Java Map. Containskey() method: judge whether the map collection object contains the specified key name

containsKey(Object key)

Typical application

public static void main(String[] args){
  Map map = new HashMap();  //定义Map对象
  map.put("apple","新鲜的苹果");  //向集合中添加对象
  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());
  String key = "book";
  boolean contains=map.containsKey(key);  //判断是否包含指定的键值
  if(contains){  //如果条件为真
    System.out.println("在Map集合中包含键名"+key);  //输出信息
  }else{
    System.out.println("在Map集合中不包含键名"+key);
  }
}