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CSCI 305: Programming Languages

Java Part 3

Reading: Webster Ch. 17

Instructions

1. Watch This Video - (26:44)
2. Watch This Video - (33:24)
3. Watch This Video - (08:14)
4. Review the Lecture Slides
5. Review the Example Code
6. Complete the Out of Class Exercise
7. Check Your Learning
8. Attend Class and Complete the In Class Exercises
9. Check Your Learning
10. Example Code

Out of Class Exercise

Work on Exercise 17.2 from the book (It’s a bit too long to put here)

Check Your Learning:

Solution:

In Class Exercises

Exercise 1

The behavior of the try statement in Java can be rather complicated, since the try block, the catch block, and the finally block can all finish their execution in different ways. For each of the following scenarios, what happens? Write simple test programs in Java to demonstrate the answers to the following questions about the behavior of finally. Include your program, its output, and your conclusions for each part.

1. The try block completes normally, and the finally block completes normally.

        System.out.println("1");
        try {
            System.out.println("2");
        } catch (Exception e) {
            System.out.println("3");
        } finally {
            System.out.println("4");
        }
   

   Output:

   1
   2
   4
   

As expected the finally block executes.

1. The try block stops by throwing an exception that is not caught, and the finally block stops by throwing a different exception.

        System.out.println("1");
        try {
            System.out.println("2");
            throw new RuntimeException();
        } catch (NullPointerException e) {
            System.out.println("3");
        } finally {
            System.out.println("4");
            throw new ArithmeticException();
        }
   

   Output:

   1
   2
   4
   Exception in thread "main" java.lang.ArithmeticException
    at TryCatchEx.main(TryCatchEx.java:12)
   

As expected the only exception propagated was the ArithmeticException.

1. The try block stops by throwing an exception that is caught, the relevant catch block completes normally, and the finally block stops by throwing an exception.

        System.out.println("1");
        try {
            System.out.println("2");
            throw new RuntimeException();
        } catch (RuntimeException e) {
            System.out.println("3");
        } finally {
            System.out.println("4");
            throw new ArithmeticException();
        }
   

Output:

1
2
3
4
Exception in thread "main" java.lang.ArithmeticException
	at TryCatchEx.main(TryCatchEx.java:12)

As expected the try, catch, and finally executed in order with the last line execute the ArithmeticException being thrown.

1. The try block stops by throwing an exception that is caught, the relevant catch block stops by throwing a different exception, and the finally block stops by executing an explicit return statement.

        System.out.println("1");
        try {
            System.out.println("2");
            throw new RuntimeException();
        } catch (RuntimeException e) {
            System.out.println("3");
            throw new IllegalArgumentException();
        } finally {
            System.out.println("4");
            return;
        }
   

Output:

1
2
3
4

1. The try block stops by throwing an exception that is caught, the relevant catch block stops by executing an explicit return statement, and the finally block stops by executing an explicit return statement, returning a different value.

        System.out.println("1");
        try {
            System.out.println("2");
            throw new RuntimeException();
        } catch (RuntimeException e) {
            System.out.println("3");
            return 0;
        } finally {
            System.out.println("4");
            return -1;
        }
   

Output:

1
2
3
4
-1

As expected the actual returned value was that returned from the finally block, as finally is always executed.

1. The try block stops by executing an explicit return statement, and the finally block stops by throwing an exception.

        System.out.println("1");
        try {
            System.out.println("2");
            return 0;
        } catch (RuntimeException e) {
            System.out.println("3");
            return 0;
        } finally {
            System.out.println("4");
            throw new ArithmeticException();
        }
   

Output:

1
2
4
Exception in thread "main" java.lang.ArithmeticException
	at TryCatchEx.x(TryCatchEx.java:17)
	at TryCatchEx.main(TryCatchEx.java:4)

As expected the last line execute was the throwing of the ArithmeticException and the two return statements were disregarded.