Java : Collection Framework : Collections (Singleton)

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CollectionsExample.java

import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Set;

/*
 Method: 

 public static <T> Set<T> singleton(T o)

 Parameters:
 o - the sole object to be stored in the returned set.

 Returns:

 an immutable set containing only the specified object.

 ---------------------------------------------------------------

 Method: 

 public static <T> List<T> singletonList(T o)

 Parameters:

 o - the sole object to be stored in the returned list.

 Returns:

 an immutable list containing only the specified object.

 ----------------------------------------------------------------

 Method: 

 public static <K,V> Map<K,V> singletonMap(K key,
 V value)

 Parameters:

 key - the sole key to be stored in the returned map.
 value - the value to which the returned map maps key.

 Returns:

 an immutable map containing only the specified key-value mapping.

 */

public class CollectionsExample
{

    public static void main(String[] args)
    {

        /*
         * Returns an immutable set containing only the specified object.
         */
        Set<String> singleTonSet = Collections.singleton("Dave");

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

        /*
         * We cannot add or modify the immutable set.
         */

        // singleTonSet.add("Ram");

        /*
         * Returns an immutable list containing only the specified object.
         */
        List<String> singleTonList = Collections.singletonList("Julia");

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

        /*
         * Returns an immutable list containing only the specified object.
         */
        Map<String, String> singletonMap = Collections.singletonMap("IN",
                "India");

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

    }

}

Output

singleTonSet : [Dave]

singleTonList : [Julia]

singleTonMap : {IN=India}

To Download CollectionsDemo-singletonApp Project Click the below link
https://sites.google.com/site/javaee4321/java-collections/CollectionsDemo-singletonApp.zip?attredirects=0&d=1

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