public class Main {

  public static void main(String[] args) {

    // Enable assertions

    ClassLoader loader = ClassLoader.getSystemClassLoader();

    loader.setDefaultAssertionStatus(true);

    // Run the assert example

    AssertExample example = new AssertExample();

    example.run();

  }

}

​

class AssertExample {

  public void run() {

    int a = 12;

    try {

      assert a == 12; // Assertion without a fail message

      assert a == 12 : "a is not 12";

      assert a == 15 : "a is not 15";

    } catch (AssertionError e) {

      System.out.println(e.getMessage());

    }

  }

}

​