CIS 121 February 10, 2000

There will be no quiz today so you may use your time today to work on your programming assignments and ask questions. You should be nearing completion since the program is due tomorrow.

Before beginning, there is an exercise we would like to demonstrate.

Examining the access control keywords

Go to the directory c:\java.

Create two subdirectories. One called test and the other called test1.

Enter test.

Create the following two files.

A.java

package test;

import USA.*;

public class A {
   public int a;
   private int b;
   protected int c;
   int f;

   public A() {
      a = 1;
      b = 2;
      c = 3;
   }
}

B.java

package test;

import USA.*;

public class B extends A {
   public int d;

   public B() {
      d=4;
   }

   public void showValues() {
      System.out.println("The value of a is " + a);
      System.out.println("The value of b is " + b);
      System.out.println("The value of c is " + c);
      System.out.println("The value of f is " + f);
   }

   public static void main(String[] args) {
      B myB = new B();
      myB.showValues();
   }
}

Enter c:\java\test1 and create the following file.

C.java

package test1;

import USA.*;
import test.*;

public class C {

   public static void main(String[] args) {
      A myA = new A();
      System.out.println("The value of a is " + myA.a);
      System.out.println("The value of b is " + myA.b);
      System.out.println("The value of c is " + myA.c);
      System.out.println("The value of f is " + myA.f);
   }
}

Enter c:\java\test.

Compile A.java. There shouldn't be any errors.

However, when you compile B.java, there will be errors.

Before compiling B.java, examine the use of the variables, and determing which line(s) will cause compile time error(s).

Then compile B.java to test your answer.

What do you learn from this exercise?

Enter c:\java\test1.

When you try to compile C.java there will be errors.

Before compiling C.java, examine the code, and determine which line(s) will cause compile time error(s).

Then compile C.java to test your answer.

What do you learn from this exercise?

The above exercises should give you a better understanding of what the access control variables mean.

You may use the rest of this laboratory period to ask questions regarding your assignment.

CIS 121 February 10, 2000

Use your time wisely since the program is due in less than 24 hours!!!!!