Java队列的两种实现方式

package Algorithm.learn;import java.util.Arrays;/**
* Created by liujinhong on 2017/3/7.
*/
public class ArrayQueue<E> {
Object[] queue;
int size; public ArrayQueue() {
queue = new Object[10];
} public boolean isEmpty() {
return size == 0;
} public E poll() {
if (isEmpty()) return null;
E data = (E) queue[0];
System.arraycopy(queue, 1, queue, 0, size-1);
size--;
return data;
} private void ensureCapacity(int size) {
if (size > queue.length) {
int len = queue.length + 10;
queue = Arrays.copyOf(queue, len);
}
} public void offer(E data) {
ensureCapacity(size+1);
queue[size++] = data;
} public static void main(String[] args) {
ArrayQueue<Integer> queue = new ArrayQueue<>(); for (int i = 0; i < 20; i++) {
queue.offer(i);
} for (int i = 0; i < 20; i++) {
System.out.println(queue.poll());
}
}
}

package Algorithm.learn;/**
* Created by liujinhong on 2017/3/7.
* 基于链表实现队列
*/
public class ListQueue<E> {
class Node<E> {
Node<E> next = null;
E data;
public Node(E data) {
this.data = data;
}
} private Node<E> head = null;
private Node<E> tail = null; public boolean isEmpty() {
return head == null;
} public void offer(E e) {
Node<E> node = new Node<E>(e);
if (isEmpty()) {
head = node;
tail = node;
return;
}
tail.next = node;
tail = node;
} public E poll() {
if (isEmpty()) return null;
E data = head.data;
head = head.next;
return data;
} public int size() {
Node<E> temp = head;
int len = 0;
while (temp != null) {
len++;
temp = temp.next;
}
return len;
} public static void main(String[] args) {
ListQueue<String> queue = new ListQueue<>();
queue.offer("a");
queue.offer("b"); System.out.println(queue.poll());
System.out.println(queue.poll());
}
}