Java 25 (LTS) reference · Map and HashMap Methods

Java Map containsKey() Method

Return true if the map has an entry for the key, even when its value is null. O(1) for HashMap.

Java 25 (LTS) Since Java 1.0

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Syntax

map.containsKey(key)

Parameters

Parameter	Description
`key` Object	The key to check.

Return value

true or false.

Examples

containsKey() vs get() != null

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Map<String, String> settings = new HashMap<>();
        settings.put("theme", null);
        System.out.println(settings.containsKey("theme"));
        System.out.println(settings.get("theme") != null);
    }
}

Output

true
false

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Username checks

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Map<String, Integer> users = Map.of("ana", 1);
        System.out.println(users.containsKey("ana") ? "taken" : "available");
        System.out.println(users.containsValue(1));
    }
}