How to expose methods of a private class?

I am trying to write a library. Let's call it myLib.

public class MyLib {
    public SomeClass someClass =  SomeClass.INSTANCE();

    private static MyLib _instance = null;
    
    public static MyLib INSTANCE()
    {
        if (_instance == null)
            _instance = new MyLib();

        return _instance;
    }
}

SomeClass looks like this:

class SomeClass {
    
    private static SomeClass _instance = null;
    
    public static SomeClass INSTANCE()
    {
        if (_instance == null)
            _instance = new SomeClass();

        return _instance;
    }
    
    public void print(String message){
        System.out.println(message);
    }
}

I'd like users to be able to write: MyLib.INSTANCE().someClass.print("Hello World!");

However, in its current form, print is inaccessible. I do not want the user to be able to simply bypass MyLib.INSTANCE() and write SomeClass.INSTANCE().print("Hello World"); because some initialisation is done.

How can I solve this?

To make SomeClass.print accessible, SomeClass itself needs to be accessible.

To make SomeClass.INSTANCE not accessible, remove the public modifier. Since you are only accessing from the same package, use the "default" access which has no explicit access modifier:

// public access
public class SomeClass {
    // package-only access
    static SomeClass INSTANCE() { }
    // public access
    public void print(String message) { }
}

You have to keep SomeClass as an inner private class to prevent its direct accessibility and usage in MyLib class.

public static class MyLib {
    public SomeClass someClass =  SomeClass.INSTANCE();

    private static MyLib _instance = null;
    
    public static MyLib INSTANCE()
    {
        if (_instance == null)
            _instance = new MyLib();

        return _instance;
    }
    
    private static class SomeClass {
	    
	    private static SomeClass _instance = null;
	    
	    public static SomeClass INSTANCE()
	    {
	        if (_instance == null)
	            _instance = new SomeClass();

	        return _instance;
	    }
	    
	    public void print(String message){
	        System.out.println(message);
	    }
	}
}

Edit:

The solution to do without nested class using protected modifier

MyLib class in com.lib package

package com.lib;
public class MyLib {
    public SomeClass someClass =  SomeClass.INSTANCE();

    private static MyLib _instance = null;
    
    public static MyLib INSTANCE()
    {
        if (_instance == null)
            _instance = new MyLib();

        return _instance;
    }
}

SomeClass class in com.lib package

package com.lib;
public class SomeClass {
	    
	 private static SomeClass _instance = null;
	    
	    protected static SomeClass INSTANCE()
	    {
	        if (_instance == null)
	            _instance = new SomeClass();

	        return _instance;
	    }
	    
	    public void print(String message){
	        System.out.println(message);
	    }
	}

Accessing it in your main project (i.e. different package)

package com.project;
public class MainClass {

	public static void main(String[] args) {
       MyLib.INSTANCE().someClass.print("Hello World!");
    }
}