Implements a Queue (FIFO) with linked-list. - Java Data Structure

Java examples for Data Structure:List

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Description

Implements a Queue (FIFO) with linked-list.

Demo Code

import static java.lang.System.out;

import java.util.Iterator;
import java.util.NoSuchElementException;

public class Queue<Item> implements Iterable<Item> {

    private Node first, last;
    /*from ww  w .  j a  va2s  . co m*/
    private class Node {
        private Item item;
        private Node next;
    }
  
    public boolean isEmpty() {
        return first == null;
    }
    
    public void enqueue(Item item) {
        Node oldlast = last;
        last = new Node();
        last.item = item;
        last.next = null;
        
        if (isEmpty())
            first = last;
        else
            oldlast.next = last;
    }
    
    public Item dequeue() {
        Item item = first.item;
        first = first.next;
        
        if (isEmpty()) 
            last = null;
    
        return item;
    }
    
    /**
     * Implements a iterator for Queue, using FIFO.
     * 
     * <h5>Lecture: Iterators (Week 2)</h5>
     */
    private class QueueIterator implements Iterator<Item> {
        
        private Node current = first;
        
        public boolean hasNext() {
            return current != null;
        }
        
        public Item next() {
            if (!hasNext())
                throw new NoSuchElementException();
            
            Item item = current.item;
            current = current.next;
            return item;
        }
        
        public void remove() {
            throw new UnsupportedOperationException();
        }
    }
  
    @Override
    public Iterator<Item> iterator() {
        return new QueueIterator();
    }

    public static void main(String[] args) {
      Queue<String> queue = new Queue<String>();
      queue.enqueue("E");
      queue.enqueue("X");
      queue.enqueue("A");
      queue.enqueue("M");
      queue.enqueue("P");
      queue.enqueue("L");
      queue.enqueue("E");
      
        for (String s: queue) {
            out.printf("%s ",s);
        }
    }
}

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