Java Applet and Graphics

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Java Applet & Graphics
Java Applet
Java Graphics
Analog Clock
Prepared By: Khosrow Kian
Edited By: Abdul Rahman Sherzad

Table of Contents
»Java Applet
˃Introduction and Concept
˃Demos
»Graphics
˃Introduction and Concept
»Java Applet Code
2

Java Applet
»An applet is a subclass of Panel
˃It is a container which can hold GUI components
˃It has a graphics context which can be used to draw images
»An applet embedded within an HTML page
˃Applets are defined using the <applet> tag
˃Its size and location are defined within the tag
»Java Virtual Machine is required for the browsers to execute the applet
3

Java Applets vs. Applications
»Applets - Java programs that can run over the Internet using a browser.
˃The browser either contains a JVM (Java Virtual Machine) or loads the Java plugin
˃Applets do not require a main(), but in general will have a paint().
˃An Applet also requires an HTML file before it can be executed.
˃Java Applets are also compiled using the javac command, but are run either with a browser or with the applet viewer command.
»Applications - Java programs that run directly on your machine.
˃Applications must have a main().
˃Java applications are compiled using the javac command and run using the java command.
4

Java Applets vs. Applications
Feature
Application
Applet
main() method
Present
Not present
Execution
Requires JRE
Requires a browser like Chrome, Firefox, IE, Safari, Opera, etc.
Nature
Called as stand-alone application as application can be executed from command prompt
Requires some third party tool help like a browser to execute
Restrictions
Can access any data or software available on the system
cannot access any thing on the system except browser’s services
Security
Does not require any security
Requires highest security for the system as they are untrusted
5

Java Applet Advantages
»Execution of applets is easy in a Web browser and does not require any installation or deployment procedure in real-time programming.
»Writing and displaying (just opening in a browser) graphics and animations is easier than applications.
»In GUI development, constructor, size of frame, window closing code etc. are not required.
6

Java Applet Methods
»init()
˃Called when applet is loaded onto user’s machine.
»start()
˃Called when applet becomes visible (page called up).
»stop()
˃Called when applet becomes hidden (page loses focus).
»destroy()
˃Guaranteed to be called when browser shuts down.
7

Introduction to Java Graphics
»Java contains support for graphics that enable programmers to visually enhance applications
»Java contains many more sophisticated drawing capabilities as part of the Java 2D API
˃Color
˃Font and FontMetrics
˃Graphics2D
˃Polygon
˃BasicStroke
˃GradientPaint and TexturePaint
˃Java 2D shape classes
8

9

Java Coordinate System
»Upper-Left Corner of a GUI component has the coordinates (0, 0)
»X-Coordinate (horizontal coordinate)
˃horizontal distance moving right from the left of the screen
»Y-Coordinate (vertical coordinate)
˃vertical distance moving down from the top of the screen
»Coordinate units are measured in pixels.
˃A pixel is a display monitor’s smallest unit of resolution.
10

All Roads Lead to JComponent
»Every Swing object inherits from JComponent
» JComponent has a few methods that can be overridden in order to draw special things
˃public void paint(Graphics g)
˃public void paintComponent(Graphics g)
˃public void repaint()
»So if we want custom drawing, we take any JComponent and extend it...
˃JPanel is a good choice
11

Draw Line Example
import java.awt.Graphics;
import javax.swing.JApplet;
public class DrawLine extends JApplet {
@Override
public void init() {
}
public void paint(Graphics g){
g.drawLine(20,20, 100,100);
}
}
12

Draw Rectangles Example
public class DrawRect extends JApplet {
@Override
super.init();
}
public void paint(Graphics g) {
g.drawRect(20, 20, 100, 100);
g.fillRect(130, 20, 100, 100);
g.drawRoundRect(240, 20, 100, 100, 10, 10);
}
}
13

Draw Ovals Example
public class DrawOval extends JApplet {
@Override
}
g.drawOval(20, 20, 100, 100);
g.fillOval(130, 20, 100, 100);
}
}
14

Simple Calculator Example
import java.applet.Applet;
import java.awt.BorderLayout;
import java.awt.Button;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.Panel;
import java.awt.TextField;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class Calculator extends Applet implements ActionListener {
String operators[] = { "+", "-", "*", "/", "=", "C" };
String operator = "";
int previousValue = 0;
Button buttons[] = new Button[16];
TextField txtResult = new TextField(10);
15

setLayout(new BorderLayout());
add(txtResult, "North");
txtResult.setText("0");
Panel p = new Panel();
p.setLayout(new GridLayout(4, 4));
for (int i = 0; i < 16; i++) {
if (i < 10) {
buttons[i] = new Button(String.valueOf(i));
} else {
buttons[i] = new Button(operators[i % 10]);
}
buttons[i].setFont(new Font("Verdana", Font.BOLD, 18));
p.add(buttons[i]);
add(p, "Center");
buttons[i].addActionListener(this);
}
}
16

public void actionPerformed(ActionEvent ae) {
int result = 0;
String caption = ae.getActionCommand();
int currentValue = Integer.parseInt(txtResult.getText());
if (caption.equals("C")) {
previousValue = 0;
currentValue = 0;
result = 0;
operator = "";
} else if (caption.equals("=")) {
result = 0;
if (operator == "+")
result = previousValue + currentValue;
else if (operator == "-")
result = previousValue - currentValue;
else if (operator == "*")
result = previousValue * currentValue;
else if (operator == "/")
result = previousValue / currentValue;
txtResult.setText(String.valueOf(result));
}
17

End - Simple Calculator Example
else if (caption.equals("+") || caption.equals("-")
|| caption.equals("*") || caption.equals("/")) {
previousValue = currentValue;
operator = caption;
} else {
int value = currentValue * 10 + Integer.parseInt(caption);
txtResult.setText(String.valueOf(value));
}
}
}
18

OUTPUT - Simple Calculator Example
19

Example of Graphics and Applet
20

Analog Clock Example
21
import java.applet.Applet;
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.util.Calendar;
public class AnalogClock extends Applet implements Runnable {
private static final long serialVersionUID = 1L;
private static final double TWO_PI = 2.0 * Math.PI;
private Calendar nw = Calendar.getInstance();
int width = 200, hight = 200;
int xcent = width / 2, ycent = hight / 2;
int minhand, maxhand;
double rdns;
int dxmin, dymin, dxmax, dymax;
double radins, sine, cosine;
double fminutes;
Thread t = null;
Boolean stopFlag;

22
public void start() {
t = new Thread(this);
stopFlag = false;
t.start();
}
public void run() {
for (;;) {
try {
updateTime();
repaint();
Thread.sleep(1000);
if (stopFlag)
break;
} catch (InterruptedException e) {
}
}
}
public void stop() {
stopFlag = true;
t = null;
}
private void updateTime() {
nw.setTimeInMillis(System.currentTimeMillis());
}

23
g.setFont(new Font("Gabriola", Font.BOLD + Font.ITALIC, 160));
g.setColor(Color.RED);
g.drawString("XUS", 300, 270);
g.setFont(new Font("Consolas", Font.BOLD + Font.ITALIC, 100));
g.setColor(Color.GREEN);
g.drawString("20", 550, 270);
g.setColor(Color.black);
g.fillOval(100, 100, 200, 200);
Graphics2D g1 = (Graphics2D) g;
int hours = nw.get(Calendar.HOUR);
int minutes = nw.get(Calendar.MINUTE);
int seconds = nw.get(Calendar.SECOND);
int millis = nw.get(Calendar.MILLISECOND);
minhand = width / 8;
maxhand = width / 2;
rdns = (seconds + ((double) millis / 1000)) / 60.0;
drw(g1, rdns, 0, maxhand - 20);
g1.setColor(Color.BLUE);
g1.drawString(
String.format("%02d : %02d :%02d ", hours, minutes, seconds),
minhand + 150, maxhand + 170);

24
minhand = 0; // Minute hand starts in middle.
fminutes = (minutes + rdns) / 60.0;
drw(g1, fminutes, 0, maxhand);
minhand = 0; // Minute hand starts in middle.
drw(g1, (hours + fminutes) / 12.0, 0, maxhand);
g1.setColor(Color.gray); // set b ackground of circle
g1.drawOval(100, 100, 200, 200); // draw a circle
g1.setColor(Color.WHITE);
g1.setFont(new Font("Consulas", Font.BOLD + Font.ITALIC, 15));
g1.drawString("12", 190, 120);
g1.drawString("6", 195, 290);
g1.drawString("3", 280, 200);
g1.drawString("6", 110, 200);
g1.setFont(new Font("Consulas", Font.BOLD + Font.ITALIC, 15));
g1.setStroke(new BasicStroke(2, BasicStroke.JOIN_MITER,
BasicStroke.JOIN_BEVEL));
}

End - Analog Clock Example
public void drw(Graphics2D g, double prct, int minRadius, int maxRadius) {
radins = (0.5 - prct) * TWO_PI;
sine = Math.sin(radins);
cosine = Math.cos(radins);
dxmin = xcent + (int) (minRadius * sine);
dymin = ycent + (int) (minRadius * cosine);
dxmax = xcent + (int) (maxRadius * sine);
dymax = ycent + (int) (maxRadius * cosine);
g.setColor(Color.WHITE);
g.setBackground(Color.cyan);
g.setFont(new Font("Consulas", Font.BOLD + Font.ITALIC, 12));
g.drawLine(dxmin + 100, dymin + 100, dxmax + 100, dymax + 100);
}
}
25

OUTPUT - Analog Clock Example
26

END
27

Java Applet and Graphics

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