Multiple child class vs Single child class - Java Inheritance

I have a question that extending a Parent class to multiple child classes is a good practice or maintaining a single child is a good practice? Does this affects the scalability? All the classes will be executed at the same time. So I have this question.

for example I have used only 4 classes. In real time It will be like 83 classes will be using the same method and gets executed at once.

public interface A
{
  methodA();
}

public class B implements A
{
  methodA()
  {
    .....
  }
}

public class C
{
  B b = new B();
  b.methodA();
}

public class D
{
  B b = new B();
  b.methodA();
}

Or

public interface A
{
  methodA();
}

public class B implements A
{
  methodA()
  {
    .....
  }
}

public class C extends B
{
  super.methodA();
}

public class D extends B
{
  super.methodA();
}

Or

public interface A
{
  methodA();
}

public class B implements A
{
  methodA()
  {
    .....
  }
}

public class C extends B
{
  super.methodA();
}

public class D extends C
{
  super.methodA();
}

Go through the SOLID principle. Its a design principles encourage us to create more maintainable, understandable, and flexible software. Consequently, as our applications grow in size, we can reduce their complexity and save ourselves a lot of headaches further down the road!

You could define the code for methodA if you use the private or default access modifier.
Lesson: Interfaces and Inheritance (The Java™ Tutorials > Learning the Java Language).

interface A {
    private String method() {
        return "stack overflow";
    }
}

class B implements A {
    String string = A.super.method();
}