Collections.shuffle

就是随机打乱原来的顺序，和洗牌一样。如：

// ShuffleTest.java

import java.util.*;

public class ShuffleTest {
    public static void main(String[] args) {
        List<Integer> list = new ArrayList<Integer>();
        for (int i = 0; i < 10; i++)
            list.add(new Integer(i));
        System.out.println("打乱前:");
        System.out.println(list);

        for (int i = 0; i < 5; i++) {
            System.out.println("第" + i + "次打乱：");
            Collections.shuffle(list);
            System.out.println(list);
        }
    }
}