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Applications of Java to Physics Teaching (Part I)

Applications of Java to Physics Teaching (Part I). S S Tong Department of Physics CUHK. 1 Interactive Teaching in Physics. IT development in HK Arose students’ interest Truly interactive? Illustrate both Phy. & Maths. concepts? Supplements to experiments. 2 Why Java?.

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Applications of Java to Physics Teaching (Part I)

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  1. Applications of Java to Physics Teaching (Part I) S S Tong Department of Physics CUHK

  2. 1 Interactive Teaching in Physics • IT development in HK • Arose students’ interest • Truly interactive? • Illustrate both Phy. & Maths. concepts? • Supplements to experiments

  3. 2 Why Java? • Programs readily distributed on WWW • Run on browsers’ machines • Minimize servers’ loading • Protect servers against hackers • Small, fast download • Portable, platform independent • On PCs, Mac, Workstations • Quite easy to learn

  4. 3. Java Applets for Teaching Physics • Wang F K (NTNU) • http://www.fed.cuhk.edu.hk/sci_lab/ntnujava/ • http://www.phy.ntnu.edu.tw/demolab/index.html • http://www.phy.ntnu.edu.tw/java/index.html • Physics 2000 • http://www.colorado.edu/physics/2000/ • Java LAB • http://physicsweb.org/TIPTOP/VLAB/ • http://www.bekkoame.or.jp/~kamikawa/java_e.htm

  5. Interactive Physics and Math with Java (Sergey Kiselev) • http://www.lightlink.com/sergey/java/index.html • Fowler's Physics Applets (Michael Fowler) • http://www.phys.virginia.edu/classes/109N/more_stuff/Applets/ • Physlet Demonstrations (Wolfgang Christian) • http://WebPhysics.davidson.edu/Applets/Applets.html • Java Applets on Physics (Walter Fendt) • http://home.a-city.de/walter.fendt/physengl/physengl.htm

  6. Example JAVA source codes • Heriot-Watt University Department of Physics • http://www.phy.hw.ac.uk/resources/demos/index.html • Electric charge with JAVA • http://www.dcc.uchile.cl/~sebrodri/JAVA/Proyecto/ProyectI.html • State University of New York at Stony Brook • http://www.dcc.uchile.cl/~sebrodri/JAVA/Proyecto/ProyectI.html

  7. 4. ABC of Java I • Applications: Standalone Java programs • Applets: Programs that run on web browsers • We discuss applets only • How to install Java Development Toolkit (JDK)? • How to edit Java source codes? • How to complie a source file into an applet? • How to insert an applet into an HTML file?

  8. Install JDK • Installation is straightforward • Add a path to the Autoexec.bat • e.g. you installed JDK at c:\jdk1.1.8\ path = c:\jdk1.1.8\bin

  9. Use any text editor to edit a source file • I prefer Textpad • Easily to use clip library • Tools for compiling and running Java programs

  10. Abstract Windowing Toolkit applet package The paint method does the actual paintingjob Example: SayHello.java import java.applet.*; import java.awt.*; public class SayHello extends Applet { Font f = new Font("TimesRoman", Font.BOLD, 36); public void paint(Graphics screen) { screen.setFont(f); screen.setColor(Color.red); screen.drawString("Say Hello", 5, 40); } }

  11. Compile SayHello.java to SayHello.class C:\YourDir\javac SayHello.java SayHello.class Include SayHello.class in a HTML file <HTML> <BODY> <APPLET CODE="SayHello.class" WIDTH=300 HEIGHT=200> </APPLET> </BODY> </HTML> View it by appletviewer The main class C:\YourDir\appletviewer SayHello.html

  12. 4. ABC of Java II • An Object - Oriented (O-O) language • Basic units : Class and Object • The concept of a class • How do we usually classify things? • e.g., Fruit is a class • Attributes : shape, color, etc. • Objects of Fruit : orange, apple, bannna, etc. • e.g., Attributes of an apple : shape is spherical, color is red. • Actual manipulations are done by methods

  13. Class and objects Fruit Individual objects Class (Abstract)

  14. the applet package must be loaded the main class must be a subclass of Applet • The source of a Java applet may look like: import java.applet.*; import ......may have other package public class MyApplet extends Applet { ...... } class ClassA ......{ ...... } class ClassB ......{ ...... } ...... may have other classes

  15. Declare a class called Fruit class Fruit { ...... } • Attributes are described by instance variables class Fruit { String shape, color; boolean eaten; ...... } • Create an object (instance) of Fruit Fruit orange; orange = new Fruit(); • Instance variables of orange can be accessed by orange.shape= “spherical”;

  16. declare the object type assign attributes to orange new object Compiling HelloFruit.class Fruit.class class Fruit { String shape, color; boolean eaten; ...... } • Make a class called fruit • One can now create an object of fruit in an applet import java.applet.*; public class HelloToFruit extends Applet { Fruit orange; pubic void init() { orange = new Fruit(); orange.shape = “spherical”; orange.color = “orange”; orange.eaten = false; } ...... }

  17. this refers to the object calling the constructor class Fruit { String shape, color; boolean eaten; Fruit(String shape, String color, boolean eaten) { this.shape = shape; this.color = color; this.eaten = eaten; } } • A constructor helps to defne a object • Now an object can be created more conveniently: import java.applet.*; public class HelloToFruit2 extends Applet { Fruit orange; public void init() { orange = new Fruit(“spherical”, “orange”, false); } }

  18. import java.awt.*; import java.applet.*; public class HelloToFruit3 extends Applet { Fruit orange = new Fruit("spherical", "orange", true); Font f = new Font( "TimesRoman", Font.BOLD, 36); public void paint(Graphics screen) { screen.setColor(Color.red); screen.setFont(f); screen.drawString("The color of orange is" + " " + orange.color, 5, 20); if (orange.eaten) screen.drawString(“It has been eaten”, 5, 90); } } • Adding the paint method

  19. w (x,y) h Rect(Point p, Point q) { this(p.x, p.y, q.x - p.x, q.y - p.y); } p(x,y) R1 = new Rect(1,1,2,1); Point p1 = new Point(1,1); Point p2 = new Point(3,2); R2 = new Rect(p1,p2); q(x,y) give rectangles of the same size and position • Overloading a constructor import java.awt.*; class Rect { int x, y, w, h; Rect(int x, int y, int w, int h) { this.x = x; this.y = y; this.w = w; this.h = h; } }

  20. argument (no argument here) argument (no argument here) return type (void return nothing) name of method name of method the object which calls the method (a MyClass object here) • Delcaring methods void myMethod() { ........ } • Using methods • suppose myMethod() is declared in MyClass myClassObject.myMethod();

  21. name of method name of method return type (a double here) arguments (takes 1 integer and 1 string) the object which calls the method (a MyNewClass object here) an integer a string return value (must be a double here) a double • Another example double myNewMethod(int t, String s) { ........ return result; } • Calling the method • suppose myNewMethod() is declared in MyNewClass myNewClassObject.myNewMethod(10, “abc”)

  22. return doubles • Using methods (an example in physics) class FallingBall { double x, y, ux, uy; double g = -9.8; FallingBall(double x, double y, double ux, double uy) { this.x = x; this.y = y; this.ux = ux; this.uy = uy; } double xt(double t) { return x + ux*t;} double yt(double t) { return y + uy*t + 0.5*g*t*t;} double uxt(double t) { return ux;} double uyt(double t) { return uy + g*t;} }

  23. becomes doubles ( real numbers) • Using methods (continued) : import java.applet.*; import java.awt.*; public class MyFallingBall extends Applet { FallingBall myBall; myBall = newBall(0,0,5,5); ...... public void paint(Graphics screen) { ...... screen.drawString(“After 1s, the ball is at ”, 5, 20); screen.drawString(“x = “ + myBall.xt(1) + “, y = “ + myBall.yt(1), 5, 30); ...... } }

  24. true or false w of the object (R1) which calls the method w of the argument (R2) • Using methods (another example) ...... public class MyRect2 extends Applet { ...... ...... R1.equals(R2) ......; ...... } class Rect { ...... boolean equals(Rect R) { return (R.x == x) && (R.y == y) && (R.w == w) && (R.h == h); } }

  25. (two doubles) (called by a vector object, returning a double) (called by a vector object, taking a vector argument, returning a vector object) e.g. vectorA.add(vectorB) • Exercise 1 (Vector.java) : Contructor : x and y-compoents of a vector Contructor : How about polar coordinates? Method 1 : find the magnitude of a vector Method 2 : add two vectors Method 3 : subtract two vectors Method 4 : find the dot product of two vectors (called by a vector object, taking a vector argument, returning a double)

  26. 0 to3 • Array objects • declare an array String[] Names = new String[4]; • access individual elements Names[0] = “Put your name here”; Names[1] = “Tong Shiu-sing”; ........ Names[3] = “Doraemon”; • may also declare and initialize an array by String[] Names = {“Your name here”, “Tong Shiu-sing”,......, “Doraemon”}; • assigning values to elements screen.drawString(Names[3]);

  27. e.g.1 if (Names[3] == “Doraemon”) currentString = “I am Doraemon”; e.g.2 if (Names[3].length > 15) currentString = “a long name”; else currentString = “a short name”; e.g.3 if (Names[1] == “Doraemon”) { ........ } else if (Names[1] == “Tong Shiu-sing”) { ........ } else { ........ } || != && == • Logic and loops • logical operators > < >= <= • conditional statements • if - then blocks

  28. i  i + 1 e.g 4 for (int i = 0; i < 4; i++) { if (Names[i].length() > 15) currentString = “a long name”; else currentString = “a short name”; ........ } e.g.5 i = 0; while (Name[i] != “Doraemon”) { i++; } currentString = “Doraemon is at position ” + i; • for loop • while loop

  29. Subclasses of Food Subclasses of Meat Chicken Instances of warm blooded meat Beef Pork • Inheritance of classes Food Meat Vegetable Fruit Cold blooded Warm blooded

  30. Inheritance of classes (an example in physics) • Declare a class Ball class Ball { double x, y, radius; Ball(double x, double y, double radius) { this.x = x; this.y = y; this.radius = radius; } }

  31. Call the constructor of its superclass • Inheritance of classes (continued) • A subclass MovingBall carries more information • It also contains methods class MovingBall extends Ball { double ux, uy; MovingBall(double x, double y, double ux, double uy, double radius) { super(x, y, radius); this.ux = ux; this.uy = uy; } double xt(double t) { return x + ux*t;} double yt(double t) { return y + uy*t;} }

  32. Call the constructor of its superclass Override its superclass’s method • Inheritance of classes (continued) • A subclass FallingBall of MovingBall class FallingBall extends MovingBall { double gy; FallingBall (double x, double y, double ux, double uy, double gy, double radius) { super(x, y, ux, uy, radius); this.gy = gy; } double yt(double t) { return y + uy*t + gy*t*t/2;} }

  33. ballA.xt(2) gives x + ux*t = 0 + 3*2 = 6 ballA.yt(2) gives y + uy*t = 0 + 5*2 = 10 ballB.xt(2) still gives x + ux*t = 0 + 3*2 = 6 call to the xt method of in MovingBall ballB.yt(2) Now gives y + uy*t + ay*t*t/2 = 0 + 5*2 - 10*2*2/2 = -10 the method yt is overridden • Inheritance of classes (continued) MovingBall ballA = new MovingBall(0,0,3,5,1); FallingBall ballB = new FallingBall(0,0,3,5,-10,1);

  34. Class A ABC(...) Class C Class D object object A method calls to the superclass ABC Going up the chain of inheritance until a definition of the method ABC is found ABC ABC Class B A method ABC is called

  35. Class A ABC(...) Class B ABC(...) Class C Class D object object A method is overridden by another method of the same name ABC Going up the chain of inheritance, the first reached ABC is executed ABC A method ABC is called

  36. Class A ABC(...) ABC(...) calls ABC in this class Class B super.ABC(...) ABC(...) calls ABC in the superclass Calling a overridden method in a superclass Initial method definition Method overriden by subclass

  37. Exercise 2 (Waves) • Construct a class of sine curve (only variable: amplitude, create a method y(x) ) • Construct a class of traveling waves (2 more variables: wavelength, period, create y(x,t) making use of the superclass’s y(x) ) • Construct a class of standing waves (any more variables needed?, think of a standing wave as a superposition of 2 waves traveling in opposite direction, create y(x,t) making use of the superclass’s y(x,t) )

  38. 5. ABC of Java III • Graphics coordinate system (0,0) x (20, 20) (60, 60) y

  39. begin point end point Graphics object screen.drawRect(x, y, w, h); / fillRect upper-left corner width height x, y coordinates of corners int[] x = {10,20,30,10}, y = {0,20,10,0}; Polygon poly = new Polygon(x,y,x.length); screen.drawPolygon(poly); make a Polygon object / fillPolygon • Various graphics commands screen.drawLine(x1, y1, x2, y2);

  40. screen.drawOval(x, y, w, h); screen.drawArc(x, y, w, h, t1, t2); (x, y) / fillOval / fillArc h w (x,y) t1 = 90 h t2 = 360 w • Various graphics commands (continued)

  41. Implementing the paint method import java.awt.*; import java.applet.*; public class DrawSomething extends Applet { public void paint(Graphics screen) { screen.setColor(Color.red); screen.drawString( “I am Doraemon”,200,200); screen.drawRect(10,10,120,90); screen.setColor(Color.blue); screen.fillOval(150,10,120,60); screen.setColor(Color.green); screen.drawArc(10,150,120,60,0,270); } }

  42. Image file name get the directory of the applet (here the applet and the image file are in the same directory) upper-left corner • Drawing images • Create an object of Image Image myImage; • Load the image into the applet myImage = getImage(getCodeBase(), “hi.gif”); • Draw the image on screen in the paint method public void paint(Graphics screen) { ...... screen.drawImage(myImage,20,10,this); ...... }

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