Inheritance Issue - constructor

Question

Okay, I hope you guys can help me out of this. I currently have an interface designed, with a class inheriting its information. Here is the sample code for reference:
ArrayStack
public class ArrayStack
    implements AnotherInterface
    public ArrayStack(int stacksize)
        stack = new String[stacksize];
    public boolean isFull()
        return top == stack.length;
}Now the problem arises when I want to create a new class which inherits the ArrayStack. Here is a sample code of what I have wrote up:
public class checkSize extends ArrayStack
    public checkSize()
}I'm just trying to get my head around inheritance, but this code keeps giving me the error "cannot find symbol - constructor". Can anyone point me to the right direction or tell me what I can do? Any help would be greatly appreciated!

Answer 1

Connex007 wrote:
Melanie_Green wrote:
So as suggested you can either call another constructor or you can create a default constructor in your superclass,Now that's where I'm getting confused on - what other constructor can I call?There is only one other constructor to call in the super class.
Remember that the first line of every constructor is either an explicit or implicit call to another constructor. If you do not explicitly call another constructor then super() is inserted during compile time, and the default constructor that has no parameters of the superclass is called.
Furthermore any class that does not explicitly extend another class, extends Object. So as I stated previously if the first line of the any constructor in this class is not a call to another constructor, then the compiler will insert super() which will invoke the default constructor of Object.
Now in your scenario you are using inheritance, you have a subclass extending a superclass. Note that you have not defined a default constructor in the super class, which for example is defined in Object. So inside your subclass, if you do not call another constructor on the first line, then again the compiler will insert a call to super(). The call to super() from the subclass is dependent on the superclass having defined a default no parameter constructor. However in your case the superclass does not have such a constructor defined. Therefore you are still required to instantiate every class in the inheritance tree, either explicitly or implicitly.
If you are still weary at this point, think of it this way. If A extends B extends C. When an object of type A is instantiated, a constructor of A then B then C is called so that C is instantiated first, then B, then A. This is reflective of instantiated in a top down method so that each subclass is instantiated correctly. Since A extends B, and B can potentially be instantiated in one or more ways, you still need to define how both A and B are instantiated.
So relating this back to your problem, what are all the possible ways in which your superclass can be instantiated? We can eliminate the default constructor and assume that we must specify on the first line of the constructor contained in the subclass that a call to a constructor in the subclass or superclass occurs. If we invoke a constructor in the same class, in the subclass, then either this constructor calls a constructor in the super class, or it calls a constructor that in turn will tinkle its way up to calling a constructor in the superclass.
Mel