Understanding Inheritance in java

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 ?

since you declared a parameterized constructor in your SuperClass_A you have to call it from the Constructor in your SubClass. — Timothy Truckle
– Timothy Truckle, Commented Oct 27, 2016 at 12:51
(Correcting SupperClass to SuperClass) -- A SuperClass_A constructor has to be called when you make a SubClass_A instance, because every SubClass_A instance is also a SuperClass_A instance. Your SubClass_A does not specify what SuperClass_A constructor should be called (using super(a,b,c)), so the compiler assumes you want to call the no-arguments constructor. But there isn't a no-arguments constructor, so the compile fails. — khelwood
– khelwood, Commented Oct 27, 2016 at 12:51

Eran · Accepted Answer · 2016-10-27 12:50:49Z

4

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;
  }
}

answered Oct 27, 2016 at 12:50

Eran

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