了解Java中的继承

Question

I was practising some of the inheritance concept which i have learned from my book although i haven't completely studied inheritance yet but i thought to just write a simple program based on inheritance here is it

public class InheritanceInJava
{
    public static void main(String args[])
    {
       SupperClass_A supperObj_A = new SupperClass_A(20,30,10);
       SubClass_A subObj_A = new SubClass_A(10,20,30);
       System.out.println(subObj_A.Add());
       System.out.println(subObj_A.Multiply());
    }
}

class SupperClass_A
{
   int num1 ; int num2 ; int num3 ;
   SupperClass_A(int a, int b, int c)
   {
      num1 = a ; num2 = b ; num3 = c;
   }
  public int Multiply()
  {
     return num1 * num2 * num3;
  }
}

class SubClass_A extends SupperClass_A
{
  SubClass_A(int a, int b, int c)
  {
      num1 = a ; num2 = b ; num3 = c;
  }
  public int Add()
  {
      return num1 + num2 + num3;
  }
}

but it shows one error which is :

constructor SupperClass_A in class SupperClass_A cannot be applied to given types; { ^ required: int,int,int found: no arguments reason: actual and formal argument lists differ in length

Can anyone help me understand why this program is not working and whats the cause for this error ?

Answer 1

The issue is that your SubClass_A constructor attempts to implicitly call a parameter-less constructor of SupperClass_A , which doesn't exist. A parameter-less constructor is generated automatically by the compiler only for classes that don't have any explicitly defined constructors.

You can fix it by calling the super class constructor explicitly :

class SubClass_A extends SupperClass_A
{
  SubClass_A(int a, int b, int c)
  {
      super(a,b,c);
  }
  public int Add()
  {
      return num1 + num2 + num3;
  }
}