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Revised: Sat Apr 02 20:52:01 CDT 2016
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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.
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 |
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| Figure 1 . Possible output from the code in Listing 1 . |
|---|
Java3008r
DickBaldwin
-80-80 |
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.
True or False? When an abstract method is executed, it always exhibits default behavior defined in the class in which it is declared.
True or False? An abstract method must be overridden in a subclass in order to be executed.
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.
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.
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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