Java Collections unmodifiableSet() Method

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Description

The Java Collections unmodifiableSet() method Returns an unmodifiable view of the specified set.

Declaration

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

public static <T> boolean addAll(Collection<? super T> c, T.. a)

Parameters

s − This is the set for which an unmodifiable view is to be returned.

Return Value

The method call returns an unmodifiable view of the specified set.

Exception

NA

Getting Immutable Set From a Mutable Set of Integer Example

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

package com.tutorialspoint;

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

public class CollectionsDemo {
   public static void main(String[] args) {
      
      // create set
      Set<Integer> set = new HashSet<Integer>();

      // populate the set
      set.add(1); 
      set.add(2);
      set.add(3);

      // create a immutable set
      Set<Integer> immutableSet = Collections.unmodifiableSet(set);

      System.out.println("Immutable set is :"+immutableSet);
   }
}

Output

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

Immutable set is :[1, 2, 3]

Getting Immutable Set From a Mutable Set of String Example

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

package com.tutorialspoint;

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

public class CollectionsDemo {
   public static void main(String[] args) {
      
      // create set
      Set<String> set = new HashSet<String>();

      // populate the set
      set.add("TP"); 
      set.add("IS");
      set.add("BEST");

      // create a immutable set
      Set<String> immutableSet = Collections.unmodifiableSet(set);

      System.out.println("Immutable set is :"+immutableSet);
   }
}

Output

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

Immutable set is :[IS, BEST, TP]

Getting Immutable Set From a Mutable Set of Object Example

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

package com.tutorialspoint;

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

public class CollectionsDemo {
   public static void main(String[] args) {
      
      // create set
      Set<Student> set = new HashSet<Student>();

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

      // create a immutable set
      Set<Student> immutableSet = Collections.unmodifiableSet(set);

      System.out.println("Immutable set is :"+immutableSet);
   }
}
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 set is :[[ 1, Julie ], [ 2, Robert ], [ 3, Adam ]]