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If you wrote down the following for the program output, you already understand most of the material covered in this module and you can probably skipthis module and move on to the next module.
Collection data
Joe Bill Tom JOE BILL TOMRaw array data
Joe Bill Tom JOE BILL TOMNatural order sorted array data
BILL Bill JOE Joe TOM TomCustom order sorted array data
Tom TOM Joe JOE Bill BILLCollection data
Joe Bill Tom JOE BILL TOM If you didn't write down the correct output for the program in Listing 1 , you should probably continue with your study of this module.
Although this program is somewhat more complex, the overall structure of this program is similar to programs that I have discussed in previous modules.Therefore, I will concentrate on those aspects of this program that differentiate it from the programs in previous modules.
The code in Listing 2 instantiates a new object of the Vector class and stores a reference to that object in the variable named ref .
| Listing 2 . A new Vector object. |
|---|
ref = new Vector(); |
The Vector class was part of Java long before the Collections Framework was released. However, with the release of the Collections Framework,the Vector class was upgraded to implement the Collection interface and the List interface.
Therefore, a Vector is a List , and adheres to the various contracts of the List interface. For example, since it is not a Set , it doesn't prohibit duplicate elements. Because it is a List , it is an ordered collection. The position of each element in the collection is determined by a numeric index associated with the element and is independent ofthe value of the element.
As has been the case in several of the programs in previous modules, the code in Listing 3 passes the Vector object's reference to a method named fillIt where the Vector is populated with the names of several people.
| Listing 3 . Call the fillIt method. |
|---|
Populator.fillIt(ref); |
The code for the fillIt method is shown in Listing 4 . As you can see, the names were added to the collection in no particular order relative to theirvalues. (The add method for the Vector class simply adds each new element to the end of the list.)
| Listing 4 . The fillIt method. |
|---|
class Populator{
public static void fillIt(Collection ref){
ref.add("Joe");ref.add("Bill");
ref.add("Tom");ref.add("JOE");
ref.add("BILL");ref.add("TOM");
}//end fillIt()}//end class Populator |
When an iterator is used to traverse the elements in a Vector collection, the elements are delivered by the iterator in ascending index order,beginning with the element stored at index 0.
The code in Listing 5 gets and uses an iterator to display the contents of the populated collection.
| Listing 5 . Iteration on a Vector. |
|---|
iter = ref.iterator();
System.out.println("Collection data");while(iter.hasNext()){
System.out.print(iter.next() + " ");}//end while loop |
The code in Listing 5 produces the following output:
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