| << Chapter < Page | Chapter >> Page > |
| Figure 5 - Question 5. |
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class java.awt.Frame
class java.awt.Frameclass java.awt.Window
class java.awt.Windowclass javax.swing.JFrame
class javax.swing.JFrame |
True or False: The code shown in Listing 6 will compile and run successfully producing the output shown in Figure 6 .
Listing 6 - Question 6.
/*File Q06.java
************************************************/import java.util.ArrayList;
import java.awt.Window;import java.awt.Frame;
import javax.swing.JFrame;public class Q06{
/*Given:
Component extends ObjectContainer extends Component
Window extends ContainerFrame extends Window
JFrame extends FrameThe getClass method is defined in the Object
class. When called on a reference to an object,the method returns the name of the class from
which the object was instantiated.*/
public static void main(String[]args){
Frame frame0 = new Frame("Frame0");ArrayList<Frame>listA = new ArrayList<>();
listA.add(frame0);listA.add(new Frame("Frame1"));
display(listA);ArrayList<Window>listB = new ArrayList<>();
listB.add(new Window(frame0));listB.add(new Window(frame0));
display(listB);ArrayList<JFrame>listC = new ArrayList<>();
listC.add(new JFrame("JFrame0"));listC.add(new JFrame("JFrame1"));
display(listC);}//end main
//-------------------------------------------//static void display(
ArrayList<? super Frame>list){
for(Object n : list){System.out.println(n.getClass());
}//end for loopSystem.out.println();//blank line
}//end display}//end class Q06 | Figure 6 - Question 6. |
|---|
class java.awt.Frame
class java.awt.Frameclass java.awt.Window
class java.awt.Windowclass javax.swing.JFrame
class javax.swing.JFrame |
What is the meaning of the following two images?
These images were inserted here simply to insert some space between the questions and the answers to keep them from being visible on the screen at thesame time.
This image was also inserted for the purpose of inserting space between the questions and the answers.
False. This program attempts to illustrate the use of a lower bounded wildcard to define a generic method that will accept an incoming reference to anobject of a generic class where the parameter type for the object is equal to or above the type of the wildcard in the inheritance hierarchy. The lower boundedwildcard type for the display method is Frame. Therefore, the display method will accept references to ArrayList objects for parameter types Frame, Window,Container, Component, or Object, but it will not accept a reference to an ArrayList object for parameter type JFrame. Therefore, the program will notcompile, resulting in the error shown in Figure 7 .
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