tutorial-ccsc-mw2009

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The ACM Java Libraries

Andrew Mertz William Slough Nancy Van Cleave

Mathematics and Computer Science Department Eastern Illinois University

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Introduction

NetBeans and Java

The ACM Java Task Force (JTF) Libraries

Placing applets on web pages

How to learn about the ACM libraries: This workshop

Textbooks

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ACM library galleries

EIU student work:

http://www.eiu.edu/~mathcs/http

JTF demo gallery:

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Installing the necessary software:

NetBeans

www.netbeans.org/downloads/

Click on theDownload NetBeans IDE Button

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Installating the necessary software: ACM Java libraries

jtf.acm.org— obtainacm.zip Create acmLibraryproject in NetBeans

File →New Project

Within theCategoriespanel, selectJava

Within theProjects, selectJava Class Library

ClickNextto proceed

For the project name, enteracmLibrary

Click on theFinishbutton

Move the acm.zip file to theacmLibrary/srcdirectory

Unpack the zip file (into the acmLibrary/src directory)

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The

Program

class diagram

JApplet

Program

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A “Hello, world!” program

Create HelloProgram project File →New Project

Within theCategoriespanel, selectJava

Within theProjects, selectJava Class Library

ClickNextto proceed

For the project name, enterHelloProgram

Click on theFinishbutton

Make the acmLibraryavailable to this project Right–click onLibraries, selectAdd Project

In theAdd Projectwindow chooseacmLibrary

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Create a new Java program

Right–click onSource Packages, then select New→ Other

SelectJava from the categories

The file type to select is Empty Java File

ClickNext, then replace the suggested class name NewEmpty

with HelloProgram

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A “Hello, world!” program: in a console window

import acm.graphics.*; import acm.program.*;

public class HelloProgram extends ConsoleProgram { public void run() {

println("Hello, world!"); }

}

Modifications:

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A “Hello, world!” program: with dialog boxes

public class HelloProgram extends DialogProgram { public void run() {

println("Hello, world!"); println("Name here");

println("Organization here"); }

}

Modifications:

ChangeConsoleProgram to DialogProgram

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A “Hello, world!” program: in a graphics window

public class HelloProgram extends GraphicsProgram { public void run() {

add(new GLabel("Hello, world!", 100, 75)); }

}

Modifications:

Move the output line down

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Placing applets on a web site

index.html

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Add2Quantities

import acm.program.*;

public class Add2Quantities extends ConsoleProgram { public void run() {

println("This program adds two values:"); int a = readInt("Enter a: ");

int b = readInt("Enter b: "); int sum = a + b;

println("The sum is " + sum + "."); }

}

Modifications:

Convert to a DialogProgram

Different data types:

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The

acm.graphics

model

Theacm.graphicspackage uses acollage model in which you create an image by adding various objects to a canvas.

This is similar to a felt board that serves as a backdrop for colored shapes that stick to the felt surface.

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The Java coordinate system

All distances and coordinates in the graphics library are measured inpixels.

Coordinates in the graphics model are specified relative to the originin the upper left corner of the screen.

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Partial class diagram for

acm.graphics

java.awt.Container

GCanvas GObject GCompound

GLabel GRect

GOval

GLine

GPolygon

GImage

GArc

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The

GCanvas

class

TheGCanvasclass represents the background canvas, a virtual felt board.

When you use theacm.graphics package, you create pictures by adding variousGObjectsto a GCanvas.

For simple applications, you will not need to work with an explicit

GCanvasobject.

Programs that extendGraphicsProgram, automatically creates a

GCanvasand resizes it so that it fills the program window.

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Methods in the GCanvas class

add(object) Adds the object to the canvas at the front of the stack

add(object, x, y) Moves the object to (x, y) and then adds it to the canvas

remove(object) Removes the object from the canvas

removeAll() Removes all objects from the canvas

getElementAt(x, y) Returns the front most object at (x, y), or null if none

getWidth() Returns the width in pixels of the canvas

getHeight() Returns the height in pixels of the canvas

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Methods in the

GCanvas

class

The following methods are available in GraphicsProgram only: pause(milliseconds) Pauses the program for the specified time

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Two forms of the

add

method

The add method comes in two forms. add(object);

adds the object at the location currently stored in its internal structure. You use this form when you have already set the coordinates of the object, usually done when it was created. The second form:

add(object, x, y);

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Centering text

public class CenteredLabel extends GraphicsProgram {

public void run() {

GLabel label = new GLabel("I am centered"); add(label,

(getWidth() - label.getWidth()) / 2, (getHeight() - label.getHeight()) / 2); }

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Methods common to

GObject

s

setLocation(x, y) Resets the location of the object to the specified point

move(dx, dy) Moves the objectdxanddypixels

movePolar(r, theta) Moves the objectrpixels in the directiontheta

getX() Returns thexcoordinate of the object

getY() Returns theycoordinate of the object

getWidth() Returns the horizontal width of the object in pixels

getHeight() Returns the vertical height of the object in pixels

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Methods common to

GObject

s (continued)

setColor(c) Sets the color of the object

getColor() Returns the color currently assigned to the object

setVisible(flag) Sets visibility (false= invisible,true= visible)

isVisible() Returnstrueif the object is visible

sendToFront() Sends the object to the front of the stacking order

sendToBack() Sends the object to the back of the stacking order

sendForward() Sends the object forward one position in the stack-ing order

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Sharing behavior through interfaces

There are some methods that apply to someGObject subclasses, but not others.

For example, you can callsetFilled onGOvals orGRects. However, it does not make sense to callsetFilledon a GLine.

In theacm.graphics package, there are three interfaces that define methods for certainGObject subclasses:

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acm.graphics

interfaces

GFillable(GArc,GOval,GPolygon,GRect)

setFilled(flag) Sets the fill state (false= outlined,true= filled)

isFilled() Returns the fill state

setFillColor(c) Sets the color used to fill the interior

getFillColor() Returns the fill color

GResizable(GImage,GOval,GRect)

setSize(width, height) Sets the dimensions of the object

setBounds(x, y, width, height) Sets the location and dimensions

GScalable(GArc,GCompound,GLine,GImage,GOval,GPolygon,GRect) scale(sf) Scales both dimensions of the object bysf

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Encapsulated coordinates

Theacm.graphicspackage defines three classes:

GPoint GDimension GRectangle

These combine geometric information about coordinates and sizes into a single object.

GPoint encapsulates the x andy coordinates of a point

GDimension encapsulates width and height values that specify an object’s size

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Gathering input

Event driven model

Most of the time the program is waiting for something (anevent) to occur

When an event occurs, the program responds appropriately

event Respond to

an event

Event occurs Response

complete

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The Java event model

In Java, you indicate what events you wish to respond to by designating some object as alistenerfor that event.

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Events the ACM library facilitates

Keyboard events: key presses and key releases. Identifies the key and whether shift, control and/or alt are also pressed.

Mouse events: motion, button presses and button releases. Motion events tell where the position of the mouse is now, how far it moved and if any buttons are pressed.

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A simple event-driven program

import acm.graphics.*; import acm.program.*; import java.awt.event.*;

public class Dots extends GraphicsProgram { public void init() {

addMouseListeners(); }

public void mouseClicked(MouseEvent e) { GOval dot = new GOval(DOT_SIZE, DOT_SIZE); dot.setFilled(true);

add(dot,

e.getX() - DOT_SIZE/2, e.getY() - DOT_SIZE/2); }

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How it works

TheaddMouseListenersmethod of acm.program.Program

enables mouse-event reporting.

Clicking the mouse generates aMouseEvent.

That event triggers a call to themouseClicked method.

The program responds by adding a newGOvalto the canvas.

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acm.util.RandomGenerator

TheRandomGeneratorclass can generate pseudorandom integers, doubles, booleans, and colors.

Methods provided include:

nextBoolean(double p) Returns a random boolean value with the specified probability

nextColor() Returns a random opaque Color

nextDouble(double low, double high) Returns a random real number in the specified range

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The

GMath

class

TheGMathclass has the following static methods:

sinDegrees(theta) Returns the sine oftheta, measured in degrees

cosDegrees(theta) Returns the cosine oftheta

tanDegrees(theta) Returns the tangent oftheta

toRadians(degrees) Converts an angle from degrees to radians

toDegrees(radians) Converts an angle from radians to degrees

distance(x, y) Returns the distance from the origin to(x, y)

distance(x0, y0, x1, y1) Returns the distance from(x0, y0)to(x1, y1)

round(x) Returns the closest int tox

angle(x, y) Returns the angle in degrees formed by the line connecting the origin to the point(x, y)

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Adding a touch of color

public class Dots extends GraphicsProgram { public void init() {

public void mouseClicked(MouseEvent e) { GOval dot = new GOval(DOT_SIZE, DOT_SIZE); dot.setFilled(true);

dot.setColor(rand.nextColor()); add(dot,

e.getX() - DOT_SIZE/2, e.getY() - DOT_SIZE/2); }

private static final double DOT_SIZE = 20; private static RandomGenerator rand =

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Responding to mouse events

1. Define an init method that callsaddMouseListeners. 2. Write new definitions of any listener methods you need. The most common mouse events and associated listener methods:

Method When invoked

mouseClicked(e) when the user clicks the mouse

mousePressed(e) when the mouse button is pressed

mouseReleased(e) when the mouse button is released

mouseMoved(e) when the user moves the mouse

mouseDragged(e) when the mouse is dragged with the button down

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Lines

public class Lines extends GraphicsProgram { private GPoint lastPoint;

public void init() {

lastPoint = new GPoint(getWidth()/2,getHeight()/2); addMouseListeners();

}

public void mouseClicked(MouseEvent e){

add(new GLine(lastPoint.getX(), lastPoint.getY(), e.getX(), e.getY()));

lastPoint.setLocation(e.getX(), e.getY()); }

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DragLines

public class DragLines extends GraphicsProgram { public void init() {

public void mousePressed(MouseEvent e) { line = new GLine(e.getX(), e.getY(),

e.getX(), e.getY()); add(line);

}

public void mouseDragged(MouseEvent e) { line.setEndPoint(e.getX(), e.getY()); }

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Exercise: Dragging dots

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DragObjects

public class DragObjects extends GraphicsProgram { public void init() {

GRect rect = new GRect(100, 100, 150, 100); rect.setFilled(true);

rect.setColor(Color.RED); add(rect);

GOval oval = new GOval(300, 115, 100, 70); oval.setFilled(true);

oval.setColor(Color.GREEN); add(oval);

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DragObjects

public void mouseDragged(MouseEvent e) { if(gobj != null){

gobj.move(e.getX() - last.getX(), e.getY() - last.getY()); last = new GPoint(e.getPoint()); }

}

public void mouseClicked(MouseEvent e) { if (gobj != null) gobj.sendToFront(); }

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Mouse listeners

The ACM Java Libraries simplifies the JFC approach to mouse listeners.

To maximize efficiency, Java defines two distinct listener interfaces.

TheMouseListenerinterface responds to mouse events that happen relatively infrequently, such as clicking the mouse button.

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GImage

The ACM Library makes displaying images very easy and you can still use all of the other features of Swing.

import acm.graphics.*; import acm.program.*; import javax.swing.*;

public class ShowPicture extends GraphicsProgram {

public void run() {

JFileChooser chooser = new JFileChooser(); chooser.showOpenDialog(null);

String filename = chooser.getSelectedFile().getPath(); GImage image = new GImage(filename);

setSize((int) image.getWidth(), (int) image.getHeight()); add(image);

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Animation

Thepausemethod allows for simple animations.

double windowWidth = getWidth(); double windowHeight = getHeight();

// calculate ball size and steps double size = 0.06 * windowWidth; double dx = size / 8.0;

double dy = size / 8.0;

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Animation

GOval ball = new GOval(windowWidth/2.0,

windowHeight/2.0, size, size); ball.setColor(Color.RED);

ball.setFilled(true); ball.setFillColor(Color.ORANGE); add(ball);

int count = 0;

while (count < BOUNCES) {

if ((ball.getX() + size > windowWidth) || (ball.getX() <= 0.0)) {

dx = -dx; count++; }

if ((ball.getY() + size > windowHeight) || (ball.getY() <= 0.0)) {

dy = -dy; count++; }

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Animation

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GPolygon

TheGPolygonclass can be used to represent closed polygonal shapes.

Initially, aGPolygon has no vertices. Vertices are added via the following methods:

addArc(arcWidth, arcHeight, start, sweep)

Adds a series of edges to simulate an arc

addEdge(dx, dy) Adds an edge using the given dis-placement from the last vertex

addPolarEdge(r, theta) Adds an edge using the given polar coordinates

addVertex(x, y) Adds a vertex relative to the polygon origin

The coordinates of vertices are expressed with respect to the origin of the polygon (its location on a canvas).

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Drawing a diamond

public class Diamond extends GraphicsProgram {

public void run() {

GPolygon diamond = new GPolygon(); diamond.addVertex(-30, 0);

diamond.addVertex(0, 40); diamond.addVertex(30, 0); diamond.addVertex(0, -40); diamond.setFilled(true);

diamond.setFillColor(Color.BLUE);

add(diamond, getWidth()/2, getHeight()/2); }

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Exercise: Diamonds

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GCompound

GCompoundobjects are like canvases, you can add otherGObjects to them.

Some ofGCompound’s methods:

add(gobj) Adds an object to thisGCompound

add(gobj, x, y) Adds an object at the point (x, y)

markAsComplete() Makes it illegal to add or remove elements

remove(gobj) Removes an object

removeAll() Removes all objects

The coordinates of vertices are expressed with respect to the origin of the compound object (its location on a canvas).

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Turtles

TheGTurtleclass enables graphics using a LOGO-like model of a turtle moving across the screen leaving a trail.

forward(distance) Moves the turtle forward

hideTurtle() Hides the turtle

left(angle) Turns the specified number of degrees to the left

penDown() Lowers the pen

penUp() Raises the pen

right(angle) Turns the specified number of degrees to the left

setDirection(dir) Sets the direction in which the turtle is moving

setLocation(x, y) Moves to the point (x, y) without drawing a line

setSpeed(speed) Sets the speed of the turtle, 0 (slowest) and 1 (fastest)

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Fractals

GTurtlecan be very useful for many types of graphics, especially fractals.

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Snowflakes

public class Koch_1 extends GraphicsProgram {

private GTurtle turtle = new GTurtle(); private int order = 4;

private double length = 300;

public void init() { setSize(600, 600);

add(turtle, (getWidth() - length) / 2, (getHeight() - length) / 2); turtle.setSpeed(0.8);

turtle.penDown(); }

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Snowflakes

private void zig(int order, double length) { if (order == 0) turtle.forward(length); else {

zig(order - 1, length / 3.0); turtle.left(60);

zig(order - 1, length / 3.0); turtle.right(120);

zig(order - 1, length / 3.0); turtle.left(60);

zig(order - 1, length / 3.0); }

}

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Snowflakes

public void run() { zig(order, length); turtle.right(120); zig(order, length); turtle.right(120); zig(order, length); turtle.right(120); }

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Exercise: Fractal

Make another fractal where the order 0 case is a square and the orderncase replaces each line of the order n−1 case with the following:

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