How to determine whether key exists in map collection in java?

Java method to determine whether the specified key exists in the map collection: 1. Use the containsKey() method to determine; if it exists, it returns true, if it does not exist, it returns false. 2. Use loop traversal, compare one by one, and make judgments.

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In java, sometimes you will encounter the map passed by the judgment Whether the specified key is included, there are two methods:

Method 1: Loop through and compare one by one

HashMap map = new HashMap();  
map.put("1", "value1");  
map.put("2", "value2");  
Iterator keys = map.keySet().iterator(); 
while(keys.hasNext()){  
     String key = (String)keys.next();
     if("2".equals(key)){  
        System.out.println("存在key");  
     }  
}

Method 2: Directly Use the containsKey()

#map provided by the java api. Map is a collection of key-value pairs of key and value. If there are key and value pairs, there will be a way to determine whether there is a key. This method is the containsKey method. <br/>

boolean flag=map.containsKey("opt")

For example:

if(map.containsKey("name")){
value=map.get("name").toString();
System.out.println("找到了name的值："+value);
}

The containsKey(key) method in map can determine whether the key is in the map There is presence. Returns true if exists. Returns false if it does not exist.

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