Map的遍历有两种方式

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public void test2(){
Map<String, Integer> map = new HashMap<String, Integer>();
map.put("zhangsan", 1000);
map.put("lisi", 2000);
map.put("wangwu", 3000);
//方式一
Set<Map.Entry<String, Integer>> entrySet = map.entrySet();
for(Map.Entry<String, Integer> m:entrySet){
System.out.println(m.getKey()+","+m.getValue());
} System.out.println("-----------------");
//方式二
Set<String> keys = map.keySet();
for(String key:keys){
System.out.println(map.get(key));
}

}

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);
  }

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