Java IdentityHashMap containsKey() Method

---

---

Description

The containsKey(Object key) method is used to test whether the specified object reference is a key in this identity hash map.

Declaration

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

public boolean containsKey(Object key)

Parameters

key − This is the possible key to be checked.

Return Value

The method call returns 'true' if the specified object reference is a key in this map.

Exception

NA

Checking Key to Exist in an IdentityHashMap of Integer, Integer Pair Example

The following example shows the usage of Java IdentityHashMap containsKey() method to check if a key is present in a Map or not. We've created a Map object of Integer,Integer pairs. 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.IdentityHashMap;

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

      // 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));
   }    
}

Output

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

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

Checking Key to Exist in an IdentityHashMap of Integer, String Pair Example

The following example shows the usage of Java IdentityHashMap containsKey() method to check if a key is present in a Map or not. We've created a Map object of Integer,String pairs. 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.IdentityHashMap;

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

      // 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));
   }    
}

Output

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

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

Checking Key to Exist in an IdentityHashMap of Integer, Object Pair Example

The following example shows the usage of Java IdentityHashMap containsKey() method to check if a key is present in a Map or not. We've created a Map object of Integer,Student pairs. 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.IdentityHashMap;

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

      // 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 + " ]";
   }
}

Output

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

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