Java HashMap containsKey() Method

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Description

The Java HashMap containsKey(Object key) method is used to check if this map contains a mapping for the specified key.

Declaration

Following is the declaration for java.util.HashMap.containsKey() method.

public boolean containsKey(Object key)

Parameters

key − This is the key whose presence in this map is to be tested.

Return Value

The method call returns 'true' if this map contains a mapping for the specified key.

Exception

NA

Check a HashMap of Integer, Integer Pair for a Key Example

The following example shows the usage of Java HashMap containsKey() method to check if a key is present in a Map or not. We've created a Map object of Integer,Integer pair. Then few entries are added, map is printed and using containsKey() we're checking about two keys in the map.

package com.tutorialspoint;

import java.util.HashMap;

public class HashMapDemo {
   public static void main(String args[]) {
      
      // create hash map
      HashMap<Integer,Integer> newmap = new HashMap<>();

      // populate hash map
      newmap.put(1, 1);
      newmap.put(2, 2);
      newmap.put(3, 3); 

      System.out.println("Initial map elements: " + newmap);
      System.out.println("Map contains 2 as key: " + newmap.containsKey(2));
      System.out.println("Map contains 4 as key: " + newmap.containsKey(4));
   }
}

Let us compile and run the above program, this will produce the following result.

Initial map elements: {1=1, 2=2, 3=3}
Map contains 2 as key: true
Map contains 4 as key: false

Check a HashMap of Integer, String Pair for a Key Example

The following example shows the usage of Java HashMap containsKey() method to check if a key is present in a Map or not. We've created a Map object of Integer,String pair. Then few entries are added, map is printed and using containsKey() we're checking about two keys in the map.

package com.tutorialspoint;

import java.util.HashMap;

public class HashMapDemo {
   public static void main(String args[]) {
      
      // create hash map
      HashMap<Integer,String> newmap = new HashMap<>();

      // populate hash map
      newmap.put(1, "tutorials");
      newmap.put(2, "point");
      newmap.put(3, "is best"); 

      System.out.println("Initial map elements: " + newmap);
      System.out.println("Map contains 2 as key: " + newmap.containsKey(2));
      System.out.println("Map contains 4 as key: " + newmap.containsKey(4));
   }
}

Let us compile and run the above program, this will produce the following result.

Initial map elements: {1=tutorials, 2=point, 3=is best}
Map contains 2 as key: true
Map contains 4 as key: false

Check a HashMap of Integer, Student Pair for a Key Example

The following example shows the usage of Java HashMap containsKey() method to check if a key is present in a Map or not. We've created a Map object of Integer,Student pair. Then few entries are added, map is printed and using containsKey() we're checking about two keys in the map.

package com.tutorialspoint;

import java.util.HashMap;

public class HashMapDemo {
   public static void main(String args[]) {
      
      // create hash map
      HashMap<Integer,Student> newmap = new HashMap<>();

      // populate hash map
      newmap.put(1, new Student(1, "Julie"));
      newmap.put(2, new Student(2, "Robert"));
      newmap.put(3, new Student(3, "Adam"));

      System.out.println("Initial map elements: " + newmap);
      System.out.println("Map contains 2 as key: " + newmap.containsKey(2));
      System.out.println("Map contains 4 as key: " + newmap.containsKey(4));
   }
}
class Student {
   int rollNo;
   String name;

   Student(int rollNo, String name){
      this.rollNo = rollNo;
      this.name = name;
   }

   @Override
   public String toString() {
      return "[ " + this.rollNo + ", " + this.name + " ]";
   }
}

Let us compile and run the above program, this will produce the following result.

Initial map elements: {1=[ 1, Julie ], 2=[ 2, Robert ], 3=[ 3, Adam ]}
Map contains 2 as key: true
Map contains 4 as key: false