Queue定义，直接copyJava的Queue，去除了Collection接口。
public interface Queue<E> {
/**
* Inserts the specified element into this queue if it is possible to do so
* immediately without violating capacity restrictions, returning
* {@code true} upon success and throwing an {@code IllegalStateException}
* if no space is currently available.
*
* @param e the element to add
* @return {@code true} (as specified by
* @throws IllegalStateException if the element cannot be added at this
* time due to capacity restrictions
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this queue
* @throws NullPointerException if the specified element is null and
* this queue does not permit null elements
* @throws IllegalArgumentException if some property of this element
* prevents it from being added to this queue
*/
boolean add(E e);
/**
* Inserts the specified element into this queue if it is possible to do
* so immediately without violating capacity restrictions.
* When using a capacity-restricted queue, this method is generally
* preferable to {@link #add}, which can fail to insert an element only
* by throwing an exception.
*
* @param e the element to add
* @return {@code true} if the element was added to this queue, else
* {@code false}
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this queue
* @throws NullPointerException if the specified element is null and
* this queue does not permit null elements
* @throws IllegalArgumentException if some property of this element
* prevents it from being added to this queue
*/
boolean offer(E e);
/**
* Retrieves and removes the head of this queue. This method differs
* from {@link #poll poll} only in that it throws an exception if this
* queue is empty.
*
* @return the head of this queue
* @throws NoSuchElementException if this queue is empty
*/
E remove();
/**
* Retrieves and removes the head of this queue,
* or returns {@code null} if this queue is empty.
*
* @return the head of this queue, or {@code null} if this queue is empty
*/
E poll();
/**
* Retrieves, but does not remove, the head of this queue. This method
* differs from {@link #peek peek} only in that it throws an exception
* if this queue is empty.
*
* @return the head of this queue
* @throws NoSuchElementException if this queue is empty
*/
E element();
/**
* Retrieves, but does not remove, the head of this queue,
* or returns {@code null} if this queue is empty.
*
* @return the head of this queue, or {@code null} if this queue is empty
*/
E peek();
}
ArrayQueue
public class ArrayQueue implements Queue {
// 数组
int[] array;
//最大值
int maxSize;
// 前
int front;
// 后
int rear;
static final float DEFAULT_LOAD_FACTOR = 0.75f;
public ArrayQueue(int maxSize) {
this.front = -1;
this.rear = -1;
this.array = new int[maxSize];
this.maxSize = maxSize;
}
@Override
public boolean add(Object value) {
reset();
if (isFull()) {
throw new IllegalArgumentException("queue if full, can not add!");
}
addDirectly(value);
return true;
}
@Override
public boolean offer(Object value) {
reset();
if (isFull()) {
System.out.println("queue if full, can not offer!");
return false;
}
addDirectly(value);
return true;
}
@Override
public Object remove() {
if (isEmpty()) {
throw new NoSuchElementException("queue if empty!");
}
return getDirectly();
}
@Override
public Object poll() {
if (isEmpty()) {
return null;
}
return getDirectly();
}
@Override
public Object element() {
if (isEmpty()) {
throw new NoSuchElementException("queue if empty!");
}
return array[front + 1];
}
@Override
public Object peek() {
if (isEmpty()) {
return null;
}
return array[front + 1];
}
private boolean isEmpty() {
return rear == front;
}
private void addDirectly(Object value) {
this.array[++rear] = (int) value;
}
private int getDirectly() {
++front;
int value = array[front];
array[front] = 0;
return value;
}
private boolean isFull() {
if (this.rear == maxSize -1) {
return true;
}
return false;
}
/**
* 重置队列,希望可以有多余的空间
*/
private void reset() {
if (rear + 1 > maxSize * DEFAULT_LOAD_FACTOR) {
if (front != -1) {
int index = -1;
int[] temp = new int[maxSize];
for (int i = front + 1; i <= rear; i++) {
temp[++index] = this.array[i];
}
this.array = temp;
this.rear = this.rear - front - 1;
this.front = -1;
}
}
}
public static void main(String[] args) throws Exception {
ArrayQueue queue = new ArrayQueue(2);
Scanner scanner = new Scanner(System.in);
while(true) {
System.out.println("o(offer)");
System.out.println("p(poll)");
char cmd = scanner.next().charAt(0);
switch (cmd) {
case 'o' :
System.out.println("请输入值需要添加的值....");
int value = scanner.nextInt();
queue.offer(value);
System.out.println(String.format("queue is : %s", Arrays.toString(queue.array)));
break;
case 'p' :
System.out.println(String.format("value is : %s", queue.poll()));
System.out.println(String.format("queue is : %s", Arrays.toString(queue.array)));
break;
default:
System.out.println("未知的命令" + cmd);
break;
}
}
}
}