Java Collections unmodifiableMap() Method

---

---

Description

The Java Collections unmodifiableMap() method is used to return an unmodifiable view of the specified map.

Declaration

Following is the declaration for java.util.Collections.unmodifiableMap() method.

public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K,? extends V> m)

Parameters

m − This is the map for which an unmodifiable view is to be returned.

Return Value

• The method call returns an unmodifiable view of the specified map.

Exception

NA

Getting Immutable Map From a Mutable Map of String, Integer Example

The following example shows the usage of Java Collection unmodifiableMap(Map) method. We've created a Map object of String and Integer. Few entries are added and then using unmodifiableMap(Map) method, we've retrieved the immutable version of map and printed the map.

package com.tutorialspoint;

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

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

      // populate the map
      map.put("1",1); 
      map.put("2",2);
      map.put("3",3);

      // create a immutable map
      Map<String,Integer> immutableMap = Collections.unmodifiableMap(map);

      System.out.println("Immutable map is :"+immutableMap);
   }
}

Output

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

Immutable map is :{1=1, 2=2, 3=3}

Getting Immutable Map From a Mutable Map of String, String Example

The following example shows the usage of Java Collection unmodifiableMap(Map) method. We've created a Map object of String and String. Few entries are added and then using unmodifiableMap(Map) method, we've retrieved the immutable version of map and printed the map.

package com.tutorialspoint;

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

public class CollectionsDemo {
   public static void main(String[] args) {
      
      // create map
      Map<String,String> map = new HashMap<String,String>();

      // populate the map
      map.put("1","TP"); 
      map.put("2","IS");
      map.put("3","BEST");

      // create a immutable map
      Map<String,String> immutableMap = Collections.unmodifiableMap(map);

      System.out.println("Immutable map is :"+immutableMap);
   }
}

Output

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

Immutable map is :{1=TP, 2=IS, 3=BEST}

Getting Immutable Map From a Mutable Map of String, Object Example

The following example shows the usage of Java Collection unmodifiableMap(Map) method. We've created a Map object of String and Student object. Few entries are added and then using unmodifiableMap(Map) method, we've retrieved the immutable version of map and printed the map.

package com.tutorialspoint;

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

public class CollectionsDemo {
   public static void main(String[] args) {
      
      // create map
      Map<String,Student> map = new HashMap<String,Student>();

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

      // create a immutable map
      Map<String,Student> immutableMap = Collections.unmodifiableMap(map);

      System.out.println("Immutable map is :"+immutableMap);
   }
}
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.

Immutable map is :{1=[ 1, Julie ], 2=[ 2, Robert ], 3=[ 3, Adam ]}