Complex Number Operations In Java

To design a class Complex to represent operations on Complex numbers,ie. Addition, subtraction, modulus, conjugate, multiplication, division using objects of the same class.

import java.util.*;
class Complex
{ double r,i;
    public Complex()
    {r=0;
     i=0;
    }
    public Complex(double a,double b)
    {r=a;
     i=b;
    }
    public double mod()
    { return Math.sqrt(r*r+i*i);}
    public Complex conju()
    {Complex ob= new Complex();
     ob.r=this.r;
     ob.i=-this.i;
     return ob;
    }
    public Complex sum(Complex ob)
   { Complex xy= new Complex();
      xy.r=this.r+ob.r;
      xy.i=this.i+ob.i;
      return xy;
   }//end of sum()
    public Complex dif(Complex ob)
   { Complex xy1= new Complex();
      xy1.r=this.r-ob.r;
      xy1.i=this.i-ob.i;
      return xy1;
   }//end of dif()
    public Complex mul(Complex ob)
   { Complex p= new Complex();
      p.r=this.r*ob.r-ob.i*this.i;
      p.i=this.r*ob.i-ob.r*this.i;
      return p;
   }//end of mul()
    public Complex div(Complex ob)
   {  double den=Math.pow(ob.mod(),2);
      Complex d= new Complex();
      d.r=(this.r*ob.r+ob.i*this.i)/den;
      d.i=(this.i*ob.r-ob.i*this.r)/den;
      return d;
   }//end of div()
   public void display()
   { System.out.println(r+"i"+i);}//end of display()

public static void main()
  { int c;double u,v,w,z,d=0;
    Scanner sc=new Scanner(System.in);
    System.out.println("Press 1 for mod, 2 for conjugate,3 for sum,4 for difference,5 for multiplication, 6 for division");
    c=sc.nextInt();
    if(c==3)
     { System.out.println("enter the 1st complex number");
        w=sc.nextDouble();
        z=sc.nextDouble();
       System.out.println("enter the 2nd complex number");
        u=sc.nextDouble();
        v=sc.nextDouble();
        Complex ob1=new Complex(w,z);
        Complex ob2=new Complex(u,v);
        Complex ob3=new Complex();
        ob3=ob1.sum(ob2);
        System.out.println("sum is "+ob3.r+"+"+ob3.i+"i");
    }
    else if(c==1)
    {  System.out.println("enter the complex number");
        w=sc.nextDouble();
        z=sc.nextDouble();
        Complex ob1=new Complex(w,z);
        d=ob1.mod();
       System.out.println("the modulus is "+d);
   
    }
    else if(c==4)
    {System.out.println("enter the 1st complex number");
        w=sc.nextDouble();
        z=sc.nextDouble();
       System.out.println("enter the 2nd complex number");
        u=sc.nextDouble();
        v=sc.nextDouble();
        Complex ob1=new Complex(w,z);
        Complex ob2=new Complex(u,v);
        Complex ob3=new Complex();
        ob3=ob1.dif(ob2);
        System.out.println("difference is "+ob3.r+"i"+ob3.i);
    }else if(c==5)
    {System.out.println("enter the 1st complex number");
        w=sc.nextDouble();
        z=sc.nextDouble();
       System.out.println("enter the 2nd complex number");
        u=sc.nextDouble();
        v=sc.nextDouble();
        Complex ob1=new Complex(w,z);
        Complex ob2=new Complex(u,v);
        Complex ob3=new Complex();
        ob3=ob1.mul(ob2);
        System.out.println("multiplied number is "+ob3.r+"i"+ob3.i);
    }
    else if(c==6)
    {System.out.println("enter the 1st complex number");
        w=sc.nextDouble();
        z=sc.nextDouble();
       System.out.println("enter the 2nd complex number");
        u=sc.nextDouble();
        v=sc.nextDouble();
        Complex ob1=new Complex(w,z);
        Complex ob2=new Complex(u,v);
        Complex ob3=new Complex();
        ob3=ob1.dif(ob2);
        System.out.println("divided complex number is "+ob3.r+"i"+ob3.i);
    }
    else if(c==2)
    {  System.out.println("enter the complex number");
        w=sc.nextDouble();
        z=sc.nextDouble();
        Complex ob1=new Complex(w,z);
        Complex ob3=new Complex();
        ob3=ob1.conju();
       System.out.println("the conjugate is "+ob3.r+ob3.i+"i");
    }
    else
      System.out.println("Wrong Choice");
   }//end of class
}//end of class

OUTPUT---
Press 1 for mod, 2 for conjugate, 3 for sum,4 for difference,5 for multiplication, 6 for division
1
enter the complex number
2
5
the modulus is 5.385164807134504

Press 1 for mod, 2 for conjugate,3 for sum,4 for difference,5 for multiplication, 6 for division
2
enter the complex number
5
4

the conjugate is  5.0-4.0i

Press 1 for mod, 2 for conjugate,3 for sum,4 for difference,5 for multiplication, 6 for division
3
enter the 1st complex number
5
4
enter the 2nd complex number
3
2

sum is 8.0+6.0i

Press 1 for mod, 2 for conjugate,3 for sum,4 for difference,5 for multiplication, 6 for division
4
enter the 1st complex number
5
6
enter the 2nd complex number
2
3

difference is 3.0+3.0i

Press 1 for mod, 2 for conjugate,3 for sum,4 for difference,5 for multiplication, 6 for division
5
enter the 1st complex number
2
3
enter the 2nd complex number
4
9

multiplied number is  -19.0+6.0i

Press 1 for mod, 2 for conjugate,3 for sum,4 for difference,5 for multiplication, 6 for division
6
enter the 1st complex number
5
3
enter the 2nd complex number
7
2

divided complex number is  -2.0+1.0i