Java Collections unmodifiableList() Method

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Description

The Java Collections unmodifiableList() method is used to returns an unmodifiable view of the specified list.

Declaration

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

public static <T> List<T> unmodifiableList(List<? extends T> list)

Parameters

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

Return Value

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

Exception

NA

Getting Immutable List From a Mutable List of Integer Example

The following example shows the usage of Java Collection unmodifiableList(List) method. We've created a List object with some integers. Using unmodifiableList(List) method, we've retrieved the immutable version of list and printed the list.

package com.tutorialspoint;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class CollectionsDemo {

   public static void main(String[] args) {
      List<Integer> list = new ArrayList<>(Arrays.asList(1,2,3,4,5));
	  
      // immutable version of list
      List<Integer> c = Collections.unmodifiableList(list);
      System.out.println("Immutable list: "+ c);
   }
}

Output

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

Immutable list: [1, 2, 3, 4, 5]

Getting Immutable List From a Mutable List of String Example

The following example shows the usage of Java Collection unmodifiableList(List) method. We've created a List object with some strings. Using unmodifiableList(List) method, we've retrieved the immutable version of list and printed the list.

package com.tutorialspoint;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class CollectionsDemo {

   public static void main(String[] args) {
      List<String> list = new ArrayList<>(Arrays.asList("Welcome","to","Tutorialspoint"));

      // immutable version of list
      List<String> c = Collections.unmodifiableList(list);
      System.out.println("Immutable list: "+ c);
   }
}

Output

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

Immutable list: [Welcome, to, Tutorialspoint]

Getting Immutable List From a Mutable List of Object Example

The following example shows the usage of Java Collection unmodifiableList(List) method. We've created a List object with some Student objects. Using unmodifiableList(List) method, we've retrieved the immutable version of list and printed the list.

package com.tutorialspoint;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class CollectionsDemo {

   public static void main(String[] args) {
      List<Student> list = new ArrayList<>(Arrays.asList(new Student(1, "Julie"),
         new Student(2, "Robert"), new Student(3, "Adam")));

      // immutable version of list
      List<Student> c = Collections.unmodifiableList(list);
      System.out.println("Immutable list: "+ c);
   }
}
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 list: [[ 1, Julie ], [ 2, Robert ], [ 3, Adam ]]