Java简单实现固定长度队列（FIFO）

/* * To change this template, choose Tools | Templates * and open the template in the editor. */package linkedlisttest;import java.util.ArrayList;import java.util.Deque;import java.util.LinkedList;import java.util.List;/** * * @author Vicky.H * @email [e-mail] */public class FIFOTest {    /**     * @param args the command line arguments     */    public static void main(String[] args) {        FIFO<A> fifo = new FIFOImpl<A>(5);        for (int i = 0; i < 20; i++) {            A a = new A("A:" + i);            A head = fifo.addLastSafe(a);            System.out.println(i + "\thead:" + head + "\tsize:" + fifo.size());        }        System.out.println("---------------");        System.out.println("弹出数据");        List<A> polls = fifo.setMaxSize(3);        for (A a : polls) {            System.out.println("\thead:" + a);        }                System.out.println("剩余数据");        for (A a : fifo) {            System.out.println("\thead:" + a);        }        System.out.println(fifo.size());    }}interface FIFO<T> extends List<T>, Deque<T>, Cloneable, java.io.Serializable {    /**     * 向最后添加一个新的，如果长度超过允许的最大值，则弹出一个 *     */    T addLastSafe(T addLast);    /**     * 弹出head，如果Size = 0返回null。而不同于pop抛出异常     * @return      */    T pollSafe();    /**     * 获得最大保存     *     * @return     */    int getMaxSize();    /**     * 设置最大存储范围     *     * @return 返回的是，因为改变了队列大小，导致弹出的head     */    List<T> setMaxSize(int maxSize);}class FIFOImpl<T> extends LinkedList<T> implements FIFO<T> {    private int maxSize = Integer.MAX_VALUE;    private final Object synObj = new Object();    public FIFOImpl() {        super();    }    public FIFOImpl(int maxSize) {        super();        this.maxSize = maxSize;    }    @Override    public T addLastSafe(T addLast) {        synchronized (synObj) {            T head = null;            while (size() >= maxSize) {                head = poll();            }            addLast(addLast);            return head;        }    }    @Override    public T pollSafe() {        synchronized (synObj) {            return poll();        }    }    @Override    public List<T> setMaxSize(int maxSize) {        List<T> list = null;        if (maxSize < this.maxSize) {            list = new ArrayList<T>();            synchronized (synObj) {                while (size() > maxSize) {                    list.add(poll());                }            }        }        this.maxSize = maxSize;        return list;    }    @Override    public int getMaxSize() {        return this.maxSize;    }}class A {    private String name;    public A() {    }    public A(String name) {        this.name = name;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    @Override    public String toString() {        return "A{" + "name=" + name + '}';    }}

run:
0 head:null size:1
1 head:null size:2
2 head:null size:3
3 head:null size:4
4 head:null size:5
5 head:A{name=A:0} size:5
6 head:A{name=A:1} size:5
7 head:A{name=A:2} size:5
8 head:A{name=A:3} size:5
9 head:A{name=A:4} size:5
10 head:A{name=A:5} size:5
11 head:A{name=A:6} size:5
12 head:A{name=A:7} size:5
13 head:A{name=A:8} size:5
14 head:A{name=A:9} size:5
15 head:A{name=A:10} size:5
16 head:A{name=A:11} size:5
17 head:A{name=A:12} size:5
18 head:A{name=A:13} size:5
19 head:A{name=A:14} size:5
---------------
弹出数据
 head:A{name=A:15}
 head:A{name=A:16}
剩余数据
 head:A{name=A:17}
 head:A{name=A:18}
 head:A{name=A:19}
3
成功构建 (总时间: 0 秒)