Java TreeMap containsKey() Method

Last Updated : 16 May, 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.

Syntax of TreeMap containsKey() Method

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.

Examples of the TreeMap containsKey() Method in Java

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

// 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));
    }
}

Output

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

// 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"));
    }
}

Output

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.

TreeMap containsValue() Method in Java With Examples

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