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Java TreeMap containsKey() Method - GeeksforGeeks

Last Updated : 11 Jul, 2025

The containsKey() method in Java is used to check if a given key exists in a TreeMap. If the key is present in the map, it returns true, otherwise, it returns false. This method is very helpful when we need to verify whether a mapping exists before performing any operation on it.

treeMap.containsKey(key);

• Parameter: key: This is the key whose mapping is supposed to be checked inside a map.
• Return Value: The method returns boolean true if the presence of the key is detected else false.

Example 1: In this example, we are going to use a TreeMap with Integer keys and String values. We will check the presence of keys using the containsKey() method.

// Java program to demonstrate 
// TreeMap containsKey() method
import java.util.TreeMap;

public class Geeks {
    
    public static void main(String[] args) {
        
        // Create a TreeMap with Integer keys
        TreeMap<Integer, String> tm = new TreeMap<>();

        // Add key-value pairs
        tm.put(10, "Geeks");
        tm.put(15, "4");
        tm.put(20, "Geeks");
        tm.put(25, "Welcomes");
        tm.put(30, "You");

        System.out.println("Initial Mappings are: " + tm);

        // Check if key 20 is present
        System.out.println("Is the key '20' present? " 
        + tm.containsKey(20));

        // Check if key 5 is present
        System.out.println("Is the key '5' present? " 
        + tm.containsKey(5));
    }
}

Initial Mappings are: {10=Geeks, 15=4, 20=Geeks, 25=Welcomes, 30=You}
Is the key '20' present? true
Is the key '5' present? false

Example 2: In this example, we are going to create a TreeMap with String keys and Integer values. Here, we will check for the existence of some string keys.

// Java program to demonstrate 
// TreeMap containsKey() method
import java.util.TreeMap;

public class Geeks {
    
    public static void main(String[] args) {
        
        // Create a TreeMap with String keys
        TreeMap<String, Integer> tm = new TreeMap<>();

        // Add key-value pairs
        tm.put("Geeks", 10);
        tm.put("4", 15);
        tm.put("Geeks", 20); 
        tm.put("Welcomes", 25);
        tm.put("You", 30);

        System.out.println("Initial Mappings are: " + tm);

        // Check if key is present
        System.out.println("Is the key 'Welcomes' present? " 
        + tm.containsKey("Welcomes"));

        System.out.println("Is the key 'World' present? " 
        + tm.containsKey("World"));
    }
}

Initial Mappings are: {4=15, Geeks=20, Welcomes=25, You=30}
Is the key 'Welcomes' present? true
Is the key 'World' present? false

Important Points:

• This method checks whether a particular key present or not in the map.
• This method works with all types of keys that is Integer, String, etc.
• This method is very useful for avoiding NullPointerExceptions or for validating keys before updates.
• If there are duplicate keys are added, the latest value will overwrite the old one, but the key will still be present.

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