Question

In what way does the access specifier of the base class have access control over the derived class? Show with the help of an example. 

Answer 1

1. Assume Science is the base class (super class) and Physics is its derived class.
2. If class Science is public or protected, the subclass Physics can access all base class data elements.
3. If class Science is declared private or there is no access specifier, subclass Physics will not have access to the base class's data members.
4. Example: 

   class A {
       public int x;
       protected int y;
       private int z;
   
       public A() {
           x = 10;
           y = 20;
           z = 30;
       }
   
       public int sum() {
           return x + y + z;
       }
   }
   
   class B extends A {
       int total;
   
       void computeTotal() {
           /*
            * Public method sum() of base class
            * is accessible here
            */
           total = sum();
       }
   
       void display() {
           /*
            * x is accessible as it is public
            */
           System.out.println("x = " + x);
   
           /*
            * y is accessible as it is protected
            */
           System.out.println("y = " + y);
   
           /*
            * This will give ERROR!!!
            * z is not accessible as it is private
            */
           System.out.println("z = " + z);
       }
   }