Introduction to Java Chapter 8 - Introduction to Java Graphics1 Chapter 8 Introduction to Java Graphics

Chapter 8 - Introduction to Java Graphics 1

Introduction to Java

Chapter 8

Introduction to Java Graphics



Java Graphics Systems• The Java SDK contains to different graphics

systems– The Abstract Windowing Toolkit (AWT), which was

the original Java graphics system

– The Swing package, which is a newer, more flexible graphics system

• Only the Swing graphics system is taught in this text



Components and Containers• The two principal types of graphics objects are

Containers and Components

• A Component is visual object containing text or graphics– Here, we will work with a completely blank component,

known as a “Canvas”

• A Container is a graphical object that can hold components or other containers– The principal container is a Frame. It is a part of the

computer screen surrounded by borders and title bars.



Displaying Java Graphics• To display Java graphics:

1. Create the component or components to display

2. Create a frame to hold the component(s), and place the component(s) into the frame(s).

3. Create a “listener” object to detect and respond to mouse clicks, and assign the listener to the frame.

• The components in this chapter will be of class JCanvas, and the containers will be of class JFrame



Displaying Java Graphics (2) 1 import java.awt.*; 2 import java.awt.event.*; 3 import javax.swing.*; 4 import chapman.graphics.JCanvas; 5 public class TestJCanvas { 6 7 public static void main(String s[]) { 8 9 // Create a Window Listener to handle "close" events10 MyWindowListener l = new MyWindowListener();1112 // Create a blank yellow JCanvas13 JCanvas c = new JCanvas();14 c.setBackground( Color.yellow );1516 // Create a frame and place the canvas in the center17 // of the frame.18 JFrame f = new JFrame("Test JCanvas ...");19 f.addWindowListener(l);20 f.add(c, BorderLayout.CENTER);21 f.pack();22 f.setSize(400,400);23 f.show();24 }25 }

Required packages

Create component

Create “Listener”

Create frame

Add listener and com-ponent to frame



Listeners• A “Listener” class listens for mouse clicks or

keyboard input on a container or component, and responds when it occurs– In this chapter, we will use a “Window” listener to

detect mouse clicks and to shut down the program

1 class MyWindowListener extends WindowAdapter { 2 3 // This method implements a simple listener that detects 4 // the "window closing event" and stops the program. 5 public void windowClosing(WindowEvent e) { 6 System.exit(0); 7 }; 8 }

Trap mouse clicks in the “Close Window” box, and exit when one occurs



Displaying Graphics on a Component

• The paintComponent method is used to draw graphics on a component.– The calling sequence is: paintComponent( Graphics g )

– The Graphics object must be immediately cast to a java.awt.Graphics2D object before it can be used with Swing graphics

– Once this is done, all of the classes in java.awt.geom can be used to draw graphics on the component



Example: Drawing a Line

public class DrawLine extends JCanvas {

public void paintComponent ( Graphics g ) {

// Cast the graphics object to Graph2D Graphics2D g2 = (Graphics2D) g;

// Set background color Dimension size = getSize(); g2.setColor( Color.white ); g2.fill(new Rectangle2D.Double(0,0, size.width,size.height));

// Draw line g.setColor( Color.black ); Line2D line = new Line2D.Double (10., 10., 360., 360.); g2.draw(line); }......(main method inserted here)}

Create Line2D object

Draw line represented by object



The Graphics Coordinate System

• Java uses a graphics coor-dinate system with the origin (0,0) in the upper left-hand corner– x axis is positive to the right

– y axis is positive down

• By default, the units of measure are pixels– There are 72 pixels / inch

• Unit of measure can be changed

y-axis x-axis

origin



The Line2D Classes

• There are two concrete classes for creating lines: Line2D.Float and Line2D.Double. The only difference between them is the units of the calling parameters.

• Constructors:Line2D.Double( double x1, double y1, double x2, double y2 )

Line2D.Float( float x1, float y1, float x2, float y2 )

• These classes create a line from (x1,y1) to (x2,y2)



Controlling Object Color

• The color of a graphics object is controlled by the Graphics2D method setColor.

• The color may be any object of class java.awt. Color, including the following pre-defined values:

Color.black Color.magnetaColor.blue Color.orangeColor.cyan Color.pinkColor.darkGray Color.redColor.green Color.whiteColor.lightGray Color.yellow



Controlling Line Width and Style• Line width and style is controlled with a BasicStroke object

• Constructors have the form:BasicStroke(float width);

BasicStroke(float width, int cap, int join, float miterlimit,

float[] dash, float dash_phase);

• Can control line width, line cap style, line join style, and dashing pattern



Example: Setting Color and Stroke // This method draws two lines with color and styles. public void paintComponent ( Graphics g ) {

BasicStroke bs; // Ref to BasicStroke Line2D line; // Ref to line float[] solid = {12.0f,0.0f}; // Solid line style float[] dashed = {12.0f,12.0f}; // Dashed line style

// Cast the graphics object to Graph2D Graphics2D g2 = (Graphics2D) g;

...

// Set the Color and BasicStroke g2.setColor(Color.red); bs = new BasicStroke( 2.0f, BasicStroke.CAP_SQUARE, BasicStroke.JOIN_MITER, 1.0f, solid, 0.0f ); g2.setStroke(bs);

// Draw line line = new Line2D.Double (10., 10., 360., 360.); g2.draw(line);

// Set the Color and BasicStroke g2.setColor(Color.blue); bs = new BasicStroke( 4.0f, BasicStroke.CAP_SQUARE, BasicStroke.JOIN_MITER, 1.0f, dashed, 0.0f ); g2.setStroke(bs);

// Draw line line = new Line2D.Double (10., 300., 360., 10.); g2.draw(line); }

Set color

Set stroke

Draw line

Define stroke



The Rectangle2D Classes

• There are two classes for creating rectangles: Rectangle2D.Float and Rectangle2D.Double. The only difference between them is the units of the calling parameters.

• Constructors:Rectangle2D.Double( double x, double y, double w, double h )

Rectangle2D.Float( float x, float y, float w, float h )

• These classes create a rectangle with origin (x,y), with width w and height h



Example: Creating a Rectangle

bs = new BasicStroke( 3.0f, BasicStroke.CAP_SQUARE, BasicStroke.JOIN_MITER, 1.0f, solid, 0.0f );g2.setStroke(bs);

Rectangle2D rect = new Rectangle2D.Double (30., 40., 200., 150.);g2.setColor(Color.yellow);g2.fill(rect);g2.setColor(Color.black);g2.draw(rect);



The Ellipse2D Classes

• There are two classes for creating circles and ellipses: Ellipse2D.Float and Ellipse2D. Double. The only difference between them is the units of the calling parameters.

• Constructors:Ellipse2D.Double( double x, double y, double w, double h);

Ellipse2D.Float( float x, float y, float w, float h);

• These classes create the ellipse that fits in a rectangular box with origin (x,y), with width w and height h



Example: Creating an Ellipse

Ellipse2D rect = new Ellipse2D.Double (30., 40., 200., 150.);g2.setColor(Color.black);g2.fill(rect);



The Arc2D Classes• There are two classes for creating arcs: Arc2D.Float

and Arc2D.Double. • Constructors:

Arc2D.Double( double x, double y, double w, double h,

double start, double extent, int type );

Arc2D.Float( float x, float y, float w, float h,

float start, float extent, int type );

– These classes create an arc that fits in a rectangular box with origin (x,y), with width w and height h. The arc starts at start radians and extends for extent radians.

– The type of arc is Arc2D.OPEN, Arc2D.CHORD, or Arc2D.PIE



Example: Creating Arcs // Define arc1 arc = new Arc2D.Double (20., 40., 100., 150., 0., 60., Arc2D.PIE); g2.setColor(Color.yellow); g2.fill(arc); g2.setColor(Color.black); g2.draw(arc);

// Define arc2 arc = new Arc2D.Double (10., 200., 100., 100., 90., 180., Arc2D.CHORD); g2.setColor(Color.black); g2.draw(arc);

// Define arc3 arc = new Arc2D.Double (220., 10., 80., 200., 0., 120., Arc2D.OPEN); g2.setColor(Color.lightGray); g2.fill(arc); g2.setColor(Color.black); g2.draw(arc);

// Define arc4 arc = new Arc2D.Double (220., 220., 100., 100., -30., -300., Arc2D.PIE); g2.setColor(Color.orange); g2.fill(arc);



Displaying Text

• Text is displayed using the Graphics2D method drawString.

• Forms:drawString(String s, int x, int y);

drawString(String s, float x, float y);

• These methods write String s on the component. The point (x,y) specifies the lower-left hand corner of the text box within the component. – Note that this differs from the convention for other 2D

graphics objects, where (x,y) is the upper-left hand corner!



Example: Writing Text Strings

// Display string g2.setColor( Color.black ); g2.drawString("This is a test!",20,40);

This corner is (20,40)



Setting Fonts

• Fonts are created with the java.awt.Font class• Constructor:

Font( String s, int style, int size )

– s is the name for the font to use.– style is the style (Font.PLAIN, Font.BOLD, Font.ITALIC, or a combination)

– size is the font size in points

• Any font on the system may be used, but certain fonts are guaranteed to be present on any system



Standard Font Names

• The following standard fonts are present on any Java implementation:

Font Name DescriptionSerif This is the standard serif font for a particular

system. Examples are Times and Times NewRoman.

SansSerif This is the standard sansserif font for a particularsystem. Examples are Helvetica and Arial.

Monospaced This is the standard monospaced font for aparticular system. Examples are Courier andCourier New.

Dialog This is the standard font for dialog boxes on aparticular system.

DialogInput This is the standard font for dialog inputs on aparticular system.



Example: Defining Fonts

// Define several fonts... Font f1 = new Font("Serif",Font.PLAIN,12); Font f2 = new Font("SansSerif",Font.ITALIC,16); Font f3 = new Font("Monospaced",Font.BOLD,14); Font f4 = new Font("Serif",Font.BOLD+Font.ITALIC,20);

// Display fonts g2.setColor( Color.black ); g2.setFont(f1); g2.drawString("12-point plain Serif",20,40); g2.setFont(f2); g2.drawString("16-point italic SansSerif",20,80); g2.setFont(f3); g2.drawString("14-point bold Monospaced",20,120); g2.setFont(f4); g2.drawString("20-point bold italic Serif",20,160);



Getting Information About Fonts

• Class java.awt.FontMetrics can be used to get information about a font

• Constructor:FontMetrics fm = new FontMetrics( Font f );

FontMetrics fm = g2.getFontMetrics();

• Methods:Method Name Description

public int getAscent() Returns the ascent of a font in pixels.public int getDescent() Returns the descent of a font in pixels.public int getHeight() Returns the height of a font in pixels.public int getLeading() Returns the leading of a font in pixels.



Example: Getting Font Information

// Define a font... Font f1 = new Font("Serif",Font.PLAIN,14);

// Set font g2.setFont(f1);

// Get information about the font FontMetrics fm = g2.getFontMetrics();

// Get information about the current font System.out.println("Font metrics:"); System.out.println("Font height = " + fm.getHeight()); System.out.println("Font ascent = " + fm.getAscent()); System.out.println("Font descent = " + fm.getDescent()); System.out.println("Font leading = " + fm.getLeading());

D:\book\java\chap11>java ShowFontMetricsFont metrics:Font height = 20Font ascent = 15Font descent = 4Font leading = 1

Result:

Code:

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Introduction to Java Chapter 8 - Introduction to Java Graphics1 Chapter 8 Introduction to Java Graphics