java hashmap key exists

To check if a key exists in a HashMap in Java, you can use the containsKey method of the HashMap class.

Here is an example of how to check if a key exists in a HashMap:

HashMap<String, Integer> map = new HashMap<>();
map.put("apple", 1);
map.put("banana", 2);
map.put("orange", 3);

if (map.containsKey("apple")) {
    // the key "apple" exists in the map
}
if (!map.containsKey("pear")) {
    // the key "pear" does not exist in the map
}

In this example, the map variable is a HashMap object that maps strings to integers. The containsKey method returns true if the map contains an element with the specified key, and false otherwise.

You can also use the get method of the HashMap class to check if a key exists in the map.

For example:

if (map.get("apple") != null) {
    // the key "apple" exists in the map
}
if (map.get("pear") == null) {
    // the key "pear" does not exist in the map
}

The get method returns the value of the element with the specified key, or null if the key is not present in the map.

Note that the containsKey method is faster than the get method for checking if a key exists in the map, because it does not need to retrieve the value of the element. However, the get method can be useful if you also need to retrieve the value of the element at the same time.