JAVA EE: Java : Collection Framework : Collections [UnModifiableList]

Tuesday 7 July 2015

Java : Collection Framework : Collections [UnModifiableList]

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Java - Collection Framework - Collections [UnModifiableList]

CollectionsExample.java

import java.util.ArrayList;

import java.util.Collections;
import java.util.List;

/*
 Example of:  

    unmodifiableList(List<? extends T> list) method

 Parameters:

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

 Returns:

    an unmodifiable view of the specified list.
 */

public class CollectionsExample
{

    public static void main(String[] args)
    {

        ArrayList<Integer> arrayList = new ArrayList<Integer>();

        arrayList.add(2000);
        arrayList.add(3000);
        arrayList.add(4000);
        arrayList.add(1000);

        System.out.println("arrayList : " + arrayList + "\n");

        /*
         * Returns an unmodifiable view of the specified list. 
         * 
         * This method allows modules to provide users with "read-only" access to internal
         * lists. 
         * 
         * Query operations on the returned list "read through" to the
         * specified list, and attempts to modify the returned list, whether
         * direct or via its iterator, result in an
         * UnsupportedOperationException.
         */

        List<Integer> unmodifiableList = Collections.unmodifiableList(arrayList);

        System.out.println("unmodifiableList : " + unmodifiableList+"\n");

        /* 
         * We cannot modify the unmodifiableList.
         */
        unmodifiableList.add(200);

    }

}

Output

arrayList : [2000, 3000, 4000, 1000]

unmodifiableList : [2000, 3000, 4000, 1000]

Exception in thread "main" java.lang.UnsupportedOperationException
    at java.util.Collections$UnmodifiableCollection.add(Collections.java:1055)
    at CollectionsExample.main(CollectionsExample.java:53)