Java - correct way to delegate methods

My program gets information from an external source (can be a file, a database, or anything else I might decide upon in the future).

I want to define an interface with all my data needs, and classes that implement it (e.g. a class to get the data from a file, another for DB, etc...).

I want the rest of my project to not care where the data comes from, and not need to create any object to get the data, for example to call "DataSource.getSomething();"

For that I need DataSource to contain a variable of the type of the interface and initialize it with one of the concrete implementations, and expose all of its methods (that come from the interface) as static methods.

So, lets say the interface name is K, and the concrete implementations are A,B,C.

The way I do it today is:

public class DataSource  {
    private static K myVar = new B();

    // For **every** method in K I do something like this:

    public static String getSomething() {
          return myVar.doSomething();
    }

    ...
}

This is very bad since I need to copy all the methods of the interface and make them static just so I can delegate it to myVar, and many other obvious reasons.

What is the correct way to do it? (maybe there is a design pattern for it?)

**Note - I insist on keeping it simple like "DataSource.getSomething();", I do not want anything like "DataSource.getInstance().getSomething();" **