chapter 4: applets and graphics 1 ©2000, john wiley & sons, inc. horstmann/java essentials, 2/e...

©2000, John Wiley & Sons, Inc.Horstmann/Java Essentials, 2/e

Chapter 4: Applets and Graphics1

Chapter 4

Applets and Graphics



Java Programs

• Console application– Plain looking terminal window

• Graphical application– User interface components (buttons, text input)

• Applets– Graphical applications that run inside a web

browser.



Figure 1A Console Application



Figure 2A Graphical Application



Applets

• Web server (Store a code)• Web pages• Browser (downloaded)• Applets are programs that run inside a web

browser.• Advantage: others can access your program

– Multiple platform (java bytecode)

• Disadvantage: download time, security



Figure 3Web Browsers Accessing a WebServer



HTML

• <IMG SRC=“hamster.jpeg” WIDTH=640 HEIGHT=480 ALT=“A photo of Harry, the Horrible Hamster”>

• <A HREF=http://java.sun.com> Java</A> is an object-oriented programming language.

• <APPLET CODE=“HamsterApplet.calss” WIDTH=400 HEIGHT=300>An animation of Harry, the horrible Hamster</APPLET>



A Simple Applet

– <HTML>– <BODY>– <P>Here is my first applet</P>– <APPLET CODE=“RectangleApplet.class”

WIDTH=300 HEIGHT=300>– </BODY>– </HTML>



A Simple Applet

• appletviewer RectangleApplet.html

– public calss RectangleApplet extends Applet– { public void paint(Graphic g)– { …– }– }



A Simple Applet

• Applets don’t have a main method.

• The web browser is responsible for starting up the Java virtual machine.

• Graphics (Object)



Figure 4The Rectangle Applet inthe Applet Viewer



Figure 5The Rectan-gle Applet in aJava 2–EnabledBrowser



Program RectangleApplet.java

import java.applet.Applet;import java.awt.Graphics;import java.awt.Graphics2D;import java.awt.Rectangle;

public class RectangleApplet extends Applet{ public void paint(Graphics g) { // recover Graphics2D

Graphics2D g2 = (Graphics2D)g;

// construct a rectangle and draw it

Rectangle cerealBox = new Rectangle(5, 10, 20, 30); g2.draw(cerealBox);



// move rectangle 15 units sideways and 25 units down

cerealBox.translate(15, 25);

// draw moved rectangle

g2.draw(cerealBox); }}



Graphical Shapes

• Ellips

• Ellipse2D.Double easterEgg = new Ellipse2D.Double(5, 10, 15, 20)

• Import java.awt.geom.Ellipse;

• Line2D.Double segment = new Line2D.Double (x1, y1, x2, y2);



Figure 6An Ellipse and ItsBounding Box



Colors

• RGB

• Color magenta = new Color(1.0F, 0.0F, 1.0F);

• P152



Fonts

• G2.drawString(“Applet”, 50, 100);• final int HUGE_SIZE = 36;• String message = “Applet”;• Font hugeFont = new Font (“Serif”, Font. Bold,

Huge_SIZE);• g2.setFont(hugeFont);• g2.setColor(Color.pint);• g2.drawString(message, 50, 100);



Figure 7Basepoint and Baseline



Figure 8Common Fonts



Figure 9Text Layout



Figure 10The Font Applet



Program FontApplet.java

import java.applet.Applet;import java.awt.Graphics;import java.awt.Graphics2D;import java.awt.Font;import java.awt.font.FontRenderContext;import java.awt.font.TextLayout;

public class FontApplet extends Applet{ public void paint(Graphics g) { Graphics2D g2 = (Graphics2D)g;

// select the font into the graphics context

final int HUGE_SIZE = 48; Font hugeFont = new Font("Serif", Font.BOLD, HUGE_SIZE); g2.setFont(hugeFont);

String message ="Applet";



// create a text layout to measure the string

FontRenderContext context = g2.getFontRenderContext(); TextLayout layout = new TextLayout(message, hugeFont, context);

// measure the message width and height

float xMessageWidth = layout.getAdvance(); float yMessageHeight = layout.getAscent() + layout.getDescent();

// center the message in the window float xLeft = 0.5F * (getWidth()- xMessageWidth); float yTop = 0.5F * (getHeight()- yMessageHeight); float yBase = yTop + layout.getAscent();

g2.drawString(message, xLeft, yBase); }}



Simple Drawings

• Car drawings



Figure 11A Graphical Applet ThatDraws a Sketch of a Car



Program CarDrawer.java

import java.applet.Applet;import java.awt.Graphics;import java.awt.Graphics2D;import java.awt.Rectangle;import java.awt.geom.Ellipse2D;import java.awt.geom.Line2D;import java.awt.geom.Point2D;

public class CarDrawer extends Applet{ public void paint(Graphics g) { Graphics2D g2 = (Graphics2D)g;

Rectangle body = new Rectangle(100, 110, 60, 10);

Ellipse2D.Double frontTire = new Ellipse2D.Double(110, 120, 10, 10); Ellipse2D.Double rearTire = new Ellipse2D.Double(140, 120, 10, 10);



Point2D.Double r1 = new Point2D.Double(110, 110); // the bottom of the front windshield Point2D.Double r2 = new Point2D.Double(120, 100); // the front of the roof Point2D.Double r3 = new Point2D.Double(140, 100); // the rear of the roof Point2D.Double r4 = new Point2D.Double(150, 110); // the bottom of the rear windshield

Line2D.Double frontWindshield = new Line2D.Double(r1, r2); Line2D.Double roofTop = new Line2D.Double(r2, r3); Line2D.Double rearWindshield = new Line2D.Double(r3, r4);



g2.draw(body); g2.draw(frontTire); g2.draw(rearTire); g2.draw(frontWindshield); g2.draw(roofTop); g2.draw(rearWindshield);

g2.drawString("JavaMobile 1.2ti", 100, 150); }}



Figure 12Using Graph Paper to Find ShapeCoordinates



Figure 13Diagrams



Figure 14Scene



Figure 15Manipulated Image



Reading Text Input

• JOptionPane calss• showInputDialog method• Javax.swing package

• String input = JOPtionPane.shwInputDialog(“Please enter your age:”);

• int age = Integer.parseInt(input);\



Figure 16An Input Dialog



Program ColorSelect.java

import java.applet.Applet;import java.awt.Color;import java.awt.Graphics;import java.awt.Graphics2D;import java.awt.Rectangle;import javax.swing.JOptionPane;

public class ColorSelect extends Applet{ public void init() { String input;

// ask the user for red, green, blue values

input = JOptionPane.showInputDialog("red:"); float red = Float.parseFloat(input);

input = JOptionPane.showInputDialog("green:"); float green = Float.parseFloat(input);

input = JOptionPane.showInputDialog("blue:"); float blue = Float.parseFloat(input); fillColor = new Color(red,green,blue); }



public void paint(Graphics g) { final int SQUARE_LENGTH = 100;

Graphics2D g2 = (Graphics2D)g;

// select color into graphics context

g2.setColor(fillColor);

// construct and fill a square whose center is // the center of the window Rectangle square = new Rectangle( (getWidth() - SQUARE_LENGTH) / 2, (getHeight() - SQUARE_LENGTH) / 2, SQUARE_LENGTH, SQUARE_LENGTH);

g2.fill(square); }

private color fillColor;}



Figure 17Intersection of a Line anda Circle



Program Intersect.java

import java.applet.Applet;import java.awt.Graphics;import java.awt.Graphics2D; import java.awt.geom.Ellipse2D;import java.awt.geom.Line2D;import javax.swing.JOptionPane;

public class Intersect extends Applet{ public void init() { String input = JOptionPane.showInputDialog("x:"); x = Integer.parseInt(input);}

public void paint(Graphics g){ Graphics2D g2 = (Graphics2D)g;

double r = 100; // the radius of the circle

// draw the circle



Ellipse2D.Double circle = new Ellipse2D.Double(0, 0, 2 * r, 2 * r); g2.draw(circle);

// draw the vertical line

Line2D.Double line = new Line2D.Double(x, 0, x, 2 * r); g2.draw(line);

// compute the intersection points

double a = r; double b = r;



double root = Math.sqrt(r * r - (x - a) * (x - a)); double y1 = b + root; double y2 = b - root;

// draw the intersection points

final double SMALL_CIRCLE_RADIUS = 2;

Ellipse2D.Double circle1 = new Ellipse2D.Double( x - SMALL_CIRCLE_RADIUS, y1 - SMALL_CIRCLE_RADIUS, 2 * SMALL_CIRCLE_RADIUS, 2 * SMALL_CIRCLE_RADIUS); Ellipse2D.Double circle2 = new Ellipse2D.Double( x - SMALL_CIRCLE_RADIUS, y2 - SMALL_CIRCLE_RADIUS, 2 * SMALL_CIRCLE_RADIUS, 2 * SMALL_CIRCLE_RADIUS);



g2.draw(circle1); g2.draw(circle2);

// label the intersection points

String label1 = "” + y1; String label2 = "” + y2;

g2.drawString(label1, (float)x, (float)y1); g2.drawString(label2, (float)x, (float)y2);

}

private double x;

}



Program Phoenix.java

import java.applet.Applet;import java.awt.Graphics;import java.awt.Graphics2D;import java.awt.Rectangle;

public class Phoenix extends Applet{ public void paint(Graphics g) { Graphics2D g2 = (Graphics2D)g; month = 0; units = new UnitConverter(0, 12, 0, 40, getWidth(), getHeight()); final int JAN_TEMP = 11; final int FEB_TEMP = 13; final int MAR_TEMP = 16; final int APR_TEMP = 20; final int MAY_TEMP = 25; final int JUN_TEMP = 31; final int JUL_TEMP = 33; final int AUG_TEMP = 32; final int SEP_TEMP = 29;



final int OCT_TEMP = 23; final int NOV_TEMP = 16; final int DEC_TEMP = 12;

drawBar(g2, JAN_TEMP); drawBar(g2, FEB_TEMP); drawBar(g2, MAR_TEMP); drawBar(g2, APR_TEMP); drawBar(g2, MAY_TEMP); drawBar(g2, JUN_TEMP); drawBar(g2, JUL_TEMP); drawBar(g2, AUG_TEMP); drawBar(g2, SEP_TEMP); drawBar(g2, OCT_TEMP); drawBar(g2, NOV_TEMP); drawBar(g2, DEC_TEMP);}



public void drawBar(Graphics2D g2, int temperature) { // construct rectangle for this month and temperature

Rectangle rect = new Rectangle(month, 0, 1, temperature); // convert to pixel coordinates and draw

units.convert(rect); g2.draw(rect);

month++; }

private int month; private UnitConverter units;}



Figure 18Plotting Temperature Data



Figure 19A Tic-Tac-ToeBoard

chapter 4: applets and graphics 1 ©2000, john wiley & sons, inc. horstmann/java essentials, 2/e...

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