CSCI 053. Week 5 Java is like Alice not based on Joel Adams you may want to take notes. Rhys Price Jones. Introduction to Software Development

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1 CSCI 053 Introduction to Software Development Rhys Price Jones Week 5 Java is like Alice not based on Joel Adams you may want to take notes

2 Objectives Learn to use the Eclipse IDE Integrated Development Environment Learn how to create a Java Applet Learn how to create a Java Application Learn about the java.awt.graphics class Make some nice pictures 2

3 More objectives Learn about mouse listeners make programs that respond to mouse events tell simple stories in Java

4 Eclipse free download an open development platform the beginning of an Eclipse Eclipse is an open source community whose projects are focused on building an open development platform comprised of extensible frameworks, tools and runtimes for building, deploying and managing software across the lifecycle. A large and vibrant ecosystem of major technology vendors, innovative start-ups, universities, research institutions and individuals extend, complement and support the Eclipse platform

5 Start Eclipse It will probably ask you to specify a workspace mine is ~/fall08/cs53/week5workspace Some people like lots of workspaces create new ones in the File menu Some people like just one

6 Go to the Workbench Create a new Project called week5 Create a new package called week5 with source folder week5/src Create a new class called PlainVanillaJApplet with superclass javax.swing.japplet

7 Superclass is like the world you choose in Alice We can choose JApplet JFrame java.lang.object quite dull, but occasionally useful

8 Eclipse generates the code Go ahead and run it: see what works!

9 The PlainVanillaJApplet try the green, yellow, red buttons try to resize

10 We would like something more Make a new class same package, etc... named PlainStrawberryJApplet same superclass javax.swing.japplet add a method public void paint(graphics g)

11 Like this Notes: 1. I clicked the Generate comments box 2. Errors are tagged 3. Click on error flag to see Eclipse s suggestion 4. Double click the first suggestion (import...) 5.Deal with warning similarly 6. Be sure to test the resizing! -- oops!

12 Deal with errors/warnings

13 Eclipse preferences Can be used to get rid of the serialversionuid warning and to improve the generated comments and... many other cool things.

14 Using the API documentation find out what the various widgets can do These are the list of characters many can be added to your JApplet Your program will tell them what to do the API documentation is essential

15 Look again at PlainStrawberryJApplet

16 Where did I find? g.fillrect(...) in the documentation for Graphics getwidth(), getheight() not in JApplet but... a few generations up in java.awt.component

17 Adding text Look in documentation for Graphics drawstring() choice of two choose the simpler! setcolor we know how do we use setfont? Google java setfont example

18 extend PlainStrawberryJApplet2

19 Now play with drawrect fillrect drawoval drawpolygon drawline drawarc etc.

20 Reading images Study the documentation g.drawimage needs an Image, and an ImageObserver How to read an Image from a file? see next slide

21 A Program

22 Things to note public void init() lets me set things like the size... try and catch because we know something could go wrong. Java wants us to specify what to do if it does. The image needs to be called gruff.jpg and reside in the bin folder with JAppletWithImage.class

23 Quizlet 1. A Java JApplet, JFrame, etc is like an Alice because it is where everything is displayed. 2. The method is where you can control how your JApplet will appear 3. The method is where you can specify things like size of JApplet, etc 4. To add text to the JApplet we use the drawstring method of the class. 5. To draw a circle we use the method with the width and height parameters set to the same value.

24 Quizlet Answers 1. A Java JApplet, JFrame, etc is like an Alice world because it is where everything is displayed. 2. The paint method is where you can control how your JApplet will appear 3. The init method is where you can specify things like size of JApplet, etc 4. To add text to the JApplet we use the drawstring method of the Graphics class. 5. To draw a circle we use the drawoval method with the width and height parameters set to the same value.

25 Adding Mouse Interactivity we need a MouseListener object consult the documentation and it needs to be added to what? look for addmouselistener method in JApplet It is inherited from java.awt.component

26 java.awt.component Direct Known Subclasses: Button, Canvas, Checkbox, Choice, Container, Label, List, Scrollbar, TextComponent So any of these can have a MouseListener So can any of their subclasses!

27 Class Hierarchies In addition to the API documentation you can find tools like to help you

28 The JApplet itself can have a MouseListener we can add it in the init() method Now here s the thing...

29 The JApplet itself can be its own MouseListener just so long as you provide the appropriate methods What is appropriate? look at the API documentation for the MouseListener interface

30 What is an interface? A collection of methods In order to implement the interface a class must provide those methods Let s extend PlainStrawberryJApplet2 again but this time say the class will implement MouseListener

31 Eclipse new class superclass: PlainStrawberryJApplet2 Interfaces: MouseListener

34 I called the class ColorChanger because that s what I want to do declare an instance variable Color mycolor = Color.pink; change the paint method so it g.setcolor(mycolor) change the color on a mouse click!

35 The code I wrote private Color mycolor; public void init() { mycolor = Color.pink; } addmouselistener(this); public void paint(graphics g) { g.setcolor(mycolor); g.fillrect(0,0,getwidth(),getheight()); } public void mouseclicked(mouseevent arg0) { } mycolor = Color.green; repaint();

36 What is this? We want the JApplet to be a MouseListener We want to add a MouseListener to the JApplet this is a keyword that lets an object refer to itself We want to add a ColorChanger (as a MouseListener) to the ColorChanger (as a JApplet) addmouselistener(this);

37 or even!!! We want the JApplet to be a MouseListener We want to add a MouseListener to the JApplet this is a keyword that lets an object refer to itself We want to add a ColorChanger (as a MouseListener) to the ColorChanger (as a JApplet) this.addmouselistener(this);

38 in-class Exercise Add comments to the code, then Make it so that when I press the mouse the applet turns green when I release the mouse the applet reverts to pink

39 in-class Exercise 9October We added interactivity to the JAppletWithImage program we saw earlier You need to click to see the dog The background changes color as the mouse enters and exits Program downloadable from class page

40 Quizlet 1. Responding to mouse events requires adding a 1. You can add a MouseListener to any 1. A good place to add a MouseListener to a JApplet is in the method 1. A MouseListener can be any object of any class that implements the interface 2. The keyword lets you refer to the current object

41 1. Quizlet answers 1. Responding to mouse events requires adding a _MouseListener 2. You can add a MouseListener to any _Component 3. A good place to add a MouseListener to a JApplet is in the init method 4. A MouseListener can be any object of any class that implements the _ MouseListener interface 5. The keyword this lets you refer to the current object

TWO-DIMENSIONAL FIGURES

TWO-DIMENSIONAL FIGURES Two-dimensional (D) figures can be rendered by a graphics context. Here are the Graphics methods for drawing draw common figures: java.awt.graphics Methods to Draw Lines, Rectangles