Question

I dont understand the program below. I have mentioned the two errors I have encountered in the code. But I cannot understand the reason

import java.io.*;
class sdata
{
    float per;
    int m,tm=0,i,n;

    sdata(int n)throws Exception
    {
       DataInputStream dis2=new DataInputStream(System.in);
       for(i=1;i<=n;i++)
       {
        System.out.print("enter marks of subject"+i);
        int m=Integer.parseInt(dis2.readLine());
        tm=tm+m;
       }
       per=tm/n;
    }
}

class disdata extends sdata
{
    //below line gives an error "constructor sdata in class xyz.sdata cannot be applied to given types required:int found:no arguments"

    disdata() throws Exception{             
      System.out.println("TOTAL MARKS OF SUBJECTS:"+tm);
      System.out.println("PERCENTAGE OF STUDENT:"+per);
    }

}
class sresult
{
    public static void main(String args[])throws  Exception
    {
       DataInputStream dis=new DataInputStream(System.in);
       int n=Integer.parseInt(dis.readLine());

       disdata objj=new disdata();
       //the below line creates an error saying "cannot find symbol" 
       objj.sdata(n);
    }
}

Answer 1

sdata is super class of disdata and when you are creating a object of disdata with no argument and in disdata constructor you did not call sdata int constructor so by default it will try to find no argument sdata constructor, which is not available, so it gives error.

you can do thing call sdata int constructor from disdata constructor or crate a no argument constructor in sdata.

class sdata {
    float per;
    int m, tm = 0, i, n;
    sdata(int n) throws Exception {...}
    //No argument constructor
    sdata(){}
}