Java Assertions

//new assert statement & keyword in Java 1.4
//compile with -source 1.4 flag
//run with -ea flag


public class TestAssertions {
    
    static boolean goodHalOpen = true;
    static boolean badHalOpen = false;
    
    static boolean openPodDoor = false;
    
    //set up assertion test
    static void testPodDoor() {
       //note: in the assert statement, 
       //  the expression before the colon is evaluated and
       //  a false will make the assert throw a
       //  java.lang.AssertionError.  
       //The expression after the colon (if there is one) 
       //  will be added to the output
       //  text when the AssertionError is thrown.
	
       assert openPodDoor : "bad Hal";
       
       System.out.println("after assertion");       
       System.out.println(" ");
    }


    public static void main(String[] args) {
        
       System.out.println("test one");
       openPodDoor = goodHalOpen;
       testPodDoor();
       
       System.out.println("test two");
       openPodDoor = badHalOpen;
       testPodDoor();   
       
    }
}

javac -source 1.4 TestAssertions.java


java -ea TestAssertions

test one
after assertion


test two
Exception in thread "main" java.lang.AssertionError: 
  bad Hal at TestAssertions.testPodDoor 
    (TestAssertions.java:19)
      at TestAssertions.main(TestAssertions.java:33)