Java-扩展一个类的类，并具有扩展另一个类的组件的组件

Question

To clarify, this is a Stack and MinStack.

They use StackNode and MinStackNode respectively.

I'm trying to get MinStack to extend Stack and MinStackNode to extend StackNode. However, when I do so MinStack uses StackNode instead of MinStackNode.

This is because Stack uses StackNode and MinStack inherits this. I want MinStack to use MinStackNode.

Organization:

StackNode -> Stack

inherited by the classes below

MinStackNode -> MinStack

Any help would be appreciated. Thanks!

Code snippet for Stack:

public class Stack<E> implements StackInterface<E> {
    private StackNode<E> top;
    private int size;
    public Stack(E data){
        StackNode<E> node = new StackNode<E>(data);
        this.top = node;
    }
    public Stack(){
        this.top = null;
    }
}

MinStack:

public class MinStack<E extends Comparable<E>> extends Stack<E>{
    private MinStackNode<E> top;
    public MinStack(Stack<E> s){
        super(s);
    }
}

StackNode:

public class StackNode<E> {
    private E data;
    private StackNode<E> next;
    public StackNode(E data){
        this.data = data;
        this.next = null;
    }
}

MinStackNode:

public class MinStackNode<T> extends StackNode<T> {
    private T min;
    public MinStackNode(Comparator<T> comparator, T data) {
        super(data);
        this.min = minimum(this.getNext().getMin(), this.getData());
    }
}

For space I didn't include some methods such as MinStackNode's minimum. If needed I'll include them.

Answer 1

Well if MinStackNode inherits StackNode then you don't necessarily have to include the variable top in MinStackNode since a valid declaration already exists in StackNode . However you will need to cast the value to MinStackNode when you need to use any of the non-inherited properties/methods.

I think your problem here is that what you expect to be of type MinStackNode is actually of this type, but is being stored in a variable of a more general type and so must be cast.