事例代码如下：

package com.yonge.test;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class Test {

    /**
     * @param args
     */
    public static void main(String[] args) {
        List<String> list = new ArrayList<String>();
        list.add("aaa");
        list.add("bbb");
        list.add("ccc");
        list.add("aaa");
        list.add("ddd");
        System.out.print("List:");
        for (String str : list) {
            System.out.print(str + "  ");
        }
        System.out.println();
        Set<String> set = new HashSet<String>(list);
        System.out.print("Set:");
        for (String str : set) {
            System.out.print(str + "  ");
        }
    }

}

 运行结果：

List:aaa  bbb  ccc  aaa  ddd  
Set:aaa  ddd  ccc  bbb