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This module contains review questions and answers keyed to the module titled Java3008: Abstract Methods, Abstract Classes, and Overridden Methods.

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

Answer 1

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.

Answer 2

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.

Answer 3

Question 4

True or False? An abstract method must be overridden in a subclass in order to be executed.

Answer 4

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.

Answer 5

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.

Answer 6

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.

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Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
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