How to determine whether the key exists in map in java

The method for map in java to determine whether a key exists: 1. Judge through [containsKey("key")]; 2. Judge through the [hasNext()] method, the code is [Set set = map. keySet();].

The operating environment of this tutorial: windows7 system, java10 version, DELL G3 computer. This method is suitable for all brands of computers.

How to determine whether the key exists in map in java:

Method 1:

Through containsKey(" key") to judge, for example:

  Map<String,String> map= new HashMap<String,String>();
    map.put("key","value");
    boolean isEmpty=map.containsKey("key");

Method 2:

Use the hasNext() method to judge, for example:

Set set = map.keySet();
Iterator it = set.iterator();
//通过判断是否存在下一个，来遍历map集合
while (it.hasNext()) {
}

or

Iterator it= map.entrySet().iterator();
//通过判断是否存在下一个，来遍历map集合
while (it.hasNext()) {
}

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