eScience Lectures Notes : Introduction to Java and Java 2D

Slide 1 : Introduction to Java 2D

Introduction to Java 2D

Java Revisal

I will try to go trough quite quickly on that first part as it should be a revisal for most of view. If something is not clear, it is time to ask question now...

Java Specifics : space and curly braces

Java 2D

First look at the example : ShapesDemo2D.java

Stroking and Filling Graphics Primitives

Second look at the example : ShapesDemo2D.java

Object-Oriented Programming

A bit of ad : OOP ask a effort in the begining...

Java supports the Object-Oriented Programming (OOP) approach.

OOP focuses on the design of data-types (called objects or classes) rather than algorithms

Why is this distinction important?

Objects are nouns, Algorithms are verbs

If you want to put a windows in a wall, you don't say :

"Let's use a hamer to make a hole in that wall, then let's mesure the size of the hole, then lets buy some piece of wood that we will put together, then...

You say : Let's decide to have a windows in that wall

You know first what you want and then you think of the way you will get it

Which is an easier task?

identify the actions that apply to a given noun
identify those objects to which a given action might be applied
Exemple : Verb "to buy" / Object "Car"

isn'it easier to list the actions that you can do with a car (to buy, to sell, ...to drive°) than to list all the object you can buy ... and forget lots of them ?

What is easier?

identifying similar object classes

is a relationship

specifying general-purpose algorithms

with lots of "if then else" statements

Advantages of OOP

promotes design abstraction (hiding details)
promotes code reuse
consolidates specification and interface ... encapsulation

Slide 3 : CG Example

CG Example

Object-Oriented Design	Procedural Design
Similar object classes Common interfaces Common usage Code reuse-- inheritance Defers implementation and algorithm decisions From general architecture towards details	Algorithm centered-- forces early implementation and algorithm decisions Exposes more details Difficult to extend Difficult to maintain From details towards construction of complex buildings

Object-Oriented Design

Procedural Design

Similar object classes
Common interfaces
Common usage
Code reuse-- inheritance
Defers implementation and algorithm decisions

From general architecture towards details

Algorithm centered--
forces early implementation
and algorithm decisions
Exposes more details
Difficult to extend
Difficult to maintain

From details towards construction of complex buildings

Slide 4 : Polymorphism

Polymorphism

Polymorphism allows algorithms to be specified in terms of the most general (and/or reasonable) object type


void processShape(Shape s) 
	{
	s.setColor(Color.red);
 	// ... do stuff
	s.draw();
	}
         
Circle c = new Circle(x, y, r);
         
Point2D v1 = new Point2D(x1, y1);
Point2D v2 = new Point2D(x2, y2);
Point2D v3 = new Point2D(x3, y3);
Triangle t = new Triangle(v1, v2, v3);
         
Point2D c1 = new Point2D(u1, v1);
Point2D c2 = new Point2D(u2, v2);
Triangle r = new Rectangle(c1, c2);
         
processShape(c);
processShape(t);
processShape(r);

Slide 5 : Java Specifics

Java Specifics : space and curly braces

A Java source program is composed of white space, comments, declarations, and statements.


{
	White space is a very important part of any Java program    
	{
		has no effect on the code's meaning
		enhances readability and communicates structure

		includes : spaces, tabs, and new lines.
		typically, tabs or indention set off blocks of code
		new-lines separate statements
	}
}

There are lots of differents "rules and conventions" on using white space and curly braces.

Adopt a consistent style !

Make sure that readers could easily find begining and end of your blocks

A Java source program is composed of white space, comments, declarations, and statements.
White space is a very important part of any Java program. While it has no effect on the meaning of the code, white space, more than any other factor, contributes to the readability and signals the structure of a code fragment. White space includes, spaces, tabs, and new lines. Typically, tabs or indention is used to set off blocks of code, and new lines are used to separate statements. There are no hard-fast rules how and when to use white space, all I suggest is that you adopt a consistent style.

Slide 6 : Comments

Comments

Next to white space, the most important parts of any Java program are its comments.

Inline comments:

	answer = 42; // valid independent of the input

Block comments:

/*
... This next bit of code is so obvious that I hesitated    
  to comment it a first. 
  For those whom intergalactic culture is limited,
  please refer to the textbook :  
  "the hitch hicker guide for the galaxy" by Douglas Adams.

  tip : 42 is the answer for life, the universe and everything
*/ 
	answer = 42;

Next to white space, the most important part of any Java program is comments. Keep in mind the syntax of a language is designed for communicating a program's design to a computer. Comments, on the other hand, are the primary mechanism for communicating a program's design to humans. Java has three types of comments.

Slide 7 : Special Comments

Special Comments

Java provides a special form of comment for generating automatic documentation, and web pages. It uses a tool called javadoc. Within these special comment blocks several special variables, indicated by a leading @, are recognized.

Documentation comments:

 
/** The Universe and Everything
 *
 *	@version 0.9999 Date : This must be Thursday
 *	@author Ford Prefect
 *	@author Arthur Dent
 *  @see <A HREF="http://users.milliways.mg-net.de/BSAFH/guide/">the book</A>
 */
 
public class theUnivers 
{
	public static String getTheAnswer()
	{
		return("42");
	}
	
	/**
	 *  @deprecated Rember a imoprtant thing about that question ...
	 * "It is said that if both the question and the answer to Life, 
	 * the Universe and Everything ever exist in the same dimention 
	 * it will dissappear and be replaced by something even more strange 
	 * and unexplicable" -Hitch Hicker Guide To The Galaxy
	 */
	private String getTheQuestion()
	{
	while(true)
		{
		sleep(1);
		}
	}
}

Slide 8 : Java Data Types

Java Data Types

Variables in Java must be objects, arrays, or one of the primitive data types

Java has 8 primitive data types
(boolean, byte, short, int, long, double, float, char)

Notes:

All integer types are signed (and there is no unsigned keyword)
Unlike C and C++ char variables are 16 rather than 8 bits
Because Java is Unicode compliant
Unlike C Type have a definitly fixed size
in C, it used to depent on the compiler
Primitive data types are passed to method by value
the actual value of a primitive type can only be modified by the methods of the declaring or derived object

boolean likeeScience = true;
	/*	boolean likewise have values {true, false}
		they can never be mixed up with integer or other type
	 */
byte teeth = 32;		// bytes go from -128 to 127
if (!likeeScience) teeth = teeth - 1;
float pi = 3.141592f; 	// you need the "f" here
short classes = 0xbad;	// hexadecimal

Slide 9 : Java Arrays

Java Arrays

Java arrays fall between a primitive data type and an object

Properties of Java arrays:

can contain objects, primitive types, or other arrays
contents are accessed via zero-based positive integers enclosed within the brackets, [, and ]
declaration, creation and, value initialisation of arrays are distinct operations
created with the new operator
uninitialized arrays have a value of null
have a single instance variable called 'length'
checks at run time, that all accesses are between 0 and length - 1
passed to methods by reference

byte buffer[];		// array declaration (buffer = null)
buffer = new byte[1024];	// array creation (contents initialized to zeros)
int table[] = new int[10];	// declaration and creation combined
   
int sqrs[] = {0, 1, 4, 9, 16, 25, 36, 49, 64, 81 }; // with an initializer
buffer[5] = sqrs[sqrs.length-1]; // array references
   
int triangle[][] = new int[3][];	// 2D Arrays do not have to be matrix
triangle[0] = new int[3];
triangle[1] = new int[2];
triangle[2] = new int[1];

Slide 10 : Java Objects

Java Objects

Objects are containers around aggregates of primitive types, arrays, and other objects

Properties of Classes
All Java code is contained within objects
Excepted comments, import and package statements.
Objects are passed to methods by reference
Definition, declaration, and creation of objects are distinct
Instances of objects are created with new and have a value of null
Objects have four forms: the class, the abstract class, the inner class, and the interface

class Circle						// object definition
{	static double pi = 3.141592;	// class variable
	double radius;					// instance variable
	public Circle(double r)			// constructor method
	{	radius = r;
	}
	public double circumference()	{	return 2*pi*radius; }
	public double area()	{	return pi*radius*radius; }
	public static getPi()	{	return pi;	}	// class method
}
   
Circle c;				// object declaration
c = new Circle(4.0);	// object creation
double a = c.area();	// object method call

Slide 11 : Java Statements

Java Statements

Statements are all that remains!

Individual statements are terminated by semicolons
Blocks of statements are grouped using braces, {, and }
Simplest statement is the expression.

An expression is a string of variables and constants separated by operators.
Java allows the following set of operators within statements:

. [] ()
++ -- ! ~ instanceof
* / %
+ -
<< >> >>>
< > <= >=
== !=
&
^
|
&&
||
?:
= *= /= %= += -= <<= >>= >>>= &= ^= |=

The final component of a Java program is its statements. Individual statements are terminated by semicolons. Groups of statements and declarations enclosed within braces, { and }, are called block statements and they act like an individual statement. Block statements do not require a terminating semicolon. The simplest type of statement is the expression.

An expression is a string of variables and constants separated by operators. A common type of expression is the assignment where a variable is given the value of the expression to the left of an equal sign. If one of the operator-assignment forms is used, the variable is given the value of expression to the left of the equals sign combined with it previous value of the variable as determined by the operator to the left of the equals sign. For more specific details on operators and the types of arguments that they allow see the textbooks.

Slide 12 : Control Statements

Control Statements

The second type of statement is the control statement.

The following list illustrates some of the control statements available in Java:

Really classical structure, espeacially easy to understand for english speaking programmer.
NB : BoolleanExpression are Boolean Expressions)
Break, continue, Label ...

Loop : be sure to get out of it

if (BooleanExpression) Statement
   
if (BooleanExpression) Statement else Statement
   
while (BooleanExpression) Statement
   
do Statement while (BooleanExpression)
   
for (Expression; BooleanExpression; Expression) Statement
   
break <Label>
   
continue <Label>
   
Label: Statement
   
switch (IntegerExpression)
{
	case IntegerValue:
		Statements
	default:
		Statements
}

return Expression

In these examples reserved keywords are shown in bold.

Slide 13 : Over Java Issue

Over Java Subject

Constructors and the "new" operator

new create a new objet from a class. It allocates memory and call the adequate constructor method of the class to initialize field values.

Class variables and method distinctions
(this, super, abstract, final, static, instance, and class variables)

Let the student talks...
This : the object instance of a class (constructors)
super : the parent class

final : method can't be overwrited (overriden), class can not be subclassed
static : a class thing. No object instance is needed.

Packages (package and import)

This week exercice

Class protection (public, private, protected)

public : accessible anywhere
private : member accessible only within the class that defines it
protected : member accessible only within package and within subclasses.

Exception handling

A way to deal with things that should not happen (better than the if then else)
Each time there is an input from outside of the program

Interfaces and abstract classes

abstract : a method implementation is missing somewhere

We now know enough to write a simple example.

Slide 14 : What you will need...

What you will need...

A text Editor

Mac

BBEdit, ProjectBuilder

Unix

vi, emacs, Xemacs

Windows

TextEdit, Xemacs, TexPad

Java Documentation API :

Locale : http://ephebe.anu.edu.au/doc/index.html

Originale : http://java.sun.com/products/jdk/1.2/download-docs.html

Java Compiler : javac

Java Virtual machine : java

Java comment extractor : javadoc

Java archive tool : jar

and sometime an aplet viewer

and a account to the lab ?

Slide 15 : A First Example

A First Example

Source : HelloWordSimple.java


/** Simple Java 2D Example
 *
 *	@version 0.9  12/07/2001
 *	@author Pascal Vuylsteker
 */
 

import javax.swing.*;
 

public class HelloWordSimple
{	public static void main(String[] args)
	{	HelloWordFrame frame = new HelloWordFrame();
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.show();
	}
}


class HelloWordFrame extends JFrame 
{	public HelloWordFrame()
	{	setTitle("Hello World !! ");
		setSize(300,200);
		
		HelloPanel panel = new HelloPanel();
		Container contentPane = getContentPane();
		contentPane.add(panel);
	}
}

class HelloPanel extends JPanel
{	public void paintComponent(Graphics g)
	{	super.paintComponent(g);
		g.drawString("Hello again...", 20, 20);
	}
}

With some more comments...and notes about JFrame

Slide 16 : A First Example

A First Example

Source : HelloWordSimple.java

All Java source code files should end with a .java extension. When a Java program is compiled one or more .class files are generated. The number of .class files generated by a compile depends on how many objects are defined in the source file.

Let's test it first


/** Simple Java 2D Example
 *
 *	@version 0.9  12/07/2001
 *	@author Pascal Vuylsteker
 */
 

// to tell to the compiler where to look for class definition
// class that are not in the default package nor in java.lang
import javax.swing.*;

// that was missing...
import java.awt.*;


//Since all Java code must be contained within an object, 
// an object called HelloWordSimple is defined in this file.

// "There should be only one"... public class per file

public class HelloWordSimple
{	
//	in order to run a program, the public class should contain 
//  a main method which is static
	public static void main(String[] args)
	{	HelloWordFrame frame = new HelloWordFrame();
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.show();
	}
}

// You don't even need to know any of the details of how a class works, 
//  beyond the interfaces to methods, in order to modify the original code. This 
//  is a simple example of the power of object-oriented programming. 
class HelloWordFrame extends JFrame 
{	public HelloWordFrame()
	{	setTitle("Hello World !! ");
		setSize(300,200);
		
		HelloPanel panel = new HelloPanel();
		Container contentPane = getContentPane();
		contentPane.add(panel);
	}
}

// JPanel has to be extented : the main method contain all
// the work.
class HelloPanel extends JPanel
{	public void paintComponent(Graphics g)
	{	super.paintComponent(g);
		g.drawString("Hello again...", 20, 20);
	}
}

NB : what is wrong with HelloWordSimple2.java ?

It is not object oriented programming...

See the last semester summary about graphics

Slide 17 : JFrame

JFrame

`JFrame` class is a Swing extension of the AWT `Frame` class (Swing adds a J).

It is one of the few ``non-painted'' graphics components.

Frames are examples of containers and we will study ways of inserting graphics objects into them.

Swing lives in `javax.swing.*`.

The 'x' stands for 'extension'.

setSize

By default JFrame has 0x0 pixels! You need to define your own frame class which extends it and which is bigger. Use the setSize() method to increase its size.
Units of size are pixels.

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

defines what happens when you close the frame

In other programs you would want to change this so that the program did not exit whenever the user closed a window. By default a frame is ``hidden'' when a user closes it but the program does not terminate.

show

Frames start their life invisible! You must call show to display them.
Note that the main program exits after the show call.
This just terminates the main thread.
Graphics is in a separate thread.

What else to do ?

Many of the useful JFrame methods are inherited from other classes further up the hierarchy

javax.swing
Class JFrame

java.lang.Object
  |
  +--java.awt.Component
        |
        +--java.awt.Container
              |
              +--java.awt.Window
                    |
                    +--java.awt.Frame
                          |
                          +--javax.swing.JFrame

`Frame` class

dispose
which closes the window down and reclaims any system resources.
setIconImage
which lets you read in your own image for a window icon.
setTitle
setResizable
which takes a boolean argument to specify whether or not the user is able to resize the window.

Component and Window classes
(particularly methods to resize and position the frame):

```
setLocation(x,y)
```

This method can move the frame around. Note that y measures the number of pixels down from the top left corner of the screen. Also note that both arguments are integers.

setBounds(x, y, width, height)
This allows you to define the position and size in one command.

Note that the coordinates in JFrame methods are with respect to the whole screen. In other swing classes they are usually with respect to a specific container.

How to get Screen Dimension ?

It is possible to get the dimensions of the screen you are using by creating an object of class Toolkit and calling its getScreenSize() method. This returns the width and height as fields in a dimension object. The pattern is


        Toolkit kit = Toolkit.getDefaultToolkit();
        Dimension screenSize = kit.getScreenSize();

        int screenHeight = screenSize.height;
        int screenWidth = screenSize.width;

Slide 18 : JPanel

JPanel

Why not on JFrame ?

Added to the JFrame content Pane

The glass pane

Hidden, by default. If you make the glass pane visible, then it's like a sheet of glass over all the other parts of the root pane. It's completely transparent unless you implement the glass pane's paint method so that it does something, and it intercepts input events for the root pane. In the next section, you'll see an example of using a glass pane.

The layered pane

Serves to position its contents, which consist of the content pane and the optional menu bar. Can also hold other components in a specified Z order. For information, see The Layered Pane.

The content pane

The container of the root pane's visible components, excluding the menu bar. For information on using the content pane, see Using Top-Level Containers.

The optional menu bar

The home for the root pane's container's menus. If the container has a menu bar, you generally use the container's setJMenuBar method to put the menu bar in the appropriate place. For more information on using menus and menu bars, see How to Use Menus.

Although it is possible to draw directly onto a JFrame this is considered to be bad programming practice. The thing most swing programmers do is to add components to the content pane which is part of the JFrame. (See fig 7-7.) The thing to do is to call the getContentPane() method of your JFrame to create a Container object and then to add Components to this.

        Container contentPane = getContentPane();
        HelloPanel panel = new HelloPanel();
        contentPane.add(panel);

A panel that extend JPanel :

surfaces onto which you can draw
containers into which you can insert other interface components (sliders, radio buttons.........)

Why do you extend JPanel? Because the basic panel is very boring. You need to override its paintComponent method so that the system will draw interesting objects.

A `paintComponent` method to override

paintComponent is automatically called by the operating system ``when it is needed''. You never call it yourself.
It takes a single argument of type Graphics which remembers the current settings of your graphics such as font and colour. It also has methods to draw patterns, images and text.

The following method

        g.drawString("Hello World!", MESSAGE_X, MESSAGE_Y);

will draw a string at the specified position.

You also need to paint the panel itself and fill it with a background color
```
        super.paintComponent(g);
```

Slide 19 : Java2D Overview

Java2D Overview

Draw lines of any thickness
Fill shapes with gradients and textures
Move, rotate, scale, and shear text and graphics
Composite overlapping text and graphics

For example, you could use the Java 2D API to display complex charts and graphs that use various line and fill styles to distinguish sets of data, like those shown in the following figure.

storage and manipulation of image data

The Java 2D API also enables you to store and to manipulate image data--for example, you can easily perform image-filter operations, such as blur and sharpen, as shown in the following figure.

Slide 20 : Overview of the Java 2D API

The Java 2D API introduced in JDK 1.2 provides enhanced two-dimensional graphics, text, and imaging capabilities for Java programs through extensions to the Abstract Windowing Toolkit (AWT). This comprehensive rendering package supports line art, text, and images in a flexible, full-featured framework for developing richer user interfaces, sophisticated drawing programs and image editors.

The Java 2D API provides

A uniform rendering model for display devices and printers
A wide range of geometric primitives, such as curves, rectangles, and ellipses and a mechanism for rendering virtually any geometric shape
Mechanisms for performing hit detection on shapes, text, and images
A compositing model that provides control over how overlapping objects are rendered
Enhanced color support that facilitates color management
Support for printing complex documents

These topics are discussed in the following sections:

Slide 21 : Java 2D Rendering

Java 2D Rendering

The basic rendering mechanism is the same as in previous versions of the JDK--the drawing system controls when and how programs can draw. When a component needs to be displayed, its paint or update method is automatically invoked with an appropriate Graphics context.

The Java 2D API introduces java.awt.Graphics2D, a new type of Graphics object. Graphics2D extends the Graphics class to provide access to the enhanced graphics and rendering features of the Java 2D API.

To use Java 2D API features, you cast the Graphics object passed into a component's rendering method to a Graphics2D object.

public void Paint (Graphics g) {
    Graphics2D g2 = (Graphics2D) g;
    ...
}

Slide 22 : Java 2D Rendering Context

Graphics2D Rendering Context

The collection of state attributes associated with a Graphics2D object is referred to as the Graphics2D rendering context. To display text, shapes, or images, you set up the Graphics2D rendering context and then call one of the Graphics2D rendering methods, such as draw or fill. As the following figure shows, the Graphics2D rendering context contains several attributes.

To set an attribute in the `Graphics2D` rendering context, you use the `set` `Attribute` methods

The pen style : setStroke

that is applied to the outline of a shape. This stroke attribute enables you to draw lines with any point size and dashing pattern and to apply end-cap and join decorations to a line.

The fill style : setPaint

that is applied to a shape's interior. This paint attribute enables you to fill shapes with solid colors, gradients, and patterns.

The compositing style : setComposite

that is used when rendered objects overlap existing objects.

The transform : setTransform

that is applied during rendering to convert the rendered object from user space to device-space coordinates. Optional translation, rotation, scaling, or shearing transforms can also be applied through this attribute.

The clip : setClip

which restricts rendering to the area within the outline of the Shape used to define the clipping path. Any Shape can be used to define the clip.

The font :setFont

used to convert text strings to glyphs.

Rendering hints : setRenderingHints

that specify preferences in the trade-offs between speed and quality. For example, you can specify whether antialiasing should be used, if it's available.

Slide 23 : Rendering Methods

Rendering Methods

Example

When you set an attribute, you pass in the appropriate attribute object. For example, to change the paint attribute to a blue-green gradient fill, you would construct a GradientPaint object and then call setPaint.

gp = new GradientPaint(0f,0f,blue,0f,30f,green);
g2.setPaint(gp);

Graphics2D holds references to its attribute objects--they are not cloned. If you alter an attribute object that is part of the Graphics2D context, you need to call the appropriate set method to notify the context. Modifying an attribute object during rendering causes unpredictable behavior.

Graphics2D Rendering Methods

Graphics2D provides the following general rendering methods that can be used to draw any geometry primitive, text, or image:

draw
--renders the outline of any geometry primitive, using the stroke and paint attributes.
fill--renders any geometry primitive by filling its interior with the color or pattern specified by the paint attribute.
drawString--renders any text string. The font attribute is used to convert the string to glyphs, which are then filled with the color or pattern specified by the paint attribute.
drawImage--renders the specified image.

In addition, Graphics2D supports the Graphics rendering methods for particular shapes, such as drawOval and fillRect.

Slide 24 : Coordinate Systems

Coordinate Systems

The Java 2D system maintains two coordinate spaces.

User space
is the space in which graphics primitives are specified.
Device space
is the coordinate system of an output device, such as a screen, window, or a printer.

User space is a device-independent logical coordinate system : the coordinate space that your program uses.
All geometries passed into Java 2D rendering routines are specified in user-space coordinates.

Default transformation

When the default transformation from user space to device space is used, the origin of user space is the upper-left corner of the component's drawing area. The x coordinate increases to the right, and the y coordinate increases downward, as shown in the following figure.

Device space is a device-dependent coordinate system that varies according to the target rendering device. Although the coordinate system for a window or the screen might be very different from that of a printer, these differences are invisible to Java programs. The necessary conversions between user space and device space are performed automatically during rendering.

Slide 25 : Shapes

Shapes

The classes in the java.awt.geom package define common graphics primitives, such as points, lines, curves, arcs, rectangles, and ellipses.

Classes in the java.awt.geom Package
Arc2D	Ellipse2D	QuadCurve2D
Area	GeneralPath	Rectangle2D
CubicCurve2D	Line2D	RectangularShape
Dimension2D	Point2D	RoundRectangle2D

Each geometry classes implements the `Shape` interface

Except for Point2D and Dimension2D, each of the geometry classes (geometries) implements the Shape interface, which provides a common set of methods for describing and inspecting two-dimensional geometric objects.

draw or fill method

With these classes you can create virtually any geometric shape and render it through Graphics2D by calling the draw method or the fill method.

For example, the geometric shapes in the following ShapesDemo2D applet are defined by using basic Java 2D geometries.

Example : ShapesDemo2D.java.

Rectangular Shapes

The Rectangle2D, RoundRectangle2D, Arc2D, and Ellipse2D primitives are all derived from RectangularShape, which defines methods for Shape objects that can be described by a rectangular bounding box. The geometry of a RectangularShape can be extrapolated from a rectangle that completely encloses the outline of the Shape.

QuadCurve2D and CubicCurve2D

The QuadCurve2D class allows you to create quadratic parametric curve segments. A quadratic curve is defined by two endpoints and one control point.

The CubicCurve2D class allows you to create cubic parametric curve segments. A cubic curve is defined by two endpoints and two control points. The following figures demonstrate examples of quadratic and cubic curves.

See Stroking and Filling Graphics Primitives to see implementations of cubic and quadratic curves.

GeneralPath

The GeneralPath class enables you to construct an arbitrary shape by specifying a series of positions along the shape's boundary. These positions can be connected by line segments, quadratic curves, or cubic (Bézier) curves. The shape pictured below can be created with three line segments and a cubic curve.

See Stroking and Filling Graphics Primitives to see the implementation of this shape.

Areas

With the Area class you can perform boolean operations, such as union, intersection, and subtraction, on any two Shape objects. This technique, often referred to as constructive area geometry, enables you to quickly create complex Shape objects without having to describe each line segment or curve.

How to draw and fill shapes is described in the next lesson, Displaying Graphics with Graphics2D.

Now, let's have a first look at an example.

Example : ShapesDemo2D.java.

Slide 26 : Stroking and Filling Graphics Primitives

Stroking and Filling Graphics Primitives

By changing the stroke and paint attributes in the Graphics2D context before rendering, you can easily apply fancy line styles and fill patterns to graphics primitives. For example, you can draw a dashed line by creating an appropriate Stroke object and calling setStroke to add it to the Graphics2D context before you render the line. Similarly, you can apply a gradient fill to a Shape by creating a GradientPaint object and adding it to the Graphics2D context by calling setPaint before you render the Shape.

The following applet demonstrates how you can render basic geometries by using the Graphics2D draw and fill methods.

ShapesDemo2D.java contains the complete code for this applet.

Each of the shapes drawn by the applet is constructed from one of the geometries and is then rendered through Graphics2D. The rectHeight and rectWidth variables in this example define the dimensions of the space where each shape is drawn, in pixels. The x and y variables change for each shape so that they are drawn in a grid formation.

	// draw Line2D.Double g2.draw(new Line2D.Double(x, y+rectHeight-1, x + rectWidth, y));
	// draw Rectangle2D.Double g2.setStroke(stroke); g2.draw(new Rectangle2D.Double(x, y, rectWidth, rectHeight));
	// draw RoundRectangle2D.Double g2.setStroke(dashed); g2.draw(new RoundRectangle2D.Double(x, y, rectWidth, rectHeight, 10, 10));
	// draw Arc2D.Double g2.setStroke(wideStroke); g2.draw(new Arc2D.Double(x, y, rectWidth, rectHeight, 90, 135, Arc2D.OPEN));
	// draw Ellipse2D.Double g2.setStroke(stroke); g2.draw(new Ellipse2D.Double(x, y, rectWidth, rectHeight));
	// draw GeneralPath (polygon) int x1Points[] = {x, x+rectWidth, x, x+rectWidth}; int y1Points[] = {y, y+rectHeight, y+rectHeight, y}; GeneralPath polygon = new GeneralPath(GeneralPath.WIND_EVEN_ODD, x1Points.length); polygon.moveTo(x1Points[0], y1Points[0]); for (int index = 1; index < x1Points.length; index++) { polygon.lineTo(x1Points[index], y1Points[index]); }; polygon.closePath(); g2.draw(polygon);
	// draw GeneralPath (polyline) int x2Points[] = {x, x+rectWidth, x, x+rectWidth}; int y2Points[] = {y, y+rectHeight, y+rectHeight, y}; GeneralPath polyline = new GeneralPath(GeneralPath.WIND_EVEN_ODD, x2Points.length); polyline.moveTo (x2Points[0], y2Points[0]); for (int index = 1; index < x2Points.length; index++) { polyline.lineTo(x2Points[index], y2Points[index]); }; g2.draw(polyline);
	// fill Rectangle2D.Double (red) g2.setPaint(red); g2.fill(new Rectangle2D.Double(x, y, rectWidth, rectHeight));
	// fill RoundRectangle2D.Double g2.setPaint(redtowhite); g2.fill(new RoundRectangle2D.Double(x, y, rectWidth, rectHeight, 10, 10));
	// fill Arc2D g2.setPaint(red); g2.fill(new Arc2D.Double(x, y, rectWidth, rectHeight, 90, 135, Arc2D.OPEN));
	// fill Ellipse2D.Double g2.setPaint(redtowhite); g2.fill (new Ellipse2D.Double(x, y, rectWidth, rectHeight));
	// fill and stroke GeneralPath int x3Points[] = {x, x+rectWidth, x, x+rectWidth}; int y3Points[] = {y, y+rectHeight, y+rectHeight, y}; GeneralPath filledPolygon = new GeneralPath(GeneralPath.WIND_EVEN_ODD, x3Points.length); filledPolygon.moveTo(x3Points[0], y3Points[0]); for (int index = 1; index < x3Points.length; index++) { filledPolygon.lineTo(x3Points[index], y3Points[index]); }; filledPolygon.closePath(); g2.setPaint(red); g2.fill(filledPolygon);

Note that this example uses the double-precision implementations of the geometries classes. Where applicable, float and double-precision implementations of each of the geometries are provided as inner classes.

Drawing Curves

The Cubic and Quad applets demonstrate how to create cubic and quadratic curves using CubicCurve2D and QuadCurve2D respectively. These applets also demonstrate how the curves are drawn with respect to the positioning of the control points by allowing you to interactively move both the control points and the end points.

Example: Quad

The Quad applet demonstrates a quadratic curve, which is a curved segment that has two endpoints and only one control point. The control point determines the shape of the curve by controlling both of the endpoint tangent vectors.

Quad.java contains the complete code for this applet.

First, a new quadratic curve is created with two endpoints and a control point and the locations of the points are set with respect to the size of the window.

QuadCurve2D.Double quad = new QuadCurve2D.Double();

Point2D.Double start, end, control;
start = new Point2D.Double();
end = new Point2D.Double();
control = new Point2D.Double();

quad.setCurve(start, control, end);

start.setLocation(w/2-50, h/2);
end.setLocation(w/2+50, h/2);
control.setLocation((int)(start.x)+50, (int)(start.y)-50);

Every time the user moves one of the points, the curve is reset.

quad.setCurve(start, control, end);

Example: Cubic

The Cubic sample demonstrates a cubic curve, which is a curved segment that has two endpoints and two control points. Each control point determines the shape of the curve by controlling one of the endpoint tangent vectors. In the Cubic sample, colored squares are drawn where the control points and endpoints are located. The blue control point controls the tangent vector of the red endpoint and the green control point controls the tangent vector of the magenta endpoint.

Cubic.java contains the complete code for this applet.

A new cubic curve is created with two endpoints and a two control points and the locations of the points are set with respect to the size of the window.

        
CubicCurve2D.Double cubic = new CubicCurve2D.Double();
        
Point2D.Double start, end, one, two;
start = new Point2D.Double();
one = new Point2D.Double();
two = new Point2D.Double();
end = new Point2D.Double();

cubic.setCurve(start, one, two, end);

...

start.setLocation(w/2-50, h/2);
end.setLocation(w/2+50, h/2);
one.setLocation((int)(start.x)+25, (int)(start.y)-25);
two.setLocation((int)(end.x)-25, (int)(end.y)+25);

As in the Quad example, the curve is reset every time the points are moved.

cubic.setCurve(start, one, two, end);

Drawing Arbitrary Shapes

The ShapesDemo example uses GeneralPath to make the hourglass-shaped polygons, but you can also use GeneralPath to make arbitrary shapes with both straight and curved lines.
Example: Odd_Shape
The Odd_Shape sample uses GeneralPath to create the arbitrary shape shown in the Shapes section.

Odd_Shape.java contains the complete code for this applet.
The following code creates a new GeneralPath and adds the first point to the path.
GeneralPath oddShape = new GeneralPath();
...

x = w/2 + 50;
y = h/2 - 25;

x2 = x; 
y2 = y;

oddShape.moveTo(x, y);
After the first point is added to the path, three straight lines are added to the path.
x -= 100;
oddShape.lineTo(x, y);
y += 50;
oddShape.lineTo(x, y);
x += 100;
oddShape.lineTo(x, y);
Finally, a cubic curve is added to the path.
x += 10;
y -= 10;
x1 = x - 20;
y1 = y - 20;
oddShape.curveTo(x, y, x1, y1, x2, y2);

Defining Fancy Line Styles and Fill Patterns

You probably noticed that in the previous example some of the shapes have thicker outlines or are filled with a two-color gradient. Using the Java 2D Stroke and Paint classes, you can easily define fancy line styles and fill patterns.

Line Styles

Line styles are defined by the stroke attribute in the Graphics2D rendering context. To set the stroke attribute, you create a BasicStroke object and pass it into the Graphics2D setStroke method.
A BasicStroke object holds information about the line width, join style, end-cap style, and dash style. This information is used when a Shape is rendered with the draw method.
The line width is the thickness of the line measured perpendicular to its trajectory. The line width is specified as a float value in user coordinate units, which are roughly equivalent to 1/72 inch when the default transform is used.
The join style is the decoration that is applied where two line segments meet. BasicStroke supports three join styles:
JOIN_BEVEL
JOIN_MITER
JOIN_ROUND
The end-cap style is the decoration that is applied where a line segment ends. BasicStroke supports three end-cap styles:
CAP_BUTT
CAP_ROUND
CAP_SQUARE
The dash style defines the pattern of opaque and transparent sections applied along the length of the line. The dash style is defined by a dash array and a dash phase. The dash array defines the dash pattern. Alternating elements in the array represent the dash length and the length of the space between dashes in user coordinate units. Element 0 represents the first dash, element 1 the first space, and so on. The dash phase is an offset into the dash pattern, also specified in user coordinate units. The dash phase indicates what part of the dash pattern is applied to the beginning of the line.

Fill Patterns

Fill patterns are defined by the paint attribute in the Graphics2D rendering context. To set the paint attribute, you create an instance of an object that implements the Paint interface and pass it into the Graphics2D setPaint method.
Three classes implement the Paint interface: Color, GradientPaint, and TexturePaint. GradientPaint and TexturePaint are new in JDK 1.2.
To create a GradientPaint, you specify a beginning position and color and an ending position and color. The gradient changes proportionally from one color to the other along the line connecting the two positions.

The pattern for a TexturePaint is defined by a BufferedImage. To create a TexturePaint, you specify the image that contains the pattern and a rectangle that is used to replicate and anchor the pattern.

Example: StrokeAndFill
The StrokeAndFill applet allows the user to select a graphics primitive, a line style, and a paint style and to either stroke the object's outline, fill it with the selected paint, or stroke the object in black and then fill it with the selected paint.

This is a picture of the applet's GUI. To run the applet, click the picture. The applet will appear in a new browser window.

StrokeAndFill.java contains the complete code for this applet.
The primitives are initialized and entered into an array of Shape objects. The following code creates a Rectangle and an Ellipse2D.Double and enters them into the shapes array.
shapes[0] = new Rectangle(0, 0, 100, 100);
shapes[1] = new Ellipse2D.Double(0.0, 0.0, 100.0, 100.0);
To create a Shape object from a text string, you must first create a TextLayout object from the text string.
TextLayout textTl = new TextLayout("Text", 
	  new Font("Helvetica", 1, 96), 
	  new FontRenderContext(null, false, false));
The following lines transform the TextLayout so that it is centered on the origin and then enter the Shape object resulting from the call to getOutline into the shapes array.
AffineTransform textAt = new AffineTransform();
textAt.translate(0,
    (float)textTl.getBounds().getHeight());
shapes[2] = textTl.getOutline(textAt);
You can choose a primitive by accessing the appropriate index into the shapes array.
Shape shape = 
    shapes[Transform.primitive.getSelectedIndex()];
How rendering is performed depends on which rendering option is chosen.

When the user chooses stroke, Graphics2D.draw is called to perform the rendering. If text is chosen as the primitive, the glyph outlines are retrieved and then rendered with the draw method.
When the user chooses fill, Graphics2D.fill or Graphics2D.drawString is called to perform the rendering.
When the user chooses stroke and fill, fill or drawString is called to fill the Shape, and then draw is called to stroke its outline.

Note: To both fill and stroke a graphics primitive, you need to make two separate method calls: fill or drawString to fill its interior and draw to stroke its outline.

The three line styles used in this example--thin, thick, and dashed--are instances of BasicStroke.
// Sets the Stroke.
...
case 0 : g2.setStroke(new BasicStroke(3.0f)); break;
case 1 : g2.setStroke(new BasicStroke(8.0f)); break;
case 2 : float dash[] = {10.0f};
         g2.setStroke(new BasicStroke(3.0f,
             BasicStroke.CAP_BUTT,
             BasicStroke.JOIN_MITER,
             10.0f, dash, 0.0f));
         break;
The dash style in this example has 10 unit dashes alternating with 10 unit spaces. The beginning of the dash pattern is applied to the beginning of the line--the dash phase is set to 0.0.
Three paint styles are used in this example--solid, gradient, and polka. The solid-color paint style is an instance of Color, the gradient an instance of GradientPaint, and the pattern an instance of TexturePaint.
// Sets the Paint.
...
case 0 : g2.setPaint(Color.blue); break;
case 1 : g2.setPaint(new GradientPaint(0, 0,
                          Color.lightGray,
                          w-250, h, Color.blue, false));
         break;
case 2 : BufferedImage bi = new BufferedImage(5, 5,
                                BufferedImage.TYPE_INT_RGB);
         Graphics2D big = bi.createGraphics();
         big.setColor(Color.blue);
         big.fillRect(0, 0, 5, 5);
         big.setColor(Color.lightGray);
         big.fillOval(0, 0, 5, 5);
         Rectangle r = new Rectangle(0,0,5,5);
         g2.setPaint(new TexturePaint(bi, r));
         break;

Slide 27 : Images

Images

The Java 2D API implements a new imaging model that supports the manipulation of fixed-resolution images stored in memory. A new Image class in the java.awt.image package, BufferedImage, can be used to hold and to manipulate image data retrieved from a file or a URL. For example, a BufferedImage can be used to implement double buffering--the graphic elements are rendered off-screen to the BufferedImage and are then copied to the screen through a call to Graphics2D drawImage. The classes BufferedImage and BufferedImageOp also enable you to perform a variety of image-filtering operations, such as blur and sharpen. The producer/consumer imaging model providedin previous versions of the JDK is supported for backward compatibility.

	The pen style : `setStroke` that is applied to the outline of a shape. This stroke attribute enables you to draw lines with any point size and dashing pattern and to apply end-cap and join decorations to a line.
	The fill style : `setPaint` that is applied to a shape's interior. This paint attribute enables you to fill shapes with solid colors, gradients, and patterns.
	The compositing style : `setComposite` that is used when rendered objects overlap existing objects.
	The transform : `setTransform` that is applied during rendering to convert the rendered object from user space to device-space coordinates. Optional translation, rotation, scaling, or shearing transforms can also be applied through this attribute.
	The clip : `setClip` which restricts rendering to the area within the outline of the `Shape` used to define the clipping path. Any `Shape` can be used to define the clip.
	The font :`setFont` used to convert text strings to glyphs.
	Rendering hints : `setRenderingHints` that specify preferences in the trade-offs between speed and quality. For example, you can specify whether antialiasing should be used, if it's available.

eScience Lectures Notes : Introduction to Java and Java 2D

Introduction to Java 2D

Java Revisal

I will try to go trough quite quickly on that first part as it should be a revisal for most of view. If something is not clear, it is time to ask question now...

Java 2D

First look at the example : ShapesDemo2D.java

More In details...

Second look at the example : ShapesDemo2D.java

Object-Oriented Programming

Java supports the Object-Oriented Programming (OOP) approach.

OOP focuses on the design of data-types (called objects or classes) rather than algorithms

Why is this distinction important?

Objects are nouns, Algorithms are verbs

Which is an easier task?

identify the actions that apply to a given noun

identify those objects to which a given action might be applied

What is easier?

identifying similar object classes

specifying general-purpose algorithms

Advantages of OOP

promotes design abstraction (hiding details)

promotes code reuse

consolidates specification and interface ... encapsulation

CG Example

Object-Oriented Design

Procedural Design

Similar object classes

Common interfaces

Common usage

Code reuse-- inheritance

Defers implementation and algorithm decisions

Algorithm centered-- forces early implementation and algorithm decisions

Exposes more details

Difficult to extend

Difficult to maintain

Polymorphism

Polymorphism allows algorithms to be specified in terms of the most general (and/or reasonable) object type

Java Specifics : space and curly braces

A Java source program is composed of white space, comments, declarations, and statements.

There are lots of differents "rules and conventions" on using white space and curly braces.

Adopt a consistent style !

Comments

Next to white space, the most important parts of any Java program are its comments.

Inline comments:

Block comments:

Special Comments

Java provides a special form of comment for generating automatic documentation, and web pages. It uses a tool called javadoc. Within these special comment blocks several special variables, indicated by a leading @, are recognized.

Documentation comments:

Java Data Types

Variables in Java must be objects, arrays, or one of the primitive data types

Java has 8 primitive data types (boolean, byte, short, int, long, double, float, char)

All integer types are signed (and there is no unsigned keyword)

Unlike C and C++ char variables are 16 rather than 8 bits Because Java is Unicode compliant

Unlike C Type have a definitly fixed size in C, it used to depent on the compiler

Primitive data types are passed to method by value the actual value of a primitive type can only be modified by the methods of the declaring or derived object

Java Arrays

Java arrays fall between a primitive data type and an object

Properties of Java arrays:

can contain objects, primitive types, or other arrays

contents are accessed via zero-based positive integers enclosed within the brackets, [, and ]

declaration, creation and, value initialisation of arrays are distinct operations

created with the new operator

uninitialized arrays have a value of null

have a single instance variable called 'length'

checks at run time, that all accesses are between 0 and length - 1

passed to methods by reference

Java Objects

Objects are containers around aggregates of primitive types, arrays, and other objects

Properties of Classes

All Java code is contained within objects Excepted comments, import and package statements.

Objects are passed to methods by reference

Definition, declaration, and creation of objects are distinct

Instances of objects are created with new and have a value of null

Objects have four forms: the class, the abstract class, the inner class, and the interface

Java Statements

Statements are all that remains!

Individual statements are terminated by semicolons

Blocks of statements are grouped using braces, {, and }

Simplest statement is the expression.

An expression is a string of variables and constants separated by operators. Java allows the following set of operators within statements:

Algorithm centered--
forces early implementation
and algorithm decisions

Java has 8 primitive data types
(boolean, byte, short, int, long, double, float, char)

Unlike C and C++ char variables are 16 rather than 8 bits
Because Java is Unicode compliant

Unlike C Type have a definitly fixed size
in C, it used to depent on the compiler

Primitive data types are passed to method by value
the actual value of a primitive type can only be modified by the methods of the declaring or derived object

All Java code is contained within objects
Excepted comments, import and package statements.

An expression is a string of variables and constants separated by operators.
Java allows the following set of operators within statements:

Class variables and method distinctions
(this, super, abstract, final, static, instance, and class variables)

`JFrame` class is a Swing extension of the AWT `Frame` class (Swing adds a J).

Swing lives in `javax.swing.*`.

javax.swing
Class JFrame

`Frame` class

Component and Window classes
(particularly methods to resize and position the frame):