Java Map containsKey() - Check if Key Exists in Map

If you want to check whether the specified key is present in the HashMap or not you can use containsKey() method in the java.util.Map which returns true only if Map contains a mapping for the specified key.

Syntax of the method is as given below.

containsKey(Object key)

key- key whose presence in this map is to be tested

Method returns true if this map contains a mapping for the specified key otherwise returns false.

containsKey() Java example

1. Here we have a map of items with item and its price as key, value pairs. If you want to check if the specified key is already there or not.

import java.util.HashMap;
import java.util.Map;

public class ContainsKeyDemo {

  public static void main(String[] args) {
    Map<String, Integer> itemMap = new HashMap<>();
    itemMap.put("Trousers", 1200);
    itemMap.put("Shirt", 800);
    itemMap.put("Shoes", 2400);
    itemMap.put("Belt", 750);
    
    if(itemMap.containsKey("Shoes")) {
      System.out.println("Item already present in the Map");
    }
  }
}

Output

Item already present in the Map

2. You can also use containsKey() method to add a new entry to the Map after checking that the key is already not there.

import java.util.HashMap;
import java.util.Map;

public class ContainsKeyDemo {

  public static void main(String[] args) {
    Map<String, Integer> itemMap = new HashMap<>();
    itemMap.put("Trousers", 1200);
    itemMap.put("Shirt", 800);
    itemMap.put("Belt", 750);  
    
    boolean isItemShoeExist = itemMap.containsKey("Shoes");
    System.out.println("Does key Shoes exist in the HashMap- " + isItemShoeExist);
    
    if(!itemMap.containsKey("Shoes")) {
      itemMap.put("Shoes", 2400);      
    }else {
      System.out.println("Item already present in the Map");
    }
    System.out.println("Map Values- " + itemMap);
  }
}

Output

Does key Shoes exist in the HashMap- false
Map Values- {Shirt=800, Belt=750, Shoes=2400, Trousers=1200}

As you can see when checking for the key which is not present in the Map, containsKey method returns false. Using that you can add a new entry to the HashMap.

That's all for this topic Java Map containsKey() - Check if Key Exists in Map. If you have any doubt or any suggestions to make please drop a comment. Thanks!

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