Swing Graphics● Empty Swing containers have no visual appearance

except for a background color● Every JComponent must have a paintComponent

method that is called when the component is first made visible or needs to be redrawn for some reason

● The JPanel component is a lightweight container, making it suitable as a drawing area

● A common way to do graphics is to extend the JPanel class and override the paintComponent method

The paintComponent Method● Called by the JVM when this component needs to

be redrawn● A single argument, the component's graphics

context (class: Graphics), is passed when paintComponent is called

● A Graphics object contains:– the component on which it draws– the current color and font– location origin– clipping information– and more

Graphics vs. Graphics2D● The Graphics class has limitations:

– Cannot use real number coordinates– Cannot draw dotted, dashed, or variable-width lines– Cannot easily draw complex curves or fill complex

shapes– Cannot use textures or gradient colors to fill shapes

● The newer Graphics2D class extends Graphics and provides these capabilities

● All GUI components use a Graphics2D object but paintComponent passes a Graphics object for backward compatibility

General Approachpublic class MyPanel extends JPanel {

// instance variables public MyPanel() { // public constructor }

// public methods

// private helper methods

public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2d = (Graphics2D)g; // drawing messages sent to g2d ... }}

The paintComponent Method

● super.paintComponent(g) is called first to ensure that painting responsibilities defined in JPanel are carried out

● You should not call paintComponent directly; it is called by the JVM when it needs to

● You can indirectly call paintComponent on a component by using component.repaint()

Some Basic Graphics Methods

● void setColor(Color color)● void setFont(Font font)● void drawString(String text, int x, int y)– (x,y)is the coordinate of the lower left corner of the

drawn string's leftmost character

Graphics Exampleimport javax.swing.*;import java.awt.*;

public class GraphicsPanel extends JPanel {

public GraphicsPanel() { setPreferredSize(new Dimension(200,200)); setBackground(Color.magenta); // panel color }

public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2D = (Graphics2D)g; g2D.setColor(Color.blue); // drawing color g2D.setFont(new Font("Helvetica", Font.BOLD, 24)); g2D.drawString("Hello World", 25, 25); }}

Graphics Example (cont'd)import javax.swing.*;import java.awt.*;import java.awt.event.*;

public class MainFrame extends JFrame {

public MainFrame() { setSize(new Dimension(500,300)); setLocation(100,100); addWindowListener(new WindowAdapter () { public void windowClosing(WindowEvent e) { dispose(); System.exit(0); } }); getContentPane().setLayout( new FlowLayout(FlowLayout.CENTER)); GraphicsPanel gp = new GraphicsPanel(); getContentPane().add(gp); setVisible(true); }

public static void main(String[] args) { new MainFrame(); }}

Display

Notes On The Example

● GraphicsPanel extends JPanel so that the paintComponent method can be overridden

● If you forget to call super's paintComponent method, you can get pixels from another desktop frame as background garbage

● The background color is associated with the panel; the paint color with the Graphics2D object

● The MainFrame class extends JFrame and an instance of it is created in the main method

Drawing Shapes

● You can draw any object that implements the java.awt.Shape interface.

● Example: suppose g2D is a Graphics2D object:

Shape s = ...;g2D.draw(s);

The Java library supplies a number of classesthat implement the Shape interface type.

Inheritance Hierarchy of Geometric Shape Classes

Line Shapes

● java.awt.geom.Line2D is an abstract class with two concrete subclasses that are also inner classes:– Line2D.Double– Line2D.Float

● A Line2D object represents a line segment in (x,y) coordinate space.

● To create a line segment, first create its endpoints using the java.awt.geom.Point2D class

Line Exampleimport java.awt.geom.*;... public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2D = (Graphics2D)g; Point2D.Double corner1 = new Point2D.Double(100, 50); Point2D.Double corner2 = new Point2D.Double(50, 150); Point2D.Double corner3 = new Point2D.Double(150, 150); Line2D.Double side1 = new Line2D.Double(corner1, corner2); Line2D.Double side2 = new Line2D.Double(corner2, corner3); Line2D.Double side3 = new Line2D.Double(corner3, corner1); g2D.draw(side1); g2D.draw(side2); g2D.draw(side3); }...

An Easier Way: Polygons

import java.awt.*;... public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2D = (Graphics2D)g; Polygon triangle = new Polygon(new int[] {100, 50, 150}, new int[] {50, 150, 150}, 3); g2D.draw(triangle); // produces same triangls as before }...

Polygon(int[] xpoints, int[] ypoints, int npoints)

java.awt.Polygon implements the Shape interface.

Specify the x and y coordinates of a closed polygon'svertices with the following constructor:

Rectangular Shapes● Abstract subclasses of RectangularShape:

– Rectangle2D, RoundRectangle2D– Ellipse2D, Arc2D

● Each has concrete .Double and .Float subclasses

● Each constructor requires x,y coordinate of upper left corner of bounding rectangle, and also the rectangle's width and height

● Use draw to draw an outline of the shape in the current color.

● Use fill to fill the shape with the current color.

Additional Parameters for Rounded Rectangles

arcWidth

arcHeight

(x,y)

height

width

Example public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2D = (Graphics2D)g;

Rectangle2D.Double rect1 = new Rectangle2D.Double(25,25,100,100); g2D.setColor(Color.black); g2D.draw(rect1);

RoundRectangle2D.Double rect2 = new RoundRectangle2D.Double(50,50,100,100,80,30); g2D.setColor(Color.green); g2D.fill(rect2);

Ellipse2D.Double rect3 = new Ellipse2D.Double(75,75,100,80); g2D.setColor(Color.blue); g2D.fill(rect3); }

New Display

Additional Parameters for Arcs

(x,y)

0

-270 90

±180

270-90

width

height

startAngleangularExtent

Closure type for the arc: OPEN, CHORD, or PIE

Arc Example

public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2D = (Graphics2D)g;

Arc2D.Double arc = new Arc2D.Double(25,25,150,100,0,120,Arc2D.PIE); g2D.setColor(Color.black); g2D.fill(arc);

arc = new Arc2D.Double(25,25,150,100,120,120,Arc2D.PIE); g2D.setColor(Color.green); g2D.fill(arc);

arc = new Arc2D.Double(25,25,150,100,240,120,Arc2D.PIE); g2D.setColor(Color.orange); g2D.fill(arc); }

Arc Display

Arc Example Modified

public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2D = (Graphics2D)g;

Arc2D.Double arc = new Arc2D.Double(25,25,150,100,0,120,Arc2D.CHORD); g2D.setColor(Color.black); g2D.fill(arc);

arc = new Arc2D.Double(25,25,150,100,120,120,Arc2D.CHORD); g2D.setColor(Color.green); g2D.fill(arc);

arc = new Arc2D.Double(25,25,150,100,240,120,Arc2D.CHORD); g2D.setColor(Color.orange); g2D.fill(arc); }

New Arc Display

More Features

● Other things you can do with Shapes:– Check for containment of points and rectangles– Get bounding rectangle– Check for intersection with another bounding

rectangle

● Other things you can do with 2D graphics contexts:– Change stroke properties– Draw images– Perform rotations, scalings, and translations