Lecture 2

Review To play with Turtle, we need to download and install followings: 1.JDK 6 2.Dr. Java 3.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 Windows Platform - Java(TM) SE Development Kit 6 Note: It is already installed in PC at computer lab

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

Sample Program Sample program contains Java program, which enable us to play with Turtle –You may download bookClasses zip –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

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

Don’t forget Homework 0 –Be prepare for doing homework and projects at both computer lab and home !!!

Today Let’s talk about –Object –Class –Instance –Method –Statement

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

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)

Creating objects World w1 = new World() World w2 = new World() Turtle t1 = new Turtle(w1) Turtle t2 = new Turtle(w2) Turtle t3 = new Turtle(w1) You can create many worlds and turtles W1W2 T1, T3T2

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.

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 In java, we say that “your phone” is an instance of class, known as PHONE PHONE

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

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.

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

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

Lab –Let’s play with Turtle

Warming up!!! Try to draw a triangle

Practice!!! Try to draw a pentagon

Practice!!! Try to draw a pentagon x 3 / 5 =

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)

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

Challenge Try to draw one triangle and one square in the world