此 java 代码中引用变量的使用

Question

Why is the reference variable ‚Input inside' necessary? How does the ‚Input inside' work here?

What does the code: The code adds 5 to the x-value (in this case 4) and uses the square of the new value. So (4+5)^2.

Thank you.

Code:

abstract class Input {

    protected Input inside;

    public Input() {
    }

    public Input(Input inside) {
        this.inside = inside;
    }


    public int calculate(int value) {
        if(inside == null) {
            return value;
        }
        return inside.calculate(value);
    }

    public static void main(String[] args) {
        Input chaincalculate = new Square(new AddFive());
        int x;
        x = 4;
        System.out.println("The value is: " + (int) chaincalculate.calculate(x));
    }
}
     
class AddFive extends Input {

    public AddFive() {
    }

    public AddFive(Input inside) {
        super(inside);
    }

    public int calculate(int value) {
        value = super.calculate(value);
        return value+5;
    }
}

class Square extends Input {

    public Square() {
    }

    public Square(Input inside) {
        super(inside);
    }

    public int calculate(int value) {
        value = super.calculate(value);
        return value * value;
        }
    }
}

Answer 1

All the classes extending the abstract class Input , have their own calculate methods , and since, these classes, would want to use the abstract class Calculate method , the reference variable input inside is necessary to invoke/reference the calculate method residing in Input abstract class , to support the method chaining implemented in the code