Map的四种遍历方式

public static void main(String[] args) {
	Map<String, String> map = new HashMap<String, String>();
	map.put("1", "value1");
	map.put("2", "value2");
	map.put("3", "value3");

	//第一种：普遍使用，二次取值
	System.out.println("通过Map.keySet遍历key和value：");
	for (String key : map.keySet()) {
		System.out.println("key= "+ key + " and value= " + map.get(key));
	}

	//第二种
	System.out.println("通过Map.entrySet使用iterator遍历key和value：");
	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());
	}

	//第三种：推荐，尤其是容量大时
	System.out.println("通过Map.entrySet遍历key和value");
	for (Map.Entry<String, String> entry : map.entrySet()) {
		System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
	}

	//第四种
	System.out.println("通过Map.values()遍历所有的value，但不能遍历key");
	for (String v : map.values()) {
		System.out.println("value= " + v);
	}
}