Let us see an example for generation of an assertion error by the JVM −


 Live Demo

public class Example {
   public static void main(String[] args) {
      int age = 14;
      assert age <= 18 : "Cannot Vote";
      System.out.println("The voter's age is " + age);


The voter's age is 14