Java Map. Keyset() method: get all the key names of the map set

keySet()

Typical application

public static void main(String[] args){
    Map map = new HashMap();  //定义Map集合
    map.put("apple","新鲜的苹果");  //向集合中添加元素
    map.put("computer","配置优良的计算机");
    map.put("book","堆积成山的图书");
    map.put("time",new Date());  //向集合中添加时间对象
    Set keySet = map.keySet();  //获取key集合对象
    for(Object keyName:keySet){
    System.out.println("键名:"+keyName);  //输出键名
  }
}