understand concept of class object and method

/*

Aim : Write a program to understand concept of class object and method.
*/
import java.lang.*;
import java.io.*;

class rectangle
{
int a;
int calca(int l,int b)
{
a=l*b;
return(a);
}
int calcperi(int l,int b)
{
a=(2*l)+(2*b);
return(a);
}
}

class square
{
int a;
int calca(int l)
{
a=l*l;
return(a);
}
int calcperi(int l)
{
a=(4*l);
return(a);
}
}

class circle
{
double a;
double calca(int r)
{
a=r*r*3.14;
return(a);
}
double calcperi(int r)
{
a=(2*3.14*r);
return(a);
}
}

class pr_1
{
public static void main(String args[])
{
int i=10,j=20;
rectangle obj1=new rectangle();
System.out.println("\n*****Recrangle having Length = "+i+" and Breath = "+j+"*****");
System.out.println("\t\t1)Area = "+obj1.calca(i,j));
System.out.println("\t\t2)Perimeter =  "+obj1.calcperi(i,j));

System.out.println("\n");
i=40;
square obj2=new square();
System.out.println("\n********Square with having Length & breath =  "+i+"  ******");
System.out.println("\t\t1)Area = "+obj2.calca(i));
System.out.println("\t\t2)Perimeter =  "+obj2.calcperi(i));

System.out.println("\n");
i=25;
circle obj3=new circle();
System.out.println("\n*****Circle with radius : "+i+"  *****");
System.out.println("\t\t1)Area = "+obj3.calca(i));
System.out.println("\t\t2)Perimeter =  "+obj3.calcperi(i));
}
}

/* OUTPUT
prashant@prashant-OptiPlex-755:~$ javac pr_1.java
prashant@prashant-OptiPlex-755:~$ java pr_1

*****Recrangle having Length = 10 and Breath = 20*****
1)Area = 200
2)Perimeter =  60



********Square with having Length & breath =  40  ******
1)Area = 1600
2)Perimeter =  160



*****Circle with radius : 25  *****
1)Area = 1962.5
2)Perimeter =  157.0
prashant@prashant-OptiPlex-755:~$

*/