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Lecture 2

Lecture 2. Review. To play with Turtle, we need to download and install followings: JDK 6 Dr. Java Sample program (e.g. BookClass). JDK 6. Java Development Kit (version 6) It contains several tools, required to write and test Java applications You may download

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Lecture 2

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  1. Lecture 2

  2. Review • To play with Turtle, we need to download and install followings: • JDK 6 • Dr. Java • Sample program (e.g. BookClass)

  3. JDK 6 • Java Development Kit (version 6) • It contains several tools, required to write and test Java applications • You may download Windows Platform - Java(TM) SE Development Kit 6 http://java.sun.com/javase/downloads/index.jsp Note: It is already installed in PC at computer lab

  4. Dr. Java • It is a software application, called IDE (Integrated Development Environment) • It supports us to develop an application • It provides GUI builder, a text/program editor, compiler, and debugger, etc. For example Visual Studio, JBuilder, FrontPage and DreamWeaver • You may download Windows App http://drjava.org/

  5. Sample Program • Sample program contains Java program, which enable us to play with Turtle • You may download bookClasses-8-21-06.zip http://coweb.cc.gatech.edu/mediaComp-plan/101 • You have to extract the zip file into a directory For example, you can create a directory named “BookClass”, and extract files into the directory

  6. And then … • After open Dr.Java, you have to tell Dr. Java where the sample program is 1 SelectEdit -> Preference 2 Click Add and specifythe directory of BookClass

  7. Don’t forget Homework 0 • Be prepare for doing homework and projectsat both computer lab and home !!!

  8. Today • Let’s talk about • Object • Class • Instance • Method • Statement

  9. Creating objects World w1 = new World() 640 Create a new world, named w1 - This creates a window whose size is 640x480 pixels 480

  10. Creating objects Turtle t1 = new Turtle(w1) Create a turtle, named t1, in the world w1 - as a default, a turtle is located at the center where? (320, 240)

  11. Creating objects You can create many worlds and turtles World w1 = new World() World w2 = new World() Turtle t1 = new Turtle(w1) Turtle t2 = new Turtle(w2) Turtle t3 = new Turtle(w1) W1 W2 T1, T3 T2

  12. What is an object • In real world • Dog, Book, Cell phone, etc. • Each object has a state and a behavior For example, Dog • State – He has name, color, breed, etc. • Behavior – He is barking, wagging, etc. • The world is viewed as a collection of objects • Similarly, in Java programming world • Object contains data and operations For example, Turtle t1 • has name (t1) and color (green), etc. • can move, can turn, etc.

  13. Class and Object • For example of phone, there are many types of phones. • To create “your phone” (which is an objects) we need a blueprint to create it. • Let’s call the blueprint PHONE • The blueprint PHONE is called class PHONE • In java, we say that “your phone” is an instanceof class, known as PHONE

  14. Class and Object • Class is like a cookie cutter • Many objects are createdfrom a class • Using the new operator: ClassName name = new ClassName(); • For example Turtle Object 1 Turtle Object 2 Turtle t1 = new Turtle(w1) Turtle: Class

  15. Methods of Turtle A Turtle has a pen A Turtle can take actions such as move and turn While a turtle moves, he draws a line with a pen In Java We call the actions as methods e.g. move forward, and backward, turn right and left, etc.

  16. How to call method ObjectName.MethodName() ObjectName.MethodName(parameter) For example, Turtle t1 = new Turtle(w1) t1.forward() t1.backward() t1.turnRight() t1.turnLeft() t1.forward(200) t1.turn(45) …

  17. Statement Each instruction is called a statement A program is a collection of statements Note: Please remember thatsemi-colon is required at the end of each statement World w1 = new World(); t1.turnLeft();

  18. Lab • Let’s play with Turtle

  19. Warming up!!! • Try to draw a triangle

  20. Practice!!! • Try to draw a pentagon

  21. Practice!!! • Try to draw a pentagon 180 x 3 / 5 = 108 72

  22. Additional methods … penUp() - turtle will grab his pen up penDown() - turtle will put his pen down moveTo(x,y) - turtle will move to a position (x, y)

  23. Additional methods … (more!!!) hide() - turtle will hide from the world show() - turtle will show up again clearPath() - clear all lines in the worldnote: you have to minimize the window setColor( java.awt.Color.xxx ) - turtle will change the pen color - xxx will be RED, BLUE, GREEN, etc

  24. Challenge • Try to draw one triangle and one squarein the world

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