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| Figure 1 - Question 1. |
|---|
class java.awt.Button
Button01class java.awt.Button
Button02class java.awt.Label
Label01class java.awt.Label
Label02 |
True or False: The code shown in Listing 2 will compile and run successfully producing the output shown in Figure 2 .
Listing 2 - Question 2.
/*File Q02.java
************************************************/import java.util.ArrayList;
import java.awt.Button;import java.awt.Label;
import java.awt.Component;public class Q02{
/*Given:
Button and Label are subclasses of the Componentclass.
The getClass method is defined in the Objectclass. When called on a reference to an object,
the method returns the name of the class fromwhich the object was instantiated.
*/public static void main(String[] args){//Create and populate a list designed to
// store references to objects of type Button// and display its contents.
ArrayList<Button>listA = new ArrayList<>();
listA.add(new Button("Button01"));listA.add(new Button("Button02"));
display(listA);System.out.println("");//blank line
//Create and populate a list designed to// store references to objects of type Label
// and display its contents.ArrayList<Label>listB = new ArrayList<>();
listB.add(new Label("Label01"));listB.add(new Label("Label02"));
display(listB);}//end main
//-------------------------------------------//static void display(
ArrayList<? extends Component>list){
for(Component n : list){System.out.println(n.getClass());
if(n instanceof Button){System.out.println(
((Button)n).getLabel());}else if(n instanceof Label) {
System.out.println(((Label)n).getText());}//end else
}//end for loop}//end display
}//end class Q02 | Figure 2 - Question 2. |
|---|
class java.awt.Button
Button01class java.awt.Button
Button02class java.awt.Label
Label01class java.awt.Label
Label02 |
True or False: The code shown in Listing 3 will compile and run successfully producing the output shown in Figure 3 .
Listing 3 - Question 3.
/*File Q03.java
************************************************/import java.util.ArrayList;
import java.awt.Button;import java.awt.Label;
import java.awt.Component;public class Q03{
/*Given:
Button and Label are subclasses of the Componentclass.
The getClass method is defined in the Objectclass. When called on a reference to an object,
the method returns the name of the class fromwhich the object was instantiated.
*/public static void main(String[] args){//Create and populate a list designed to
// store references to objects of type Button// and display its contents.
ArrayList<Button>listA = new ArrayList<>();
listA.add(new Button("Button01"));listA.add(new Button("Button02"));
display(listA);System.out.println("");//blank line
//Create and populate a list designed to// store references to objects of type Label
// and display its contents.ArrayList<Label>listB = new ArrayList<>();
listB.add(new Label("Label01"));listB.add(new Label("Label02"));
display(listB);}//end main
//-------------------------------------------//static void display(ArrayList<?>list){
for(Object n : list){System.out.println(n.getClass());
if(n instanceof Button){System.out.println(
((Button)n).getLabel());}else if(n instanceof Label) {
System.out.println(((Label)n).getText());}//end else
}//end for loop}//end display
}//end class Q03 
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