Exercises

1. Specify the set of values and the set of operations provided by each of the following Java primitive data types:
   1. char,
   2. int,
   3. double, and
   4. String.
2. What are the features of Java that facilitate the creation of user-defined data types.
3. Explain how each of the following Java features supports polymorphism:
   1. interfaces,
   2. abstract classes, and
   3. inheritance.
4. Suppose we define two concrete classes, A and B, both of which are derived from the AbstractObject class declared in Program . Furthermore, let a and b be instances of classes A and B (respectively) declared as follows:

   public class A extends AbstractObject { ... };
   public class B extends AbstractObject { ... };
   Comparable a = new A();
   Comparable b = new B();

   Give the sequence of methods called in order to evaluate a comparison such as ``a.isLT(b)''. Is the result of the comparison true or false? Explain.
5. Consider the Int wrapper class defined in Program . Explain the operation of the following program fragment:

   Comparable i = new Int (5);
   Comparable j = new Int (7);
   boolean result = i.isLT (j);

6. Let c be an instance of some concrete class derived from the AbstractContainer class given in Program . Explain how the statement

   System.out.println (c);

   prints the contents of the container on the standard output stream.
7. Suppose we have a container c (i.e., an instance of some concrete class derived from the AbstractContainer class defined in Program ) which among other things happens to contain itself. What happens when we invoke the toString method on c?
8. Enumerations and visitors provide two ways to do the same thing--to visit one-by-one all the objects in a container. Give an implementation for the accept method of the AbstractContainer class that uses an enumeration.
9. Is it possible to implement an enumeration using a visitor? Explain.
10. Suppose we have a container which we know contains only instances of the Int class defined in Program . Design a Visitor which computes the sum of all the integers in the container.
11. Consider the following pair of Associations:

    Comparable a = new Association (new Int (3), new Integer (4));
    Comparable b = new Association (new Int (3));

    Give the sequence of methods called in order to evaluate a comparison such as ``a.isEQ(b)''. Is the result of the comparison true or false? Explain.

Copyright © 1998 by Bruno R. Preiss, P.Eng. All rights reserved.