====== Lab 9 ======

~~NOTOC~~

** CS203 ** \\
** Spring 2013 ** \\
** Apr 5 **


===== Goals =====

  * Experiment with types and subtypes



===== Activities =====

  - Launch Netbeans, and create a new project named **//lab9//** under your ''cs203'' course directory
    * make the main class ''Examples'' rather than the default
  - Add the ''tester.jar'' file to your project's Libraries
  - Add an ''A'' class and a ''B'' class to your project, and copy/paste the respective code below:  <code java>
/**
 * cs203
 * Spring 2013
 * Lab 9
 * 
 * file: B.java
 */

public class B {

    public void bmethod1() {
        System.out.println("class B: bmethod1() called...");
    }

    public void bmethod2() {
        System.out.println("class B: bmethod2() called, calling which class's bmethod1?...");
        bmethod1();
    }
}

/**
 * cs203
 * Spring 2013
 * Lab 9
 * 
 * file: A.java
 */

public class A extends B {

    @Override
    public void bmethod1() {
        System.out.println("class A: bmethod1() called...");
    }
}
</code>
  - Add code to the ''main()'' method in your ''Examples'' class to experiment with classes ''A'' and ''B''. Your code should generate the following output when run: <code text>
run:
Initializing myB, an object of type B, to an instance of type B...
class B: bmethod1() called...
class B: bmethod2() called, which class's bmethod1() will I call???
class B: bmethod1() called...

Initializing myB, and object of type B, to an instance of type A...
class A: bmethod1() called...
class B: bmethod2() called, which class's bmethod1() will I call???
class A: bmethod1() called...
BUILD SUCCESSFUL (total time: 0 seconds)
</code>
  - Notice how this is a way to exploit the behavior of B type objects. Malicious coders could potentially do bad things in class A's ''bmethod1''.
  - One way to protect the behavior of B objects is to make class B final: <code java>
public final class B { 
</code> Make class B final and observe what happens when you try to compile your code. Discuss with Marc or one of our coaches.

===== Submit your lab =====

  * When you've had enough fun, submit your work using the submit203 script: \\ ''submit203 lab9 lab9''


===== When you've had enough (for today) =====

  * Logout and have a good weekend!