// hashMap的遍历 
    public void testHashMap() { 
        Map<String, String> map = new HashMap<String, String>(); 
        for (int i = 1; i < 100001 ; i++) { 
            map.put(String.valueOf(i), "value1"); 
        } 
 
        //第一种：普遍使用，二次取值 
        System.out.println("通过Map.keySet遍历key和value："); 
        long t1 = System.currentTimeMillis(); 
        for (String key : map.keySet()) { 
            System.out.println("key= " + key + " and value= " + map.get(key)); 
        } 
        long t2 = System.currentTimeMillis(); 
 
        //第二种 
        System.out.println("通过Map.entrySet使用iterator遍历key和value："); 
        long t3 = System.currentTimeMillis(); 
        Iterator<Map.Entry<String, String>> it = map.entrySet().iterator(); 
        while (it.hasNext()) { 
            Map.Entry<String, String> entry = it.next(); 
            System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue()); 
        } 
        long t4 = System.currentTimeMillis(); 
 
        //第三种：推荐，尤其是容量大时 
        System.out.println("通过Map.entrySet遍历key和value"); 
        long t5 = System.currentTimeMillis(); 
        for (Map.Entry<String, String> entry : map.entrySet()) { 
            System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue()); 
        } 
        long t6 = System.currentTimeMillis(); 
 
        //第四种 
        System.out.println("通过Map.values()遍历所有的value，但不能遍历key"); 
        long t7 = System.currentTimeMillis(); 
        for (String v : map.values()) { 
            System.out.println("value= " + v); 
        } 
        long t8 = System.currentTimeMillis(); 
        long t12 = t2 - t1; 
        long t34 = t4 - t3; 
        long t56 = t6 - t5; 
        long t78 = t8 - t7; 
        System.out.println("--------总耗费时间----------"); 
        System.out.println(t12); 
        System.out.println(t34); 
        System.out.println(t56); 
        System.out.println(t78); 
    }