A private variable or method may be used only by an instance of the class. : private « Modifiers « SCJP

1. SCJP
2. Modifiers
3. private

class Complex {
   private double real,  imaginary;

 public Complex(double r, double i) {
   real = r; imaginary = i;
 }
 public Complex add(Complex c) {
   return new Complex(real + c.real,
   imaginary + c.imaginary);
 }
}

public class MainClass{
   public static void main(String[] argv) {
     Complex c1 = new Complex(1, 2);
     Complex c2 = new Complex(3, 4);
     Complex c3 = c1.add(c2);
     //double d = c3.real; // Illegal!
   }
 }