Speed part 3

1. Speedpart 3 Barb Ericson Georgia Institute of Technology May 2006 Georgia Institute of Technology

2. Learning Goals • Computing Concepts • Write a compiler for a simple graphical language • Extend the compiler • Understand why compiled code is faster than interpreted code Georgia Institute of Technology

3. Writing a Compiler • To write a graphics compiler we need to • Write the code for a java class that draws the picture for the given graphics commands • We need to start the class definition including starting the main method – the prologue • Then we need to open the input file and output a line per command in the main • Then we need to finish the main method and class definition – the epilogue Georgia Institute of Technology

4. Creating a Graphics Compiler import java.io.*; /** * Class that reads in a file of graphics instructions, and * then generates a NEW Java Program that * does the same thing as the instructions. Default picture size is 640x480. * * Format of the file is a bunch of lines of the form: * Command X Y <parameters> * Commands are "line" with parameters of end X,Y and * "circle" with a parameter of diameter. * * For example: * line 10 10 50 70 * circle 10 20 30 * * Which draws a line from (10,10) to (50,70) and a circle at (10,20) * with a diameter of 30. * * @author Barb Ericson * @author Mark Guzdial */ Georgia Institute of Technology

5. Start of Class and writePrologue public class GraphicsCompiler { /** Method to write out the prologue for the new program: * All the imports, the class definition, main, etc. * @param file BufferedWriter to write the prologue to **/ public void writePrologue(BufferedWriter file){ try { // Write out the prologue lines file.write("import java.awt.*;"); file.newLine(); file.write("public class GeneratedDrawing{"); file.newLine(); file.write(" public static void main(String args[]){"); file.newLine(); file.write(" Picture frame = new Picture(640,480);"); file.newLine(); file.write(" Graphics g = frame.getGraphics();"); file.newLine(); file.write(" g.setColor(Color.black);"); file.newLine();} catch (Exception ex) { System.out.println("Error during write of prologue"); } } Georgia Institute of Technology

6. writeEpilogue Method /** Method to write out the epilogue for the new program: * Show the picture. Close the main and the class. * @param file BufferedWriter to write the epilogue to **/ public void writeEpilogue(BufferedWriter file){ try { // Write out the epilogue lines file.write(" frame.show();"); file.newLine(); file.write(" } // end main()"); file.newLine(); file.write("} // end class"); file.newLine();} catch (Exception ex) { System.out.println("Error during write of epilogue"); } } Georgia Institute of Technology

7. Start of CompileCommands Method /** * Method to compile the commands in the given file */ public void compileCommands(String fileName) { String line = null; String [] params = null; int x1, y1, x2, y2, diameter; // try the following try { // read from the file BufferedReader reader = new BufferedReader(new FileReader(fileName)); BufferedWriter writer = new BufferedWriter(new FileWriter( FileChooser.getMediaPath("GeneratedDrawing.java"))); writePrologue(writer); Georgia Institute of Technology

8. Loop and handle line command // loop till end of file while ((line = reader.readLine()) != null) { // what command is this? if (line.startsWith("line")) { // Get the parameters for drawing the line params = line.split(" "); // params[0] should be "line" x1 = Integer.parseInt(params[1]); y1 = Integer.parseInt(params[2]); x2 = Integer.parseInt(params[3]); y2 = Integer.parseInt(params[4]); // Now, write the line that will LATER // draw the line writer.write(" g.drawLine("+x1+","+y1+","+x2+","+y2+");"); writer.newLine(); } Georgia Institute of Technology

9. Handle circle command else if (line.startsWith("circle")) { // Get the parameters for drawing the circle params = line.split(" "); // params[0] should be "circle" x1 = Integer.parseInt(params[1]); y1 = Integer.parseInt(params[2]); diameter = Integer.parseInt(params[3]); // Now, draw the circle in writer.write(" g.drawOval("+x1+","+y1+","+diameter+","+ diameter+");"); writer.newLine(); } Georgia Institute of Technology

10. Finish compileCommand Method else { System.out.println("Uh-oh! Invalid command! "+line); return;} } writeEpilogue(writer); writer.close(); } catch (FileNotFoundException ex) { System.out.println("Couldn't find file " + fileName); fileName = FileChooser.pickAFile(); compileCommands(fileName); } catch (Exception ex) { System.out.println("Error during read or write"); ex.printStackTrace(); } } Georgia Institute of Technology

11. Main for Testing public static void main(String[] args) { GraphicsCompiler compiler = new GraphicsCompiler(); String fileName = FileChooser.getMediaPath( "graphics-commands.txt"); compiler.compileCommands(fileName); } } // end class Georgia Institute of Technology

12. How it Works • Open the same file for input as the interpreter • But don't create a blank picture to write to • Instead write to GeneratedDrawing.java • Write out a class definition • And a main that creates the blank picture, gets the graphics context on that picture, and does the drawing. • Compile GeneratedDrawing and execute it to see the picture Georgia Institute of Technology

13. Exercise • Add the code to handle triangles to the GraphicsCompiler class • triangle x1 y1 x2 y2 x3 y3 • It will draw a triangle with points at (x1,y1), (x2,y2), and (x3, y3) Georgia Institute of Technology

14. Compilers • Compilers still have to interpret the language they are compiling • But, they only do this one time • When you compile • Then you can execute the compiled code many times • Applications like Word or Photoshop are written in C or C++ and then compiled to machine language programs • The generated machine language program is faster than an interpreted one Georgia Institute of Technology

15. Summary • Compilers read a language and output the required code in another language • Like from our graphical language to Java commands • Or from C to machine language • You compile code once to turn it into the desired language • You can run the compiled code many times • Running compiled code is faster than running code that must be interpreted Georgia Institute of Technology