What is a Subclass

Subclass is to Class as Java is to Programming Language.

A subclass is a class that extends another class.

public class BaseClass{
    public String getFoo(){
        return "foo";
    }
}

public class SubClass extends BaseClass{
}

Then...

System.out.println(new SubClass().getFoo());

Will print:

foo

This works because a subclass inherits the functionality of the class it extends.

A subclass is something that extends the functionality of your existing class. I.e.

Superclass - describes the catagory of objects:

public abstract class Fruit {

    public abstract Color color;

}

Subclass1 - describes attributes of the individual Fruit objects:

public class Apple extends Fruit {

    Color color = red;

}

Subclass2 - describes attributes of the individual Fruit objects:

public class Banana extends Fruit {

    Color color = yellow;

}

The 'abstract' keyword in the superclass means that the class will only define the mandatory information that each subclass must have i.e. A piece of fruit must have a color so it is defines in the super class and all subclasses must 'inherit' that attribute and define the value that describes the specific object.

Does that make sense?