双Buffer切换的一个Java小实验

BufferTest.java

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;


public class BufferTest {

    private static volatile List<String> list = new ArrayList<String>();

    public static void init() {
        for (int i = 0; i < 10; i++) {
            list.add(i + " " + i);
        }
    }

    public static void switchList() {
        List<String> list2 = new ArrayList<String>();
        for (int i = 3; i < 7; i++) {
            list2.add(i + " " + i);
        }
        list = list2;
        System.out.println("new list.size() = " + list.size());
    }

    public static void readList() throws Exception {
        int count = 0;

        // foreach使用的是iterator，开始循环时已经确定堆内存的地址，中间更换不影响其遍历原有数组
        // for (String s : list) {
        // Thread.sleep(1000);
        // System.out.println(s + " list.size() = " + list.size());
        // count++;
        // }

        // Iterator获得数组的地址之后，与原数组就没有关系了，原数组引用变了循环依然遍历的是原数组.
        Iterator<String> i = list.iterator();
        while (i.hasNext()) {
            Thread.sleep(1000);
            System.out.println(i.next() + " list.size() = " + list.size());
        }

        // 直接for循环使用list.get每次调用都可能切换到新的list上，加上volatile可以保证可见性.
        // for (int i = 0; i < list.size(); i++) {
        // Thread.sleep(1000);
        // System.out.println(list.get(i));
        // count++;
        // }

        System.out.println("elements count = " + count);
    }

    public static void main(String[] args) throws Exception {
        init();
        new Thread(new Runnable() {

            public void run() {
                System.out.println("start thead 1");
                try {
                    readList();
                } catch (Exception e) {
                    e.printStackTrace();
                }
                System.out.println("end thead 1");
            }
        }).start();

        Thread.sleep(5000);

        new Thread(new Runnable() {

            public void run() {
                System.out.println("start thead 2");
                try {
                    System.out.println("begin to switch ...");
                    switchList();
                    System.out.println("switch finished ! ");
                } catch (Exception e) {
                    e.printStackTrace();
                }
                System.out.println("end thead 2");
            }
        }).start();
    }
}