Java Utility Library

Java Collections - unmodifiableList() Method

The java.util.Collections.unmodifiableList() method returns an unmodifiable view of the specified list.

Syntax

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

Here, T is the type of element in the list.

Parameters

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

Return Value

Returns an unmodifiable view of the specified list.

Exception

NA.

Example:

In the example below, the java.util.Collections.unmodifiableList() method returns an unmodifiable view of the given list.

import java.util.*;

public class MyClass {
  public static void main(String[] args) {
    //creating a list object
    List<Integer> MyList = new ArrayList<Integer>();

    //populating the list
    MyList.add(10);
    MyList.add(20);
    MyList.add(30);
    MyList.add(40);

    //printing the list
    System.out.println("MyList contains: " + MyList); 

    //creating an unmodifiable view of the list
    List NewList = Collections.unmodifiableList(MyList);

    //printing the unmodifiable list
    System.out.println("NewList contains: " + NewList); 

    //trying to modify the NewList
    NewList.add(50);     
  }
}

The output of the above code will be:

MyList contains: [10, 20, 30, 40]
NewList contains: [10, 20, 30, 40]

Exception in thread "main" java.lang.UnsupportedOperationException
    at java.base/java.util.Collections$UnmodifiableCollection.add(Collections.java:1060)
    at MyClass.main(MyClass.java:24)

❮ Java.util - Collections