Java - assert Keyword

assert Keyword

Java assert keyword is used to define assertion in a program. An assertion is a statement that 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 that an application primarily is for testing purposes. Assertion statements are used along with boolean expressions.

Use of assert Keyword

There are two ways in which an assert statement can be used.

First Way

assert expression;

Second Way

assert expression1 : expression2

Enable Assertion

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

java -ea Example
(or)
java -enableassertions Example

Where Example is the name of the Java file.

Example of assert Keyword

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

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);
   }
}

Output

The above example will produce the following result −

The voter's age is 14

We can disable java assertion as well using following commands

java -da Example
(or)
java -disableassertions Example

where Example is the name of the Java file.