java 中Collection 比较

   public class ListTest {
    private static Random random = new Random();
    public static void main(String[] args){
        ArrayList<String> arraylist = new ArrayList();
        LinkedList<String> linkedlist = new LinkedList();
        HashMap<String,Object> map = new HashMap();
        HashSet<String> set = new HashSet();
        for(int i=0;i<50000;i++){
            String r = randomString();
            arraylist.add(r);
            linkedlist.add(r);
            map.put(r, r);
            set.add(r);
        }
       
        System.out.println("arraylist size "+arraylist.size());
        System.out.println("linkedlist size "+linkedlist.size());
        System.out.println("map size "+map.size());
        System.out.println("set size "+set.size());
       
       
        System.out.println("------");
        long begin = System.currentTimeMillis();
        for(int j=0;j<arraylist.size();j++){
            arraylist.contains(arraylist.get(j));
        }
        System.out.println("arraylist time "+(System.currentTimeMillis()-begin));
       
       
        begin = System.currentTimeMillis();
        for(int j=0;j<arraylist.size();j++){
            linkedlist.contains(arraylist.get(j));
        }
        System.out.println("linkedlist time "+(System.currentTimeMillis()-begin));
       
        begin = System.currentTimeMillis();
        for(int i=0;i<100;i++){
            for(int j=0;j<arraylist.size();j++){
                map.containsKey(arraylist.get(j));
            }
        }
        System.out.println("map time "+(System.currentTimeMillis()-begin));
       
        begin = System.currentTimeMillis();
        for(int i=0;i<100;i++){
            for(int j=0;j<arraylist.size();j++){
                set.contains(arraylist.get(j));
            }
        }
        System.out.println("set time "+(System.currentTimeMillis()-begin));
       
    }
    protected static String randomString() {
        return Long.toString(random.nextLong(), 36);
    }
}
在我的机器上，结果如下：
arraylist size 50000
linkedlist size 50000
map size 50000
set size 50000
------
arraylist time 49328
linkedlist time 57641
map time 625
set time 578


可见呀，如果是在集合中查询某个对象是否存在，是HashSet的速度最快，而且比List快将近1万倍。