Introduction
Class Definition
Data Fields
Methods
Constructors
Instantiation
  Demo 1
  Demo 2
Static Members
  Demo 3
Value&Reference
  Demo 4
Overloading
   Demo 5
Wrappers 
  Demo 6
Autobox/Unbox
   Demo 7
Arrays
  Demo 8
Exceptions
Exercises

For the physicist one of the obvious examples that comes to mind when considering a good subject for object representation is a particle. A particle is a self contained physical object with well defined attributes and behavior.

We might provide a class for fundamental particles such as an electron, quarks and photons, or composite particles such as protons, atoms, and molecules.

Below we show a class that holds the essential properties of a stable particle. We will show in later chapters how this class could be extended by sub-classes to include additional properties such as lepton number, quark content, half-life for unstable particles, etc.

We also do not include kinematic information, such as the particle's momentum or kinetic energy. That depends on the frame of reference and this class only deals with the internal state properties of a particle at rest. We will show later how an interface can add such kinematical values.

// A base class for particles.

public class Particle
{

  // Instance variables
  String name;  // e.g. electron, proton, etc.

  double mass;  // rest mass in MeV/c^2

  int charge;   // integer charge only (ignore quarks)
  int  spin;    // multiple of 1/2

  // Constructor
  public Particle(String name, double mass,
                  int charge, int spin)
  {
    this.name = name;
    this.mass = mass;
    this.charge = charge;
    this.spin = spin;
  }

  public String getName()
  {
    return name;
  }
  public double getMass()
  {
    return mass;
  }

  public int getCharge()
  {
    return charge;
  }
  public int getSpin()
  {
    return spin;
  }
}

Furthermore, special classes called Java Beans require the use of such names so that bean tools can automatically recognize the function of a particular method.

We can then use the above class as follows:

  Particle [] particles = new Particle[4];

  particle[0] = new Particle("electron", 0.511, -1, 1);
  particle[1] = new Particle("positron", 0.511,  1, 1);
  particle[2] = new Particle("proton",   938.0,  1, 1);
  particle[3] = new Particle("neutron",  940.0,  0, 1);

to define an array of four different types of particles.

Latest update: Dec.15.2003

           Tech
OOP in Tech Apps
Complex Number
Histogram Class
  Demo
More Wrappers

           Physics
OOP in Physics
Particle Class
Root Finding
  Demo 1
Newton Methods
  Demo 2
Exercises