How to use Assertion ?

Usage of assertion

• to validate the program

We can use assertions on internal, control flow and class invariants as well to improve the programming experience.

Example

Scanner scanner = new Scanner( System.in );

System.out.print( "Enter a number between 0 and 20: " );

int value = scanner.nextInt();

assert( value >= 0 && value <= 20 ) :

         System.out.printf( "You have entered %d\n", value );

To enable assertion at runtime , -ea option is used

java -ea AssertionExample

Output

Enter a number between 0 and 20:  4

You have entered 4

Enter a number between 0 and 20:  21

AssertionError will be thrwon by JVM