Use of Java's Collections.singletonList()?

Question

What is the use of Collections.singletonList() in Java? I understand that it returns a list with one element. Why would I want to have a separate method to do that?

Answer 1

From the javadoc

@param  the sole object to be stored in the returned list.
@return an immutable list containing only the specified object.

example

import java.util.*;

public class HelloWorld {
    public static void main(String args[]) {
        // create an array of string objs
        String initList[] = { "One", "Two", "Four", "One",};

        // create one list
        List list = new ArrayList(Arrays.asList(initList));

        System.out.println("List value before: "+list);

        // create singleton list
        list = Collections.singletonList("OnlyOneElement");
        list.add("five"); //throws UnsupportedOperationException
        System.out.println("List value after: "+list);
    }
}

Use it when code expects a read-only list, but you only want to pass one element in it. singletonList is (thread-)safe and fast.