hashMap的三种遍历方式

    public void testClass(){        HashMap<String, String> hashMap = new HashMap<String, String>();        hashMap.put("1", "1");        hashMap.put("2", "2");        Set<Entry<String, String>> entrySet = hashMap.entrySet();        Iterator<Entry<String, String>> iterator = entrySet.iterator();        //1.迭代器实现 效率高        while(iterator.hasNext()){            Entry<String, String> entry = iterator.next();            String key = entry.getKey();            System.out.println(key);            String value = entry.getValue();            System.out.println(value);        }        //2.entrySet        for (Entry<String, String> entry : entrySet) {            System.out.println(entry.getKey() + ":" + entry.getValue());        }        //3.keySet        Set<String> keySet = hashMap.keySet();        for (String entry : keySet) {            System.out.println(hashMap.get(entry));        }    }