Introduction to List and Queue Interface
List Interface :
The List interface extends the Collection
interface to define an ordered collection. It is also known as the sequence
collection which permits duplicates element to accommodate in the set but does not map a
key value to an object. It permits one or more elements to be null.
This interface adds position-oriented operations
such as insert an element, get an element as well as remove
or change an element based on their numerical position in the list.
It also performs search operation to allow searching a specified object in the
list and returns its numerical position.
In addition to methods
of the Set interface, it provides following three methods shown in
the table below:
|
Method
|
Uses
|
|
get(
)
|
Returns
the element at the specified index position in this collection
|
|
listIterator(
)
|
Returns a
List Iterator object for the collection which may then be used to retrieve
an object
|
|
remove(
)
|
Removes
the element at the specified index position in this collection
|
Queue Interface:
A Queue interface extends the Collection
interface to define an ordered collection for holding elements in a
FIFO (first-in-first-out) manner to process them i.e. in a FIFO queue the
element that is inserted firstly will also get removed first.
Besides basic collection operations, queues also provide
additional operations such as insertion, removal, and inspection
.
The Methods of this interface are as follows.
|
Method
|
Uses
|
|
peek(
)
|
Returns an
element but if queue is empty then it returns null
|
|
poll(
)
|
Removes an
element but returns null if the queue is empty.
|
In the Java platform, Collections Framework provides
three general-purpose List and Queue implementation-classes:
ArrayList
LinkedList
RunArrayList
The following program demonstrates the implementation
of List and Queue interfaces.
import java.util.*;
public class ListQueueDemo {
public static void main(String args[]) {
int numbers[]={34, 22,10,60,30};
List <Integer>list = new ArrayList<Integer>();
try{
for(int i=0; i<5; i++){
list.add(numbers[i]);
}
System.out.println("the List is: ");
System.out.println(list);
LinkedList <Integer>queue = new LinkedList<Integer>();
for(int i=0; i<5; i++){
queue.addFirst(numbers[i]);
}
System.out.println("The Oueue is: ");
System.out.println(queue);
queue.removeLast();
System.out.println("After removing last element the queue is: "+ queue);
}
catch(Exception e){}
}
}
|
Output of the Program:
C:\nisha>javac ListQueueDemo.java
C:\nisha>java ListQueueDemo
the List is:
[34, 22, 10, 60, 30]
The Oueue is:
[30, 60, 10, 22, 34]
After removing last element the queue is:
[30, 60, 10, 22]
C:\nisha> |
This program creates a List and Queue, and
inserts a
group of numbers in these lists. The program than
prints out the list of numbers in the set. The addFirst( ) and removeLast(
) methods add and remove an element in a FIFO manner, i.e. the first
element of the queue is removed first .
Download this Program:
|
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