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Showing content from https://www.tutorialspoint.com/java/util/collections_unmodifiablelist.htm below:

Java Collections unmodifiableList() Method

Java Collections unmodifiableList() Method 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

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 ]]

java_util_collections.htm

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