java constructor in super classes

Question

The following code is a testing program. Why i can't use A(int a), in this program?

public class A {
    int a;
    void meth(int b) {
        a+=b;
    }
    A(int a) {
        this.a=a;
    }
}

class B extends A {
    int a;
    void meh2(int b) {
        a+=b;
    }
}

why can't pass parameter to constructor? What the reasons? Netbeans error message:

constructor A in class tma1.A cannot be applied to given types; required: int found: no arguments reason: actual and formal argument lists differ in length

Answer 1

In the class B, you need constructor. If you mean that you can't call A from B, that's just because you're extending class A, so you need to use super, which refer to the superclass. For example B could be:

    class B extends A {
    B(int a) {
//You can put additional code here

// This calls the constructor of A
        super(a);

//You can put additional code here
    }
    int a;
    void meh2(int b) {
        a+=b;
    }
}

Otherwise you need to assign something to the variable a in class B, if you're not omitting something in code

Answer 2

Unless a class has a defined constructor, it automatically has a no-arg constructor that merely calls super() .

The complaint from your compiler seems to be: "your no-arg constructor [that you can't see] is calling up to a parent no-arg constructor that doesn't exist."

Class A doesn't have a no-arg constructor because there's another one defined (so java doesn't have to create one).