Java简单实现固定长度队列（FIFO）

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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)