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The Collection interface declares the following two overloaded versions of the toArray method:
public Object[] toArray()public Object[]toArray(Object[] a) In this module, will teach you how to use the first (simpler) version of the toArray method. I will also show why you need to exercise care when using the elements stored in the array to avoid corrupting the state of theobjects referred to by the elements in the collection.
I will teach you how to use the second (more complex) version of the toArray method in the next module.
The code in this series of modules is written with no thought given to Generics . As a result, if you copy and compile the code, you will probably get warnings about unchecked or unsafe operations .
While you will ultimately need to understand how to use Generics, that is a very complex topic. An understanding of Generics is beyond the scope of thiscourse. Therefore, for purposes of this course, you can simply ignore those warnings.
Let's begin with a quiz to test your prior knowledge of the Collections Framework. To take this quiz, examine the program shown in Listing 1 and write down the output produced by the program.
| Listing 1 . The program named ToArray01 . |
|---|
//File ToArray01.java
//Copyright 2001, R.G.Baldwinimport java.util.*;
import javax.swing.*;public class ToArray01{
public static void main(String args[]){
new Worker().doIt();}//end main()
}//end class ToArray01//===================================//
class Worker{public void doIt(){
Collection ref;//Create, populate, and display the
// contents of a collectionref = new LinkedList();
Populator.fillIt(ref);System.out.println("Collection contents");
showCollection(ref);//Get collection contents into the
// array and display the new// contents of the array.
Object[]array = ref.toArray();
System.out.println("New array contents");showArray(array);
//Modify a property of an object// referred to by one of the
// elements in the array. Display// array contents after
// modificationSystem.out.println("Modified array contents");
((JComponent)array[0]).setToolTipText("XX");
showArray(array);//Display the contents of the
// collectionSystem.out.println("Collection contents");
showCollection(ref);}//end doIt()
//-----------------------------------////Utility method for displaying
// array contentsvoid showArray(Object[] array){for(int i = 0; i<array.length;i++){
if(array[i]== null){
System.out.print("null ");}else{
System.out.print(((JComponent)array[i]).
getToolTipText() + " ");}//end else
}//end for loopSystem.out.println();}//end showArray()
//-----------------------------------////Utility method for displaying
// collection contentsvoid showCollection(Collection ref){
Iterator iter = ref.iterator();while(iter.hasNext()){
System.out.print(((JComponent)iter.next()).getToolTipText() + " ");
}//end while loopSystem.out.println();
}//end showCollection}// end class Worker
//===================================//class Populator{
public static void fillIt(Collection ref){ref.add(new JButton());
ref.add(new JButton());ref.add(new JLabel());
ref.add(new JButton());ref.add(new JButton());
ref.add(new JLabel());Iterator iter = ref.iterator();
int cnt = 0;JComponent refVar;
while(iter.hasNext()){refVar = (JComponent)iter.next();
if(refVar instanceof JButton){refVar.setToolTipText("B"+cnt++);
}else{refVar.setToolTipText("L" + cnt++);
}//end else}//end while loop
}//end fillIt()}//end class Populator |
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