The ACM Java Libraries

Andrew Mertz William Slough Nancy Van Cleave

Mathematics and Computer Science Department Eastern Illinois University

October 10, 2009

CCSC:MW 2009, Saint Xavier University 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 ACM Java Task Force Tutorial Javadoc documentation

CCSC:MW 2009, Saint Xavier University Textbook support for ACM libraries

CCSC:MW 2009, Saint Xavier University ACM library galleries

EIU student work: http://www.eiu.edu/~mathcs/http

JTF demo gallery: http://jtf.acm.org/demos/index.html

CCSC:MW 2009, Saint Xavier University Installing the necessary software: NetBeans

www.netbeans.org/downloads/

Click on the Download NetBeans IDE Button

Run install

CCSC:MW 2009, Saint Xavier University Installating the necessary software: ACM Java libraries

jtf.acm.org — obtain acm.zip

Create acmLibrary project in NetBeans File → New Project Within the Categories panel, select Java Within the Projects, select Java Class Library Click Next to proceed For the project name, enter acmLibrary Click on the Finish button

Move the acm.zip ﬁle to the acmLibrary/src directory

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

Right–click on the acmLibrary project in NetBeans, and select close (don’t shut down NetBeans)

CCSC:MW 2009, Saint Xavier University The Program class diagram

JApplet

Program

GraphicsProgram ConsoleProgram DialogProgram

CCSC:MW 2009, Saint Xavier University A “Hello, world!” program

Create HelloProgram project File → New Project Within the Categories panel, select Java Within the Projects, select Java Class Library Click Next to proceed For the project name, enter HelloProgram Click on the Finish button

Make the acmLibrary available to this project Right–click on Libraries, select Add Project In the Add Project window choose acmLibrary Click on Add Project / Jar ﬁles

CCSC:MW 2009, Saint Xavier University Create a new Java program

Right–click on Source Packages, then select New → Other

Select Java from the categories

The ﬁle type to select is Empty Java File

Click Next, then replace the suggested class name NewEmpty with HelloProgram

Click the Finish button

CCSC:MW 2009, Saint Xavier University 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: Add a second line below the ﬁrst with your name Add a third line with your organization

CCSC:MW 2009, Saint Xavier University A “Hello, world!” program: with dialog boxes

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

public class HelloProgram extends DialogProgram { public void run() { println("Hello, world!"); println("Name here"); println("Organization here"); } }

Modiﬁcations: Change ConsoleProgram to DialogProgram Change ﬁrst two println statements to print statements with \n to produce a single dialog window

CCSC:MW 2009, Saint Xavier University A “Hello, world!” program: in a graphics window

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

public class HelloProgram extends GraphicsProgram { public void run() { add(new GLabel("Hello, world!", 100, 75)); } }

Modiﬁcations: Move the output line down Add lines for your name and organization

CCSC:MW 2009, Saint Xavier University Placing applets on a web site

index.html

HelloProgram.html

CCSC:MW 2009, Saint Xavier University 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: int → double, readInt → readDouble int → String, readInt → readLine

CCSC:MW 2009, Saint Xavier University The acm.graphics model

The acm.graphics package uses a collage 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.

Note that newer objects can obscure those added earlier. This layering arrangement is called the stacking order or z-order.

CCSC:MW 2009, Saint Xavier University The Java coordinate system

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

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

Coordinate values are speciﬁed as a pair of ﬂoating-point values (x, y) where the values for x increase as you move rightward across the screen and the values for y increase as you move downward.

CCSC:MW 2009, Saint Xavier University Partial class diagram for acm.graphics

GRect GOval GLabel GLine java.awt.Container

GObject GCompound

GPolygon GCanvas GTurtle GImage GArc

CCSC:MW 2009, Saint Xavier University The GCanvas class

The GCanvas class represents the background canvas, a virtual felt board.

When you use the acm.graphics package, you create pictures by adding various GObjects to a GCanvas.

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

Programs that extend GraphicsProgram, automatically creates a GCanvas and resizes it so that it ﬁlls the program window.

Most of the methods deﬁned for the GCanvas class are also available in a GraphicsProgram, thanks to delegation.

CCSC:MW 2009, Saint Xavier University 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 setBackground(c) Sets the background color of the canvas

CCSC:MW 2009, Saint Xavier University Methods in the GCanvas class

The following methods are available in GraphicsProgram only:

pause(milliseconds) Pauses the program for the speciﬁed time waitForClick() Suspends the program until the user clicks the mouse

CCSC:MW 2009, Saint Xavier University 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);

which moves the object to the point (x, y) and then adds it there. This form is useful when you need to determine some property of the object before you know where to put it. If, for example, you want to center a GLabel, you must ﬁrst create it and then use its size to determine its location.

CCSC:MW 2009, Saint Xavier University Centering text

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

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); } }

CCSC:MW 2009, Saint Xavier University Methods common to GObjects

setLocation(x, y) Resets the location of the object to the speciﬁed point move(dx, dy) Moves the object dx and dy pixels movePolar(r, theta) Moves the object r pixels in the direction theta getX() Returns the x coordinate of the object getY() Returns the y coordinate of the object getWidth() Returns the horizontal width of the object in pixels getHeight() Returns the vertical height of the object in pixels contains(x, y) Returns true if the object contains the speciﬁed point

CCSC:MW 2009, Saint Xavier University Methods common to GObjects (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() Returns true if 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 stacking order sendBackward() Sends the object backward one position in the stacking order

CCSC:MW 2009, Saint Xavier University Sharing behavior through interfaces

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

For example, you can call setFilled on GOvals or GRects. However, it does not make sense to call setFilled on a GLine.

In the acm.graphics package, there are three interfaces that deﬁne methods for certain GObject subclasses: GFillable GResizable GScalable

CCSC:MW 2009, Saint Xavier University 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 by sf scale(sx, sy) Scales the object by sx horizontally and sy vertically

CCSC:MW 2009, Saint Xavier University Making a face

CCSC:MW 2009, Saint Xavier University Exercise: Drawing a house

CCSC:MW 2009, Saint Xavier University Encapsulated coordinates

The acm.graphics package deﬁnes three classes: GPoint GDimension GRectangle These combine geometric information about coordinates and sizes into a single object.

GPoint encapsulates the x and y coordinates of a point GDimension encapsulates width and height values that specify an object’s size GRectangle encapsulates all four of these values by specifying both the origin and size of a rectangle

CCSC:MW 2009, Saint Xavier University Gathering input

Event driven model Most of the time the program is waiting for something (an event) to occur When an event occurs, the program responds appropriately

Wait for an event

Response complete Event occurs

Respond to event

CCSC:MW 2009, Saint Xavier University The Java event model

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

When the event occurs, a message is sent to the listener, which triggers the appropriate response.

CCSC:MW 2009, Saint Xavier University 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.

Action events: GUI buttons pressed and other user-interface actions.

CCSC:MW 2009, Saint Xavier University 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); } private static final double DOT_SIZE = 20; }

CCSC:MW 2009, Saint Xavier University How it works

The addMouseListeners method of acm.program.Program enables mouse-event reporting.

Clicking the mouse generates a MouseEvent.

That event triggers a call to the mouseClicked method.

The program responds by adding a new GOval to the canvas.

Subsequent mouse clicks are treated in exactly the same way.

CCSC:MW 2009, Saint Xavier University acm.util.RandomGenerator

The RandomGenerator class 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 nextInt(int low, int high) Returns a random integer in the specified range

CCSC:MW 2009, Saint Xavier University The GMath class

The GMath class has the following static methods:

sinDegrees(theta) Returns the sine of theta, measured in degrees cosDegrees(theta) Returns the cosine of theta tanDegrees(theta) Returns the tangent of theta 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 to x angle(x, y) Returns the angle in degrees formed by the line connecting the origin to the point (x, y) angle(x0, y0, x1, y1) Returns the angle in degrees formed by the line connecting the points (x0, y0) and (x1, y1)

CCSC:MW 2009, Saint Xavier University Adding a touch of color

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); 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 = new RandomGenerator(); }

CCSC:MW 2009, Saint Xavier University Responding to mouse events

1. Deﬁne an init method that calls addMouseListeners. 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

The parameter e is a MouseEvent object, which provides more data about the event, such as the location of the mouse.

CCSC:MW 2009, Saint Xavier University 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()); } }

CCSC:MW 2009, Saint Xavier University DragLines

public class DragLines extends GraphicsProgram { public void init() { addMouseListeners(); }

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()); }

private GLine line; }

CCSC:MW 2009, Saint Xavier University Exercise: Dragging dots

Write a program that displays randomly colored dots whose size is based on the amount the mouse is dragged.

CCSC:MW 2009, Saint Xavier University 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); addMouseListeners(); }

public void mousePressed(MouseEvent e) { last = new GPoint(e.getPoint()); gobj = getElementAt(last); }

. . . continues on next slide CCSC:MW 2009, Saint Xavier University 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(); }

private GObject gobj; /* The object being dragged */ private GPoint last; /* The last mouse position */ }

CCSC:MW 2009, Saint Xavier University Mouse listeners

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

To maximize eﬃciency, Java deﬁnes two distinct listener interfaces.

The MouseListener interface responds to mouse events that happen relatively infrequently, such as clicking the mouse button.

The MouseMotionListener interface responds to the much more rapid-ﬁre events that occur when you move or drag the mouse.

CCSC:MW 2009, Saint Xavier University 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); } }

CCSC:MW 2009, Saint Xavier University Animation

The pause method 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;

. . . continues on next slide

CCSC:MW 2009, Saint Xavier University 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++; } ball.move(dx, dy); pause(PAUSE_TIME); }

CCSC:MW 2009, Saint Xavier University Animation

Modify the bouncing ball demo to bounce an image around the screen.

CCSC:MW 2009, Saint Xavier University GPolygon

The GPolygon class can be used to represent closed polygonal shapes. Initially, a GPolygon has no vertices. Vertices are added via the following methods:

addArc(arcWidth, arcHeight, Adds a series of edges to simulate start, sweep) 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). GPolygons are resizable.

CCSC:MW 2009, Saint Xavier University 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); } }

CCSC:MW 2009, Saint Xavier University Exercise: Diamonds

Create a program that draws randomly sized and colored diamonds where clicked.

CCSC:MW 2009, Saint Xavier University GCompound

GCompound objects are like canvases, you can add other GObjects to them. Some of GCompound’s methods:

add(gobj) Adds an object to this GCompound 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).

GCompound objects are resizable.

CCSC:MW 2009, Saint Xavier University Make a face as a compound object

CCSC:MW 2009, Saint Xavier University Exercise: Draw a house as a compound object

CCSC:MW 2009, Saint Xavier University Turtles

The GTurtle class 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) showTurtle() Makes the turtle visible

CCSC:MW 2009, Saint Xavier University Fractals

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

The order 0 Koch snowflake is an equilateral triangle. The order n Koch snowflake replaces each line of the order n − 1 snowflake with the following:

CCSC:MW 2009, Saint Xavier University Fractals

CCSC:MW 2009, Saint Xavier University 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(); } . . . continues on next slide

CCSC:MW 2009, Saint Xavier University 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); } } . . . continues on next slide

CCSC:MW 2009, Saint Xavier University Snowﬂakes

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

CCSC:MW 2009, Saint Xavier University Exercise: Fractal

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

Note that there are 8 segments in the production rule.

CCSC:MW 2009, Saint Xavier University Fractals

CCSC:MW 2009, Saint Xavier University