Question

class Super {
   protected int a;
   protected Super(int a) { this.a = a; }
}

class Sub extends Super {
    public Sub(int a) { super(a); }
    public Sub() { this.a = 5; }
}




  public Sub() { this.a = 5; }  

this.a=5 doesn’t work. Why is this so? Protected and public members should be inherited.

Answer 1

The problem isn’t that you access the variable, but that you don’t call the base constructor:

class Super {
   protected int a;
   protected Super(int a) { this.a = a; }
}

class Sub extends Super {
    public Sub(int a) { super(a); }
    public Sub() { 
       super(0);  // <-- call base constructor
       this.a = 5; 
    }
}

This happens because you didn’t define a default constructor for Super, so derived classes don’t know which constructor to call if you’re not specifying one.