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Graphics in Java Applications

Graphics in Java Applications. The Graphics Class The Canvas Class The MouseListener Interface JavaDraw: A Demonstration of Graphics. Graphics in Java Applications. Can use turtle graphics for graphics, but very limited Turtle graphics screen is separate from rest of application

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Graphics in Java Applications

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  1. Graphics in Java Applications The Graphics Class The Canvas Class The MouseListener Interface JavaDraw: A Demonstration of Graphics

  2. Graphics in Java Applications • Can use turtle graphics for graphics, but very limited • Turtle graphics screen is separate from rest of application • User must press Continuous button to start turtle • No text in turtle drawing area • Will see how to use the Graphics class to draw shapes • Lines • Rectangles • Ovals • ... Programming and Problem Solving With Java

  3. The Graphics Class • Drawing directly on a frame is easiest approach • Later, will see how to draw on portion of a frame (canvas) • Use paint() method in Frame class to put graphical elements on the frame • Argument to Frame.paint() is Graphics object • Argument represents the drawing area of the frame Programming and Problem Solving With Java

  4. The Graphics Class: Text • Use Graphics.drawString() to put text in the graphics drawing area • Arguments • Text to display (as a string) • x (horizontal) position of the beginning of the text, in pixels • y (vertical) position of the beginning of the text, in pixels • 0,0 in upper left corner of frame • 0,0 is in the title bar area • Don’t write in title bar area -- it won’t show Programming and Problem Solving With Java

  5. The Graphics Class: Text • // Displays the string, "Hello!" at position 60, 80 of the frame. • import java.awt.*; • class DrawStringExample extends Frame • { • // Constructor • public DrawStringExample() • { • // Call the constructor for the Frame class with the title • // for the window • super("Test drawString()"); • // Set the size for the frame and display it • setSize(300, 300); • show(); • } • // paint: Display "Hello" • public void paint(Graphics g) • { • g.drawString("Hello!", 60, 80); • } • } • public class TestDrawString • { • public static void main(String[] args) • { • new DrawStringExample(); • } • } Programming and Problem Solving With Java

  6. The Graphics Class: Fonts • Can change text attributes with setFont() • setFont() argument:: a Font object • Font arguments • Name of installed font • Font style (Font.PLAIN, Font.ITALIC, Font.BOLD) • Point size • Font myFont = new Font("TimesRoman", Font.ITALIC, 28); • g.setFont(myFont); • Simpler approach • g.setFont(new Font("TimesRoman", Font.ITALIC, 28)); • Installed fonts on (nearly) any machine • TimeRoman • Helvetica • Courier Programming and Problem Solving With Java

  7. The Graphics Class: Fonts • // Demonstrates how to use fonts • import java.awt.*; • class FontsExample extends Frame • { • // Constructor • public FontsExample() • { • // Call the constructor for the Frame • // class with the title for the window • super("Test Fonts"); • // Set the size for the frame and display it • setSize(400, 250); • show(); • } • // paint: Display different fonts and styles • public void paint(Graphics g) • { • g.setFont(new Font("TimesRoman", Font.ITALIC, 28)); • g.drawString("Some Examples of Fonts", 20, 45); • g.setFont(new Font("Helvetica", Font.PLAIN, 12)); • g.drawString("This is an example of plain 12pt Helvetica font", 20, 70); • g.setFont(new Font("TimesRoman", Font.PLAIN, 12)); • g.drawString("This is an example of plain 12pt TimesRoman font", 20, 90); Programming and Problem Solving With Java

  8. The Graphics Class • g.setFont(new Font("Courier", Font.PLAIN, 12)); • g.drawString("This is an example of plain 12pt Courier font", 20, 110); • g.setFont(new Font("Helvetica", Font.ITALIC, 12)); • g.drawString("This is an example of italic 12pt Helvetica font", 20, 130); • g.setFont(new Font("TimesRoman", Font.ITALIC, 12)); • g.drawString("This is an example of italic 12pt TimesRoman font", 20, 150); • g.setFont(new Font("Courier", Font.ITALIC, 12)); • g.drawString("This is an example of italic 12pt Courier font”, 20, 170); • g.setFont(new Font("Helvetica", Font.BOLD, 12)); • g.drawString("This is an example of bold 12pt Helvetica font", 20, 190); • g.setFont(new Font("TimesRoman", Font.BOLD, 12)); • g.drawString("This is an example of bold 12pt TimesRoman font", 20, 210); • g.setFont(new Font("Courier", Font.BOLD, 12)); • g.drawString("This is an example of bold 12pt Courier font", 20, 230); • } • } • public class TestFonts • { • public static void main(String[] args) • { • new FontsExample(); • } • } Programming and Problem Solving With Java

  9. The Graphics Class: Colors • Use Graphics.setColor() to set color of Graphics object (before drawing it) • Can use RBG colors to specify exact color • Easiest way: use predefined constants in Color class: • Example • g.setColor(Color.blue); Programming and Problem Solving With Java

  10. The Graphics Class: Colors • // Demonstration of how to use colors • import java.awt.*; • class ColorsExample extends Frame • { • // Constructor • public ColorsExample() • { • // Call the constructor for the Frame class with the title • // for the window • super("Test Colors"); • // Set the size for the frame and display it • setSize(200, 100); • show(); • } • // paint: Display text with different colors • public void paint(Graphics g) • { • g.setColor(Color.red); • g.drawString("This is red", 20, 40); • g.setColor(Color.green); • g.drawString("This is green", 20, 60); • g.setColor(Color.blue); • g.drawString("This is blue", 20, 80); • } • public static void main(String[] args) • { • new ColorsExample(); • } • } Programming and Problem Solving With Java

  11. The Graphics Class: Lines • The drawLine() method draws a line between two points • Arguments • x position of beginning of line • y position of beginning of line • x position of end of line • y position of end of line • Example: draw line from 50, 50 to 100, 70 • g.drawLine(50, 50, 100, 70); Programming and Problem Solving With Java

  12. The Graphics Class: Lines • // Demonstration of the drawLine() method • import java.awt.*; • class DrawLineExample extends Frame • { • // Constructor • public DrawLineExample() • { • // Call the constructor for the Frame class with the title • // for the window • super("Test Drawing Lines"); • // Set the size for the frame and display it • setSize(200, 200); • show(); • } • // paint: Display a square with an X inside • public void paint(Graphics g) • { • g.drawLine(40, 40, 40, 160); • g.drawLine(40, 160, 160, 160); • g.drawLine(160, 160, 160, 40); • g.drawLine(160, 40, 40, 40); • g.drawLine(40, 40, 160, 160); • g.drawLine(40, 160, 160, 40); • } • } Programming and Problem Solving With Java

  13. The Graphics Class: Lines • public class TestDrawLine • { • public static void main(String[] args) • { • new DrawLineExample(); • } • } Programming and Problem Solving With Java

  14. The Graphics Class: Rectangles • The drawRect() method draws a rectangle between two points • Arguments • x position of beginning of upper left corner • y position of beginning of upper left corner • width of rectangle • height of rectangle • Orientation is fixed (can’t rotate 45 degrees, say) • Example: draw rectangle with 50, 50 upper left corner, width 100, height 70 • g.drawRect(50, 50, 100, 70); Programming and Problem Solving With Java

  15. The Graphics Class: Rectangles • // Demonstration of the drawRect() method • import java.awt.*; • class DrawRectanglesExample extends Frame • { • // Constructor • public DrawRectanglesExample() • { • // Call the constructor for the Frame class with the title • // for the window • super("Test Drawing Rectangles"); • // Set the size for the frame and display it • setSize(200, 200); • show(); • } • // paint: Display overlapping rectangles • public void paint(Graphics g) • { • g.drawRect(40, 40, 100, 30); • g.drawRect(50, 60, 120, 70); • } • } • public class TestDrawRectangle • { • public static void main(String[] args) • { • new DrawRectanglesExample(); • } • } Programming and Problem Solving With Java

  16. The Graphics Class: Polygons • The drawPolygon() method draws a closed polygon • Square • Triangle • Rectangle • Any other closed shape (doesn’t need to be regular) • Argument: a Polygon object • Example • Polygon triangle = new Polygon(); • triangle.addPoint(20, 20); • triangle.addPoint(50, 100); • triangle.addPoint(80, 30); • Pass the Polygon object to drawPolygon() to draw it • g.drawPolygon(triangle); Programming and Problem Solving With Java

  17. The Graphics Class: Polygons • // Demonstration of drawPolygon() • import java.awt.*; • class DrawPolygonExample extends Frame • { • // Constructor • public DrawPolygonExample() • { • // Call the constructor for the Frame class with the title • // for the window • super("Test Drawing Polygon"); • // Set the size for the frame and display it • setSize(250, 200); • show(); • } • // paint: Build and display a polygon • public void paint(Graphics g) • { • Polygon poly = new Polygon(); • poly.addPoint(20, 60); • poly.addPoint(60, 40); • poly.addPoint(120, 60); • poly.addPoint(180, 140); • poly.addPoint(50, 160); • g.drawPolygon(poly); • } • } • public class TestDrawPolygon • { • public static void main(String[] args) • { • new DrawPolygonExample(); • } • } Programming and Problem Solving With Java

  18. The Graphics Class: Other Methods • The drawOval() method • x position of the upper left corner of the oval • y position of the upper left corner of the oval • width of the oval • height of the oval • The drawArc() method • Same arguments as drawOval() plus • Starting angle • Number of degrees • Example of drawArc(): draw C • g.drawArc(20, 20, 100, 100, 90, 180); Programming and Problem Solving With Java

  19. The Graphics Class: Other Methods • “Fill” versions of drawing methods • Fills the open space with the current color • Examples • fillRect() • fillOval() • fillArc() • fillPolygon() Programming and Problem Solving With Java

  20. The Canvas Class • Canvas covers just part of a Frame • Direct drawing to Canvas instead of Frame • Allows restricted drawing • (Like a Panel for GUI applications) • Each Canvas gets its own paint() method • paint() method for a Canvas only applies to that Canvas Programming and Problem Solving With Java

  21. The Canvas Class • // Demonstrates the use of Canvas objects • import java.awt.*; • class OvalCanvas extends Canvas • { • // paint: Draw a light gray filled oval • public void paint(Graphics g) • { • g.setColor(Color.lightGray); • g.fillOval(20, 20, 200, 100); • } • } • class RectangleCanvas extends Canvas • { • // paint: Draw a dark gray filled rectangle • public void paint(Graphics g) • { • g.setColor(Color.darkGray); • g.fillRect(30, 10, 50, 120); • } • } Programming and Problem Solving With Java

  22. The Canvas Class • class DrawCanvasExample extends Frame • { • // Constructor • public DrawCanvasExample() • { • // Call the constructor for the Frame class with the title • // for the window • super("Test Canvas"); • // Choose the layout manager and initialize it • setLayout(new GridLayout(1, 2)); • // Add components to frame • add(new OvalCanvas()); • add(new RectangleCanvas()); • // Set the size for the frame and display it • setSize(500, 200); • show(); • } • } • public class TestCanvas • { • public static void main(String[] • args) • { • new DrawCanvasExample(); • } • } Programming and Problem Solving With Java

  23. The MouseListener Interface • Can have program respond to mouse events in the drawing area (not just for buttons and menus) • MouseListener interface methods • mousePressed(): user pressed mouse button down • mouseReleased(): user released mouse button • mouseClicked(): user pressed and released mouse button without moving it • mouseEntered(): user moved mouse into drawing area • mouseExited(): user moved mouse out of drawing area • Argument for each method is MouseEvent object • getPoint() method returns mouse location as Point object with public x and y variables Programming and Problem Solving With Java

  24. The MouseListener Interface • // Demonstration of mouse events • import java.awt.*; • import java.awt.event.*; • import java.util.Vector; • class MouseListenerExample extends Frame implements MouseListener • { • public MouseListenerExample() • { • super("Test MouseListener"); • // Choose the layout manager and initialize it • setLayout(new BorderLayout()); • // Add listener for mouse • addMouseListener(this); • // Set the size for the frame and display it • setSize(200, 200); • show(); • } Programming and Problem Solving With Java

  25. The MouseListener Interface • // mousePressed: Display the screen location at which the • // user pressed the mouse button • public void mousePressed(MouseEvent event) • { • System.out.println("Mouse pressed at " + event.getPoint()); • } • // mouseReleased: Display the screen location at which the • // user released the mouse button • public void mouseReleased(MouseEvent event) • { • System.out.println("Mouse released at " + event.getPoint()); • } • // mouseClicked: Display the screen location at which the • // user clicked (pressed and released) the • // mouse button • public void mouseClicked(MouseEvent event) • { • System.out.println("Mouse clicked at " + event.getPoint()); • } Programming and Problem Solving With Java

  26. The MouseListener Interface • // mouseEntered: Display the screen location at which the • // user moved the mouse into the frame • public void mouseEntered(MouseEvent event) • { • System.out.println("Mouse entered at " + event.getPoint()); • } • // mouseExited: Display the screen location at which the • // user moved the mouse out of the frame • public void mouseExited(MouseEvent event) • { • System.out.println("Mouse exited at " + event.getPoint()); • } • } • public class TestMouseListener • { • public static void main(String[] args) • { • new MouseListenerExample(); • } • } Programming and Problem Solving With Java

  27. The MouseListener Interface Programming and Problem Solving With Java

  28. The MouseListener Interface • Another example of MouseListener: Draw a line between mouse clicks • Steps • In mousePressed(), get location of mouse with getPoint(). Save location in instance variable beginPoint • In mouseReleased(), get location of mouse with getPoint(). Save location in instance variable endPoint Call repaint(), which calls paint()to redraw drawing area • In paint(), use drawLine() to draw line between beginPoint and endPoint Programming and Problem Solving With Java

  29. The MouseListener Interface • // This program shows how to use mouse events to • // control where lines are drawn on the frame. When the user • // clicks the mouse button down, drags the mouse, and releases • // the button, the program draws a line between those two points. • // The frame will only display one line at a time. • import java.awt.*; • import java.awt.event.*; • class LineDrawFrame extends Frame implements MouseListener • { • // Constructor • public LineDrawFrame() • { • super("Test MouseListener with Lines"); • // Choose the layout manager and initialize it • setLayout(new BorderLayout()); • // Add listener for mouse • addMouseListener(this); • // Set the size for the frame and display it • setSize(300, 200); • show(); • } Programming and Problem Solving With Java

  30. The MouseListener Interface • // mousePressed: When the user presses the mouse button, • // store the point of the click (this is the • // beginning point of the line) • public void mousePressed(MouseEvent event) • { • beginPoint = event.getPoint(); • } • // mouseReleased: When the user releases the mouse button, • // use the mouse's position as the end of the • // line, then draw the line with the repaint() • // method • public void mouseReleased(MouseEvent event) • { • endPoint = event.getPoint(); • repaint(); • } • // Unused MouseListener methods (but they must be defined in • // the program) • public void mouseEntered(MouseEvent event) {} • public void mouseClicked(MouseEvent event) {} • public void mouseExited(MouseEvent event) {} Programming and Problem Solving With Java

  31. The MouseListener Interface • // paint: Draw a line between beginPoint and endPoint • public void paint(Graphics g) • { • g.drawLine(beginPoint.x, beginPoint.y, endPoint.x, endPoint.y); • } • // Variables • Point beginPoint, endPoint; • } • public class LineDraw • { • public static void main(String[] args) • { • new LineDrawFrame(); • } • } Programming and Problem Solving With Java

  32. The MouseListener Interface • System will use paint() automatically when window is uncovered or resized • Program should use repaint() method to redraw • Calls paint() to redraw drawing area • Use whenever you want the system to use paint() • Don’t call paint() directly -- only run-time system should call paint() • Use repaint() when you know the drawing area needs to be updated, and run-time system won’t know this otherwise Programming and Problem Solving With Java

  33. JavaDraw Demonstration Programming and Problem Solving With Java

  34. JavaDraw Demonstration • Features • User can draw lines, rectangles, ovals with mouse • User clicks at starting point, then releases at ending point • User can clear the drawing area • User can undo actions, all the way to a blank drawing area • Demonstrates • Drawing shapes • Canvas • Border layout Programming and Problem Solving With Java

  35. JavaDraw Demonstration • Design of JavaDraw Programming and Problem Solving With Java

  36. JavaDraw Demonstration • Shape is abstract, with Line, Rectangle, and Oval subclasses • Allows easy storage of these subclasses in a Vector • Polymorphism: Vector (and supporting code) only deal with Shape objects Programming and Problem Solving With Java

  37. JavaDraw Demonstration • // This program is a simple drawing program. It • // allows the user to draw lines, rectangles, and ovals. The user • // can select the next shape to be drawn from a toolbar on the • // left side of the window. • // There are no editing or file handling features in this • // program. • // • // The program demonstrates the use of graphics in a Java • // program, and also shows how to handle mouse click events. • import java.awt.*; • import java.awt.event.*; • import java.util.Vector; • // ----------- Shape class -------------------------------------- • abstract class Shape • { • // draw: Draw the shape using the Graphics object g • abstract public void draw(Graphics g); • } Programming and Problem Solving With Java

  38. JavaDraw Demonstration • // ----------- Line class --------------------------------------- • class Line extends Shape • { • // Constructor • public Line(Point beginPoint, Point endPoint) • { • beginPoint = beginPoint; • endPoint = endPoint; • } • // draw: Draw the line using the Graphics object g • public void draw(Graphics g) • { • g.drawLine(beginPoint.x, beginPoint.y, • endPoint.x, endPoint.y); • } • // Variables • Point beginPoint, endPoint; • } Programming and Problem Solving With Java

  39. JavaDraw Demonstration • // ----------- Rectangle class --------------------------------- • class Rectangle extends Shape • { • // Constructor • public Rectangle(Point firstPoint, Point secondPoint) • { • upperLeftCorner • = new Point(Math.min(firstPoint.x, secondPoint.x), • Math.min(firstPoint.y, secondPoint.y)); • width = Math.abs(firstPoint.x - secondPoint.x); • height = Math.abs(firstPoint.y - secondPoint.y); • } • // draw: Draw the rectangle using the Graphics object g • public void draw(Graphics g) • { • g.drawRect(upperLeftCorner.x, upperLeftCorner.y, • width, height); • } • // Variables • Point upperLeftCorner; • int width, height; • } Programming and Problem Solving With Java

  40. JavaDraw Demonstration • // ----------- Oval class -------------------------------------- • class Oval extends Shape • { • // Constructor • public Oval(Point firstPoint, Point secondPoint) • { • upperLeftCorner • = new Point(Math.min(firstPoint.x, secondPoint.x), • Math.min(firstPoint.y, secondPoint.y)); • width = Math.abs(firstPoint.x - secondPoint.x); • height = Math.abs(firstPoint.y - secondPoint.y); • } • // draw: Draw the oval using the Graphics object g • public void draw(Graphics g) • { • g.drawOval(upperLeftCorner.x, upperLeftCorner.y, • width, height); • } • // Variables • Point upperLeftCorner; • int width, height; • } Programming and Problem Solving With Java

  41. JavaDraw Demonstration • // ----------- DrawCanvas class -------------------------------- • class DrawCanvas extends Canvas implements MouseListener • { • // Public constants • public static final int SHAPE_LINE = 1; • public static final int SHAPE_RECTANGLE = 2; • public static final int SHAPE_OVAL = 3; • // Constructor • public DrawCanvas() • { • // Add listener for mouse • addMouseListener(this); • } • // setShape: Change the shape of the next object to be drawn • // on the canvas to the given shape • public void setShape(int shape) • { • currentShape = shape; • } Programming and Problem Solving With Java

  42. JavaDraw Demonstration • // clear: Erase the canvas • public void clear() • { • shapeVector.removeAllElements(); • repaint(); • } • // undo: Remove the last-added shape (can be done any number • // of times • public void undo() • { • if (shapeVector.size() > 0) • { • shapeVector.setSize(shapeVector.size() - 1); • repaint(); • } • } • // mousePressed: When the user presses the mouse button, • // store the point of the click (this is the • // first sizing point of the new shape) • public void mousePressed(MouseEvent event) • { • beginPoint = event.getPoint(); • } Programming and Problem Solving With Java

  43. JavaDraw Demonstration • // mouseReleased: When the user releases the mouse button, • // use the mouse's position as the second • // sizing point (get the first sizing point from • // the beginPoint variable set in the • // mousePressed() method). Add the new shape • // to the vector of shapes, handy repaint the • // canvas. • public void mouseReleased(MouseEvent event) • { • switch (currentShape) • { • case SHAPE_LINE: • shapeVector.addElement(new Line(beginPoint, • event.getPoint())); • break; • case SHAPE_RECTANGLE: • shapeVector.addElement(new Rectangle(beginPoint, • event.getPoint())); • break; • case SHAPE_OVAL: • shapeVector.addElement(new Oval(beginPoint, • event.getPoint())); • } • repaint(); • } Programming and Problem Solving With Java

  44. JavaDraw Demonstration • // Unused MouseListener methods (but they must be defined in • // the program) • public void mouseEntered(MouseEvent event) {} • public void mouseClicked(MouseEvent event) {} • public void mouseExited(MouseEvent event) {} • // paint: Go through the vector of shapes and draw each one • // on the canvas • public void paint(Graphics g) • { • for (int i = 0; i < shapeVector.size(); i++) • { • ((Shape) shapeVector.elementAt(i)).draw(g); • } • } • // Variables • Point beginPoint; • int currentShape = SHAPE_LINE; // Default is to draw lines • Vector shapeVector = new Vector(); • } Programming and Problem Solving With Java

  45. JavaDraw Demonstration • // ----------- DrawFrame class --------------------------------- • class DrawFrame extends Frame implements ActionListener • { • // Interface variables • Button lineButton = new Button("Line"); • Button rectangleButton = new Button("Rectangle"); • Button circleButton = new Button("Oval"); • Button clearButton = new Button("Clear"); • Button undoButton = new Button("Undo"); • Button exitButton = new Button("Exit"); • DrawCanvas myDrawCanvas = new DrawCanvas(); • // Constructor • public DrawFrame() • { • // Call the constructor for the Frame class with the title • // for the window • super("Java Draw"); • // Choose the layout manager and initialize it • setLayout(new BorderLayout()); Programming and Problem Solving With Java

  46. JavaDraw Demonstration • // Make a "toolbar" panel out of the buttons • Panel toolbarPanel = new Panel(); • toolbarPanel.setLayout(new GridLayout(6, 1)); • toolbarPanel.add(lineButton); • toolbarPanel.add(rectangleButton); • toolbarPanel.add(circleButton); • toolbarPanel.add(clearButton); • toolbarPanel.add(undoButton); • toolbarPanel.add(exitButton); • // Add listener for buttons • lineButton.addActionListener(this); • rectangleButton.addActionListener(this); • circleButton.addActionListener(this); • clearButton.addActionListener(this); • undoButton.addActionListener(this); • exitButton.addActionListener(this); • // Add components to frame • add(toolbarPanel, BorderLayout.WEST); • add(myDrawCanvas, BorderLayout.CENTER); • // Set the size for the frame and display it • setSize(300, 300); • show(); • } Programming and Problem Solving With Java

  47. JavaDraw Demonstration • // actionPerformed: Set the shape in the myDrawCanvas object • // to the shape chosen by the user • public void actionPerformed(ActionEvent event) • { • if (event.getSource() == lineButton) • { • myDrawCanvas.setShape(DrawCanvas.SHAPE_LINE); • } • else if (event.getSource() == rectangleButton) • { • myDrawCanvas.setShape(DrawCanvas.SHAPE_RECTANGLE); • } • else if (event.getSource() == circleButton) • { • myDrawCanvas.setShape(DrawCanvas.SHAPE_OVAL); • } • else if (event.getSource() == clearButton) • { • myDrawCanvas.clear(); • } • else if (event.getSource() == undoButton) • { • myDrawCanvas.undo(); • } • else if (event.getSource() == exitButton) • { • setVisible(false); • dispose(); • System.exit(0); • } • } • } Programming and Problem Solving With Java

  48. JavaDraw Demonstration • // ----------- JavaDraw class ---------------------------------- • public class JavaDraw • { • public static void main(String[] args) • { • new DrawFrame(); • } • } Programming and Problem Solving With Java

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