Java/Language Basics/Object Oriented Design

Class Hierachy

/*
 * Copyright (c) Ian F. Darwin, http://www.darwinsys.ru/, 1996-2002.
 * All rights reserved. Software written by Ian F. Darwin and others.
 * $Id: LICENSE,v 1.8 2004/02/09 03:33:38 ian Exp $
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS""
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * 
 * Java, the Duke mascot, and all variants of Sun"s Java "steaming coffee
 * cup" logo are trademarks of Sun Microsystems. Sun"s, and James Gosling"s,
 * pioneering role in inventing and promulgating (and standardizing) the Java 
 * language and environment is gratefully acknowledged.
 * 
 * The pioneering role of Dennis Ritchie and Bjarne Stroustrup, of AT&T, for
 * inventing predecessor languages C and C++ is also gratefully acknowledged.
 */
import java.util.*;
/** Part of a main program using Shape objects */
public class ClassShapeMain {
  Collection allShapes;  // created in a Constructor, not shown
  /** Iterate over all the Shapes, getting their areas */
  public double totalAreas() {
    Iterator it = allShapes.iterator();
    double total = 0.0;
    while (it.hasNext()) {
      Shape s = (Shape)it.next();
      total += s.ruputeArea();
    }
    return total;
  }
}
class Circle extends Shape {
  double radius;
  public double computeArea() {
    return Math.PI * radius * radius;
  }
}
class Rectangle extends Shape {
  double width, height;
  public double computeArea() {
    return width * height;
  }
}
abstract class Shape {
  protected int x, y;
  public abstract double computeArea();
}

Hierarchy 2

/*
 * Copyright (c) Ian F. Darwin, http://www.darwinsys.ru/, 1996-2002.
 * All rights reserved. Software written by Ian F. Darwin and others.
 * $Id: LICENSE,v 1.8 2004/02/09 03:33:38 ian Exp $
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS""
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * 
 * Java, the Duke mascot, and all variants of Sun"s Java "steaming coffee
 * cup" logo are trademarks of Sun Microsystems. Sun"s, and James Gosling"s,
 * pioneering role in inventing and promulgating (and standardizing) the Java 
 * language and environment is gratefully acknowledged.
 * 
 * The pioneering role of Dennis Ritchie and Bjarne Stroustrup, of AT&T, for
 * inventing predecessor languages C and C++ is also gratefully acknowledged.
 */
public class Customer extends Person {
  private int customerNumber;
  public Customer(String firstName, String lastName, int number) {
    super(firstName, lastName);
    setCustomerNumber(number);
  }
  public void setCustomerNumber(int n) {
    if (n < 1)
      throw new IllegalArgumentException("Invalid customer number " + n);
    customerNumber = n;
  }
}
class Person {
  String firstName;
  String lastName;
  Person(String firstName, String lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
  }
}
class Employee extends Person {
  private short deptCode;
  private int staffNumber;
  public Employee(String firstName, String lastName, short dept, int number) {
    super(firstName, lastName);
    setDeptCode(dept);
    setStaffID(number);
  }
  public void setDeptCode(short dept) {
    deptCode = dept;
  }
  public void setStaffID(int number) {
    if (number < 1)
      throw new IllegalArgumentException("Invalid staff number " +
        number);
    staffNumber = number;
  }
}

This class shows how we might control the objects

/*
 * Copyright (c) Ian F. Darwin, http://www.darwinsys.ru/, 1996-2002.
 * All rights reserved. Software written by Ian F. Darwin and others.
 * $Id: LICENSE,v 1.8 2004/02/09 03:33:38 ian Exp $
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS""
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * 
 * Java, the Duke mascot, and all variants of Sun"s Java "steaming coffee
 * cup" logo are trademarks of Sun Microsystems. Sun"s, and James Gosling"s,
 * pioneering role in inventing and promulgating (and standardizing) the Java 
 * language and environment is gratefully acknowledged.
 * 
 * The pioneering role of Dennis Ritchie and Bjarne Stroustrup, of AT&T, for
 * inventing predecessor languages C and C++ is also gratefully acknowledged.
 */
/**
 * BuildingManagement - control an energy-saving building.
 * This class shows how we might control the objects in an office
 * that can safely be powered off at nighttime to save energy - lots of
 * it, when applied to a large office!
 */
public class BuildingManagement {
  Asset things[] = new Asset[24];  
  int numItems = 0;
  /** goodNight is called from a timer Thread at 2200, or when we
   * get the "shutdown" command from the security guard.
   */
  public void goodNight() {
    for (int i=0; i<things.length; i++)
      if (things[i] instanceof PowerSwitchable)
        ((PowerSwitchable)things[i]).powerDown();
  }
  // goodMorning() would be the same, but call each one"s powerUp().
  /** Add a Asset to this building */
  public void add(Asset thing) {  
    System.out.println("Adding " + thing);
    things[numItems++] = thing;
  }
  /** The main program */
  public static void main(String[] av) {
    BuildingManagement b1 = new BuildingManagement();
    b1.add(new RoomLights(101));  // control lights in room 101
    b1.add(new EmergencyLight(101));  // and emerg. lights.
    // add the computer on desk#4 in room 101
    b1.add(new ComputerCPU(10104));
    // and its monitor
    b1.add(new ComputerMonitor(10104));
    // time passes, and the sun sets...
    b1.goodNight();
  }
}
abstract class BuildingLight extends BuildingAsset {
  // generic info on lighting: flourescent/incandescent, ...
  BuildingLight(int roomNumber) {
    super(roomNumber);
  }
}
abstract class ComputerAsset extends Asset {
  // generic computer component stuff here: location, owner, 
  // warranty expiration date :-), etc.
  int deskNumber;
  ComputerAsset(int deskNumber) {
    this.deskNumber = deskNumber;
  }
}
class ComputerCPU extends ComputerAsset {
  // information about CPU (P5, P6, ...), RAM, etc.
  ComputerCPU(int deskNumber) {
    super(deskNumber);
  }
}
/** Asset is the top level of every Asset */
abstract class Asset extends Object {
  // No fields or methods; it"s just the base of everything.
}
class EmergencyLight extends BuildingLight {  // NEVER SWITCH OFF
  EmergencyLight(int roomNumber) {
    super(roomNumber);
  }
}
/**
 * PowerSwitchable is an Interface that will be implemented by things
 * that can safely be turned off at night. Could use X10(tm) or BlueTooth
 * or 802.11 or any similar network technology to turn things on or off.
 *
 * @author  Ian F. Darwin
 */
interface PowerSwitchable {
  /** The technique for turning this unit off */
  public void powerDown();
  /** The technique for turning this unit on */
  public void powerUp();
}
class RoomLights extends BuildingLight implements PowerSwitchable {
  RoomLights(int roomNumber) {
    super(roomNumber);
  }
  public void powerDown() {
    System.out.println("Dousing lights in room " + room);
  }
  public void powerUp() {
    System.out.println("Lighting lights in room " + room);
  }
}
/** The top level of everything that is permanently part of the building */
abstract class BuildingAsset extends Asset {
  protected int room;
  public BuildingAsset(int room) {
    this.room = room;
  }
}
class ComputerMonitor extends ComputerAsset implements PowerSwitchable {
  ComputerMonitor(int roomNumber) {
    super(roomNumber);
  }
  public void powerDown() {
    System.out.println("Dousing monitor at desk " + deskNumber);
    // send the code to the Monitor"s X10 box to shut it off
  }
  public void powerUp() {
    System.out.println("Warming up monitor at desk " + deskNumber);
    // send the code to the Monitor"s X10 box to turn it on
  }
}