COMP 110: Introduction to Programming Tyler Johnson Apr 20, 2009 MWF 11:00AM-12:15PM Sitterson 014

COMP 110:Introduction to Programming

Tyler JohnsonApr 20, 2009

MWF 11:00AM-12:15PMSitterson 014

COMP 110: Spring 20092

Announcements

Lab 8 has been graded

Milestone 1 has been graded

COMP 110: Spring 20093

Questions?

COMP 110: Spring 20094

Today in COMP 110

Go over Lab 8

Java Graphics

Programming Demo

COMP 110: Spring 20095

Lab 8

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Computer Graphics

Computer Graphics is about producing images with a computer

This can be useful in a variety of ways

User interfaces (dialog boxes, icons, windows)Special effects (movies, games, etc)Image editing (photoshop)Visualizing scientific data

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Graphics in Java

Java provides some useful classes & functionality for adding graphics to your programs

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Your First Graphics Program

import javax.swing.JApplet;import java.awt.Graphics;

public class HappyFace extends JApplet {

public void paint(Graphics canvas) {

canvas.drawOval(100, 50, 200, 200);canvas.fillOval(155, 100, 10, 20);canvas.fillOval(230, 100, 10, 20);canvas.drawArc(150, 160, 100, 50, 180, 180);

}}

Where’s the main method?

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Applets

public class HappyFace extends JApplet

Our HappyFace class inherits from the class JApplet

This means that our program is an applet instead of a normal application

An applet is program that is meant to be run in a web browser

We’ll use it as an easy way to get some graphics capability

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Applets

Applets do not have a main methodThey can’t be run like a normal application (using the red running man icon in jGRASPWe need to use the apple icon to run the applet

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Drawing to Screen

public void paint(Graphics canvas) {

canvas.drawOval(100, 50, 200, 200);canvas.fillOval(155, 100, 10, 20);canvas.fillOval(230, 100, 10, 20);canvas.drawArc(150, 160, 100, 50, 180, 180);

}

Applets use a method called paint in order to draw to screen

This method is called for you automatically when you start the applet

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Screen Coordinate System

(0,0)x-

axis

y-

axis

(100,50)

50 pixels

100 pixels

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Drawing Shapes

//draw oval at position 100, 50, of width and height 200canvas.drawOval(100, 50, 200, 200);

//draw a “filled-in” oval at position 155, 100 with w=10, h=20canvas.fillOval(155, 100, 10, 20);

//draw a “filled-in” oval at position x=230, y=100 with w=10, h=20canvas.fillOval(230, 100, 10, 20);

//draw an arc, details in the text on pgs 33-34canvas.drawArc(150, 160, 100, 50, 180, 180);

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The Graphics Class

What is the canvas object?An object of the Graphics class

The graphics class knows how to draw things like shapes to the screen

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Setting the Color

The Graphics class also provides the capability to change the color that shapes are drawn with

Example//draw a yellow ovalcanvas.setColor(Color.YELLOW);canvas.drawOval(100, 50, 200, 200);

//now draw a black ovalcanvas.setColor(Color.BLACK);canvas.drawOval(100, 50, 200, 200);

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Drawing Text to the Screen

We can display text on the screen using the drawString method

drawString(string, xPos, yPos)

Example

//print at string and position (60, 75)canvas.drawString("This will be printed to the screen", 60, 75);

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String Drawing Example

import javax.swing.JApplet;import java.awt.Graphics;

public class HappyFace extends JApplet {

public void paint(Graphics canvas) {

canvas.drawOval(100, 50, 200, 200);canvas.fillOval(155, 100, 10, 20);canvas.fillOval(230, 100, 10, 20);canvas.drawArc(150, 160, 100, 50, 180, 180);

canvas.drawString("This is a happy face!", 50, 50);}

}

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Drawing Polygons

A polygon is a closed figure made up of line segments that do NOT cross

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Drawing Polygons

You can draw a polygon by giving the locations of the corners

There are two functions you can usedrawPolygon• Draws an unfilled polygon (just the edges)

fillPolygon• Draw a filled polygon

p1

p2

p3p4

p5

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Drawing Polygons

Syntaxcanvas.drawPolygon(X_Array, Y_Array, Num_Points)canvas.fillPolygon(X_Array, Y_Array, Num_Points)

Example

int[] xHouse = {150, 150, 200, 250, 250};int[] yHouse = {100, 40, 20, 40, 100};

canvas.drawPolygon(xHouse, yHouse, xHouse.length);

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Creating Dialog Boxes

Dialog boxes are special windows that can be used to take input from the user or to display output

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Dialog Boxes

Dialog boxes can be created using the JOptionPane classimport javax.swing.JOptionPane;

public class JOptionPaneDemo {

public static void main(String[] args) {

String name = JOptionPane.showInputDialog("Enter your name:");

JOptionPane.showMessageDialog(null, "Hi " + name + "!"); System.exit(0);}

}

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Input Dialogs

Input dialogs take input from the user in the form of a string

We use the showInputDialog method of the JOptionPane class

ExampleString name = JOptionPane.showInputDialog("Enter your

name:")

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Output Dialogs

Output dialogs are used to display a message to the user

We use the showMessageDialog method of the JOptionPane class

ExampleJOptionPane.showMessageDialog(null, "Hi " + name + "!");

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Methods of JOptionPane

If showInputDialog and showMessage Dialog are called using the class name JOptionPane, what kind of methods must they be?

Static, a JOptionPane object is never created

String name = JOptionPane.showInputDialog("Enter your name:");

JOptionPane.showMessageDialog(null, "Hi " + name + "!");

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Exiting the Program

public static void main(String[] args) {

String name = JOptionPane.showInputDialog("Enter your name:"); JOptionPane.showMessageDialog(null, "Hi " + name + "!"); System.exit(0);}

At the end of the program we called System.exit(0)

This is necessary to get the program end when using things like windows/dialog boxes etc.

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Confirmation Windows

We can also create dialog boxes that provide the user with the options “Yes” and “No”

These are called confirmation windows

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Confirmation Windows

import javax.swing.JOptionPane;

public class JOptionPaneDemo2 {

public static void main(String[] args) {

while(true) {

int answer = JOptionPane.showConfirmDialog(null, "End Program?",

"Click Yes or No:", JOptionPane.YES_NO_OPTION);

if(answer == JOptionPane.YES_OPTION) System.exit(0); else if(answer == JOptionPane.NO_OPTION) System.out.println("One more time"); else System.out.println("Error");

} }}

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Creating the Window

int answer = JOptionPane.showConfirmDialog(null, "End Program?",

"Click Yes or No:", JOptionPane.YES_NO_OPTION);

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Checking the Result

if(answer == JOptionPane.YES_OPTION)System.exit(0);

else if(answer == JOptionPane.NO_OPTION)System.out.println("One more time");

elseSystem.out.println("Error");

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Programming Demo

Improving our HouseFill the house with a colorDraw a doorDraw a window

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Programming Demo

(150, 100)

(150, 40)

(200, 20)

(250, 40)

(250, 100)

(0,0)x-

axis

y-

axis

(175, 100)

(175, 60) (200, 60)

(200, 100)

(220, 60)

(220, 80)

(240, 80)

(240, 60)

(150, 120)

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Programming Demo

Programming

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Wednesday

Begin reviewing for final