Revised: Sat Apr 02 20:52:01 CDT 2016
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Table of contents
Preface
This module contains review questions and answers keyed to the module titled Java3008: Abstract Methods, Abstract Classes, and Overridden Methods .
The questions and the answers are connected by hyperlinks to make it easy for you to navigate from the question to the answer and back again.
Questions
Question 1 .
True or False? The code in Listing 1 produces the output shown in Figure 1 where the two numeric values shown are random but must always match.
| Listing 1 . Source code for Java3008r.java. |
|---|
/*File Java3008r Copyright 2013, R.G.Baldwin
Rev 02/12/13*********************************************************/
import java.util.*;abstract class Java3008r{
public static void main(String[]args){
Random generator = new Random(new Date().getTime());int randomNumber = (byte)generator.nextInt();
Java3008r objRef = new Java3008rMyClass(randomNumber);System.out.println(objRef);
System.out.println(objRef.getData());System.out.println(randomNumber);
}//end main//Declare the signature of an abstract class.
public abstract int getData();}//end class Java3008r
//======================================================//class Java3008rMyClass extends Java3008r{
private int data;public Java3008rMyClass(int inData){//constructor
System.out.println("Java3008r");System.out.println("Dick");
data = inData;}//end constructor
public int getData(){//overridden abstract methodreturn data;
}//end getData()}//end class Java3008rMyClass |
.
| Figure 1 . Possible output from the code in Listing 1 . |
|---|
Java3008r
DickBaldwin
-80-80 |
Question 2
True or False? The purpose of an abstract method declaration is to establish the signature of a method that must be overridden in a (non-abstract) subclass of the class in which the abstract method is declared.
Question 3
True or False? When an abstract method is executed, it always exhibits default behavior defined in the class in which it is declared.
Question 4
True or False? An abstract method must be overridden in a subclass in order to be executed.
Question 5
True or False? An abstract method can be overridden once and once only and it must be overridden in the immediate subclass of the class in which it isdeclared.
Question 6
True or False? The existence of an abstract method in a superclass guarantees that objects instantiated from every (non-abstract) subclass of that superclass will have a concrete (executable) version of a method having that same signature.
Question 7
True or False? Any class can be declared abstract. The consequence of declaring a class abstract is that it is not possible to instantiate an objectof the class.