****************************
Code examples for interfaces:

    * Class1.java implements Interface1.java
    * Abstract Class2.java implements Interface1.java and Interface2.java
    * Class3.java extends abstract class Class2.java
    * Interface3.java extends Interface1.java and Interface2.java
***************************
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Class1.java 
~~~~~~~~~~~~~~~~~~~~~~~~~~~

// This class is not abstract, so it must provide 
// implementations of method1 and method2.

public class Class1 extends SomeClass
                    implements Interface1 {
  public ReturnType1 method1(ArgType1 arg) {
    someCodeHere();
    ...
  }
                      
  public ReturnType2 method2(ArgType2 arg) {
        someCodeHere();
    ...
  }

  ...
}
>>>>>>>>>>>>>>>>>>>>>>>>>>
~~~~~~~~~~~~~~~~~~~~~~~~~~
Interface1.java
~~~~~~~~~~~~~~~~~~~~~~~~~~
public interface Interface1 {
   ReturnType1 method1(ArgType1 arg);
  ReturnType2 method2(ArgType2 arg);
}
>>>>>>>>>>>>>>>>>>>>>>>>>>
~~~~~~~~~~~~~~~~~~~~~~~~~~
Abstract Class2.java implements Interface1.java and Interface2.java
~~~~~~~~~~~~~~~~~~~~~~~~~~
Class2.java 
~~~~~~~~~~~~~~~~~~~~~~~~~~

// This class is abstract, so does not have to provide
// implementations of the methods of Interface 1 and 2.

public abstract class Class2 extends SomeOtherClass
                             implements Interface1,
                                        Interface2 {
  ...
}
>>>>>>>>>>>>>>>>>>>>>>>>>
~~~~~~~~~~~~~~~~~~~~~~~~~
Interface2.java
~~~~~~~~~~~~~~~~~~~~~~~~~

public interface Interface2 {
  ReturnType3 method3(ArgType3 arg);
}
~~~~~~~~~~~~~~~~~~~~~~~~~
# Class3.java extends abstract class Class2.java 
~~~~~~~~~~~~~~~~~~~~~~~~~
Class3.java
>>>>>>>>>>>>>>>>>>>>>>>>>

// This class is not abstract, so it must provide
// implementations of method1, method2, and method3.

public class Class3 extends Class2 {
  public ReturnType1 method1(ArgType1 arg) {
    someCodeHere();
    ...
  }
                      
  public ReturnType2 method2(ArgType2 arg) {
       someCodeHere();
    ...
  }

  public ReturnType3 method3(ArgType3 arg) {
     someCodeHere();
    ...
  }

  ...
}
>>>>>>>>>>>>>>>>>>>>>>>
# Interface3.java extends Interface1.java and Interface2.java
>>>>>>>>>>>>>>>>>>>>>>>
~~~~~~~~~~~~~~~~~~~~~~
Interface3.java 
~~~~~~~~~~~~~~~~~~~~~~

// This interface has three methods (by inheritance) and 
// two constants.

public interface Interface3 extends Interface1,
                                    Interface2 {
  int MIN_VALUE = 0;
  int MAX_VALUE = 1000;
}
<<<<<<<<<<<<<<<<<<<<<

************************
Ship.java A Ship class illustrating object-oriented programming concepts. Incorporates Javadoc comments. See ShipTest.java for a test. 
************************
/** Ship example to demonstrate OOP in Java.
 *
 *  @author 
 *          Larry Brown
 *  @version 2.0
 */

public class Ship {
  // Instance variables

  private double x=0.0, y=0.0, speed=1.0, direction=0.0;
  private String name;

  // Constructors

  /** Build a ship with specified parameters. */

  public Ship(double x, double y, double speed,
              double direction, String name) {
    setX(x);
    setY(y);
    setSpeed(speed);
    setDirection(direction);
    setName(name);
  }

  /** Build a ship with default values
   *  (x=0, y=0, speed=1.0, direction=0.0).
   */

  public Ship(String name) {
    setName(name);
  }

  /** Move ship one step at current speed/direction. */

  public void move() {
    moveInternal(1);
  }

  /** Move N steps. */

  public void move(int steps) {
    moveInternal(steps);
  }

  private void moveInternal(int steps) {
    double angle = degreesToRadians(direction);
    x = x + (double)steps * speed * Math.cos(angle);
    y = y + (double)steps * speed * Math.sin(angle);
  }

  private double degreesToRadians(double degrees) {
    return(degrees * Math.PI / 180.0);
  }

  /** Report location to standard output. */

  public void printLocation() {
    System.out.println(getName() + " is at (" + getX() +
                       "," + getY() + ").");
  }

  /** Get current X location. */

  public double getX() {
    return(x);
  }

  /** Set current X location. */

  public void setX(double x) {
    this.x = x;
  }

  /** Get current Y location. */

  public double getY() {
    return(y);
  }

  /** Set current Y location. */

  public void setY(double y) {
    this.y = y;
  }

  /** Get current speed. */

  public double getSpeed() {
    return(speed);
  }

  /** Set current speed. */

  public void setSpeed(double speed) {
    this.speed = speed;
  }

  /** Get current heading (0=East, 90=North, 180=West,
   *  270=South).  I.e., uses standard math angles, not
   *  nautical system where 0=North, 90=East, etc.
   */

  public double getDirection() {
    return(direction);
  }

  /** Set current direction (0=East, 90=North, 180=West,
   *  270=South). I.e., uses standard math angles,not
   *  nautical system where 0=North,90=East, etc.
   */

  public void setDirection(double direction) {
    this.direction = direction;
  }

  /** Get Ship's name. Can't be modified by user. */

  public String getName() {
    return(name);
  }

  private void setName(String name) {
    this.name = name;
  }
}
*********************
ShipTest.java 
*********************
public class ShipTest {
 public static void main(String[] args) {
    Ship s1 = new Ship("Ship1"); 
    Ship s2 = new Ship(0.0, 0.0, 2.0, 135.0, "Ship2");
    s1.move();
    s2.move(3);
    s1.printLocation();
    s2.printLocation();
  }
}

Test1.java Accesses instance variables in a Ship object. 
********************************************************

// Create a class with five instance variables (fields):
// x, y, speed, direction, and name. Note that Ship1 is 
// not declared "public", so it can be in the same file as
// Test1. A Java file can only contain one "public" class
// definition.

class Ship1 {
  public double x, y, speed, direction;
  public String name;
}

// The "driver" class containing "main".

public class Test1 {
  public static void main(String[] args) {
    Ship1 s1 = new Ship1();
    s1.x = 0.0;
    s1.y = 0.0;
    s1.speed = 1.0;
    s1.direction = 0.0;   // East
    s1.name = "Ship1";
    Ship1 s2 = new Ship1();
    s2.x = 0.0;
    s2.y = 0.0;
    s2.speed = 2.0;
    s2.direction = 135.0; // Northwest
    s2.name = "Ship2";
    s1.x = s1.x + s1.speed
           * Math.cos(s1.direction * Math.PI / 180.0);
    s1.y = s1.y + s1.speed
           * Math.sin(s1.direction * Math.PI / 180.0);
    s2.x = s2.x + s2.speed
           * Math.cos(s2.direction * Math.PI / 180.0);
    s2.y = s2.y + s2.speed
           * Math.sin(s2.direction * Math.PI / 180.0);
    System.out.println(s1.name + " is at ("
                       + s1.x + "," + s1.y + ").");
    System.out.println(s2.name + " is at ("
                       + s2.x + "," + s2.y + ").");
  }
}
**********************

******************
ShowArgs.java Application that reports all command-line arguments.
******************
 */

public class ShowArgs {
  public static void main(String[] args) {
    for(int i=0; i

DropBall.java Uses a while loop to determine how long it takes a ball to fall from the top of the Washington Monument to the ground
************************************************************
/** Simulating dropping a ball from the top of the Washington
 *  Monument. The program outputs the height of the ball each
 *  second until the ball hits the ground.
 *
 *****************************************

public class DropBall {
  public static void main(String[] args) {
    int time = 0;
    double start = 550.0, drop = 0.0;
    double height = start;
    while (height > 0) {
      System.out.println("After " + time + 
                   (time==1 ? " second, " : " seconds,") + 
                   "the ball is at " + height + " feet.");
      time++;                   
      drop = freeFall(time);
      height = start - drop;
    }
    System.out.println("Before " + time + " seconds could " +
                       "expire, the ball hit the ground!");
  }
  
  /** Calculate the distance in feet for an object in 
   *  free fall. 
   */

  public static double freeFall (float time) {
    // Gravitational constant is 32 feet per second squared
    return(16.0 * time * time); // 1/2 gt^2
  }
}
@@@@@@@@@@@@@@@@@@@@

import java.text.*;

/** Formatting real numbers with DecimalFormat.
 *
 *  Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

public class NumFormat {
  public static void main (String[] args) {
    DecimalFormat science = new DecimalFormat("0.000E0");
    DecimalFormat plain = new DecimalFormat("0.0000");

    for(double d=100.0; d<140.0; d*=1.10) {
      System.out.println("Scientific: " + science.format(d) +
                         " and Plain: " + plain.format(d));
    }
  }
}

/** Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

import java.awt.Point;

public class ModificationTest extends ReferenceTest {
  public static void main(String[] args) {
    Point p1 = new Point(1, 2); // Assign Point to p1
    Point p2 = p1; // p2 is new reference to *same* Point
    print("p1", p1); // (1, 2)
    print("p2", p2); // (1, 2)
    munge(p2); // Changes fields of the *single* Point
    print("p1", p1); // (5, 10)
    print("p2", p2); // (5, 10)
  }

  public static void munge(Point p) {
    p.x = 5;
    p.y = 10;
  }
}


/** Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

import java.awt.Point;

public class ReferenceTest {
  public static void main(String[] args) {
    Point p1 = new Point(1, 2); // Assign Point to p1
    Point p2 = p1; // p2 is new reference to *same* Point
    print("p1", p1); // (1, 2)
    print("p2", p2); // (1, 2)
    triple(p2); // Doesn?t change p2
    print("p2", p2); // (1, 2)
    p2 = triple(p2); // Have p2 point to *new* Point
    print("p2", p2); // (3, 6)
    print("p1", p1); // p1 unchanged: (1, 2)
  }

  public static Point triple(Point p) {
    p = new Point(p.x * 3, p.y * 3); // Redirect p
    return(p);
  }

  public static void print(String name, Point p) {
    System.out.println("Point " + name + "= (" +
                       p.x + ", " + p.y + ").");
  }
}

/** Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

interface Barking {}

class Mammal {}

class Canine extends Mammal {}

class Dog extends Canine implements Barking {}

class Retriever extends Dog {}

public class InstanceOf {
  public static void main(String[] args) {
    Canine wolf = new Canine();
    Retriever rover = new Retriever();

    System.out.println("Testing instanceof:");
    report(wolf, "wolf");
    System.out.println();
    report(rover, "rover");

    System.out.println("\nTesting isInstance:");
    Class barkingClass = Barking.class;
    Class dogClass = Dog.class;
    Class retrieverClass = Retriever.class;
    System.out.println("  Does a retriever bark? " +
                       barkingClass.isInstance(rover));
    System.out.println("  Is a retriever a dog? " +
                       dogClass.isInstance(rover));
    System.out.println("  Is a dog necessarily a retriever? " +
                       retrieverClass.isInstance(new Dog()));
  }

  public static void report(Object object, String name) {
    System.out.println("  " + name + " is a mammal: " +
                       (object instanceof Mammal));
    System.out.println("  " + name + " is a canine: " +
                       (object instanceof Canine));
    System.out.println("  " + name + " is a dog: " +
                       (object instanceof Dog));
    System.out.println("  " + name + " is a retriever: " +
                       (object instanceof Retriever));
  }
}

/** Taken from Core Web Programming from 
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.  
 */
 
 // Further simplified getURL method. 
 
 public URL getURL() {
    if (url != null) {
      return(url);
    }
    System.out.print("Enter URL: ");
    System.out.flush();
    BufferedReader in = new BufferedReader(
                          new InputStreamReader(System.in));
    String urlString = null;
    try {
      urlString = in.readLine();
      url = new URL(urlString);
    } catch(MalformedURLException mue) {
      System.out.println(urlString + " is not valid.\n" +
                                 "Try again.");
      getURL();
    } catch(IOException ioe) {
      System.out.println("IOError when reading input: " + ioe);
      ioe.printStackTrace(); // Can skip return(null) now
    } finally {
      return(url);
    }
  }

import java.net.*; // For URL, MalformedURLException
import java.io.*;  // For BufferedReader

/** A small class to demonstrate try/catch blocks.
 *
 *  Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

public class URLTest {
  public static void main(String[] args) {
    URLTest test = new URLTest();
    test.getURL();
    test.printURL();
  }

  private URL url = null;

  /** Read a string from user and create a URL from it. If
   *  reading fails, give up and report error. If reading
   *  succeeds but URL is illegal, try again.
   */

  public URL getURL() {
    if (url != null) {
      return(url);
    }
    System.out.print("Enter URL: ");
    System.out.flush();
    BufferedReader in = new BufferedReader(
                          new InputStreamReader(System.in));
    String urlString;
    try {
      urlString = in.readLine();
    } catch(IOException ioe) {
      System.out.println("IOError when reading input: " + ioe);
      ioe.printStackTrace(); // Show stack dump.
      return(null);
    }
    try {
      url = new URL(urlString);
    } catch(MalformedURLException mue) {
      System.out.println(urlString + " is not valid.\n" +
                         "Try again.");
      getURL();
    }
    return(url);
  }

  /** Print info on URL. */

  public void printURL() {
    if (url == null) {
      System.out.println("No URL.");
    } else {
      String protocol = url.getProtocol();
      String host = url.getHost();
      int port = url.getPort();
      if (protocol.equals("http") && (port == -1)) {
        port = 80;
      }
      String file = url.getFile();
      System.out.println("Protocol: " + protocol +
                         "\nHost: " + host +
                         "\nPort: " + port +
                         "\nFile: " + file);
    }
  }
}

/** Taken from Core Web Programming from 
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.  
 */
 
  // Simplified getURL method.
  
  public URL getURL() {
    if (url != null) {
      return(url);
    }
    System.out.print("Enter URL: ");
    System.out.flush();
    BufferedReader in = new BufferedReader(
                          new InputStreamReader(System.in));
    String urlString = null;
    try {
      urlString = in.readLine();
      url = new URL(urlString);
    } catch(MalformedURLException mue) {
      System.out.println(urlString + " is not valid.\n" +
                                    "Try again.");
      getURL();
    } catch(IOException ioe) {
      System.out.println("IOError when reading input: " + ioe);
      ioe.printStackTrace(); // Show stack dump
      return(null);
    }
    return(url);
  }

/** A test of the Exec class.
 *
 *  Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

public class ExecTest {
  public static void main(String[] args) {
    // Note: no trailing "&" -- special shell chars not
    // understood, since no shell started. Besides, exec
    // doesn?t wait, so the program continues along even
    // before Netscape pops up.
    Exec.exec("/usr/local/bin/netscape");

    // Run commands, printing results.
    Exec.execPrint("/usr/bin/ls");
    Exec.execPrint("/usr/bin/cat Test.java");

    // Don?t print results, but wait until this finishes.
    Exec.execWait("/usr/java1.3/bin/javac Test.java");

    // Now Test.class should exist.
    Exec.execPrint("/usr/bin/ls");
  }
}