Lab 9

CS203
Spring 2013
Apr 5

Goals

Activities

  1. Launch Netbeans, and create a new project named lab9 under your cs203 course directory
    • make the main class Examples rather than the default
  2. Add the tester.jar file to your project’s Libraries
  3. Add an A class and a B class to your project, and copy/paste the respective code below: 
    /**
 * 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...");
    }
}

  4. 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: 

    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)

  5. 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.
  6. One way to protect the behavior of B objects is to make class B final: 

    public final class B {

    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

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