The document contains code for a Student class in Java and Scala. The Java class contains a constructor that increments a static variable b each time an object is created. It also contains methods to print the values of instance variable a and static variable b. The Scala code separates the class and singleton object, with the singleton containing the static variable b and a method that would cause an error by modifying the instance variable.

1. package features.companions.java;
public class Student {
int a;
static int b;
public Student() {
//Constructor incrementing static var b
Student.b++;
}
public void showData() {
System.out.println("Value of a = "+a);
System.out.println("Value of b = "+b);
}
public static void increment() {
a++; // confusing error
}
}
class Demo{
public static void main(String args[]) {
Student s1 = new Student();
s1.showData();
Student s2 = new Student();
s2.showData();
Student.b++;
s1.showData();
}
}
package features.companions.scala
class Student {
var a = 0
//Constructor incrementing
// static variable b
Student.b += 1;
def showData() {
println("Value of a = "+a);
println("Value of b = "+Student.b);
}
}
object Student {
var b = 0
def increment { a += 1 } // obvious error
}
21
In Scala, they are separated:
- a class for the parts you can instantiate into individual objects
- a singleton or “companion object” for the parts that there only needs to be one of