在平时的编程中，队列可以应用于很多方面。

在生活中我们同样可以随处见到它的身影，比如我们排队，先排的人先得到服务，后进来的人后接受服务。这就是队列。 说白了，就是FIFO原则（First in First out, 先进先出)。 队列的实现是基于存储结构不同而不同的，通常会有两种方式存储。线性存储或者非线行存储。

1、线性存储。是基于数组等长度固定的存储方式来实现的。我这里是先定义了一个接口，然后基于接口来实现的。

下面请看代码，

package simple;interface queue {    boolean isEmpty();    void in(Object value);    Object top();    void out();    boolean isFull();    int getSize();}public class ArrayBase implements queue {
         private static final int MAXSIZE = 100;    int front;    int rear;    int number;    Object[] data;    ArrayBase() {        front = rear = -1;        number = 0;        data = new Object[MAXSIZE];    }    @Override    public void in(Object value) {        // TODO Auto-generated method stub        if (this.isFull()) {            System.out.println("Sorry, the queue is full!");        } else {            this.rear = (this.rear + 1) % MAXSIZE;            number++;            this.data[this.rear] = value;        }    }    @Override    public Object top() {        // TODO Auto-generated method stub        if (this.isEmpty()) {            System.out.println("Sorry, the queue is empty!");        }        int p = (this.front + 1) % MAXSIZE;        return data[p];    }    @Override    public void out() {        // TODO Auto-generated method stub        if (this.isEmpty()) {            System.out.println("Sorry, the queue is empty!");        }        this.front = (this.front - 1) % MAXSIZE;        number--;    }    @Override    public boolean isFull() {        // TODO Auto-generated method stub        if (this.rear == MAXSIZE - 1) {            return true;        }        return false;    }    public boolean isEmpty() {        if (number == 0) {            return true;        }        return false;    }    @Override    public int getSize() {        // TODO Auto-generated method stub        return this.number;    }}

接下来是测试类：

package simple;public class MyQueueTest {    public static void main(String []args){        ArrayBase myQueue=new ArrayBase();        System.out.println(((ArrayBase) myQueue).isEmpty());        myQueue.in(false);        myQueue.in(1);        myQueue.in('T');        myQueue.in("Biao");        System.out.println("Now there are "+myQueue.getSize()+"  items!");        System.out.println("Top Item is: "+ myQueue.top());        myQueue.out();        System.out.println("After the out operation,there are "                            +myQueue.getSize()+" items in this queue!");    }}

然后就是我们的测试结果了：

trueNow there are 4  items!Top Item is: falseAfter the out operation,there are 3 items in this queue!

2、当然也可以使用非线性的存储结构来实现队列，好处是可以避免“假溢出”的现象，充分的利用到空间。

下面是代码实现：

package simple;interface queueListBase {    boolean isEmpty();    void in(Object value);    Object top();    Object out();    int getSize();}class Node{    Object data;    Node next;    Node(){        data=null;        next=null;    }}public class ListBase implements queueListBase{
         int number;    Node front;    Node rear;    public ListBase(){        number=0;        front=rear=null;    }    @Override    public boolean isEmpty() {        // TODO Auto-generated method stub        if(this.front==this.rear){            return true;        }        return false;    }    /*     * (non-Javadoc)此方法应该尤其要注意的是对初始时的分析     * 我就在此处忘记了front的存在，结果就会导致程序一直抱NullPointerException的错误！     * @see simple.queueListBase#in(java.lang.Object)     */    @Override    public void in(Object value) {        // TODO Auto-generated method stub        if (rear == null && front == null) {              rear = new Node();            rear.data=value;            front = rear;          } else {              Node node = new Node();            node.data=value;            rear.next = node;              rear = node;            number++;        }      }    @Override    public Object top() {        // TODO Auto-generated method stub        Node temp=new Node();        temp.data=this.front.data;        return temp;    }    @Override    public Object out() {        // TODO Auto-generated method stub        Object temp=null;        if(this.isEmpty()){            System.out.println("Sorry,the queue is Empty!");            return false;        }else{            temp=this.front.data;            this.front=this.front.next;            if(front.next==null){                this.rear=this.front;            }            number--;        }        return temp;    }    @Override    public int getSize() {        // TODO Auto-generated method stub        return number;    }}

下面是我的测试代码：

package simple;public class MyQueueTest {    public static void main(String []args){//      ArrayBase myQueue=new ArrayBase();        ListBase myQueue=new ListBase();        System.out.println(((ListBase) myQueue).isEmpty());        myQueue.in(false);        myQueue.in(1);        myQueue.in('T');        myQueue.in("Biao");        System.out.println(myQueue.out());        System.out.println(myQueue.out());        System.out.println(myQueue.out());        System.out.println(myQueue.out());        System.out.println("Now there are "+myQueue.getSize()+"  items!");        System.out.println("Top Item is: "+ myQueue.top());        myQueue.out();        System.out.println("After the out operation,there are "                            +myQueue.getSize()+" items in this queue!");    }}

下面是测试的结果：

truefalse1TSorry,the queue is Empty!falseNow there are 0  items!Top Item is: simple.Node@659e0bfdSorry,the queue is Empty!After the out operation,there are 0 items in this queue!

结果分析：

不难看出，在链式队列内存储值时，字符串类型并没有成功存储进去。但这并不代表队列无法存储字符串类型的数据，所以我们应该注意这一点！否则将会有可能导致今后软件的出错！下面是一个更加完整的非线性的队列的实现代码，也是我入队操作失败后得到纠正的一篇博客，与君共勉，共同进步吧！