The Collection Program Singleton used to return an immutable list containing only the specified object using SingletonList(T o) method

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The singletonList(T) method is used to return an immutable list containing only the specified object.

Example Program

import java.util.*;

public class List111 {
	public static void displayList(List<String> l) {
		Iterator<String> i = l.iterator();
		while (i.hasNext())
			System.out.print("\t" + i.next());
		System.out.println();
	}

	public static void main(String[] args) {
		String init[] = { "One", "Two", "Three", "One", "Two", "Three" };
		List<String> list = new ArrayList<String>(Arrays.asList(init));
		System.out.println("Size of 'List' :" + list.size());
		System.out.println("Before Singleton List apply");
		System.out.println("Contents of the list 'list':");
		displayList(list);
		System.out.println();
		list = Collections.singletonList("four");
		System.out.println("After Sigleton List applied ");
		System.out.println("Contents of the list 'list':");
		displayList(list);
		System.out.println("Size of 'List': " + list.size());
	}
}

Output:

Size of ‘List’ :6

Before Singleton List apply

Contents of the list ‘list’:

One Two Three  One Two Three

After Sigleton List applied

Contents of the list ‘list’:

four

Size of ‘List’: 1

Explanation:

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

The singletonList(T) method is used to return an immutable list containing only the specified object.

Parameters:

o – the sole object to be stored in the returned set.

Returns:

An immutable set containing only the specified object. The returned list is serializable.

Since:

1.3