Programming

1. Programming • What is a program? • A set of instructions • Understood by a computer

2. What does a program look like? • An algorithm is a set of instructions designed to accomplish a specific goal • For a temperature f in Fahrenheit • Subtract 32 from f. • Divide f by 1.8. • Display the value of f. • [Converts to Celsius] • Don’t need to understand the goal to follow instructions

3. Programming Languages • A language is a tool with which we tell a computer an algorithm • Compilers translate from one computer language to another • Each language has own advantages and disadvantages

4. The Java Language • Widely Used • Can be compiled on many computer systems • Object Oriented (we’ll learn what this means later)

5. Event Driven Programming • Old programs would start with all input at once and run until completion • Event: An action, a mouse click, an item selected • Using events made easy in Java

6. A First Program import objectdraw.*; import java.awt.*; public class TouchyWindow extends WindowController { publicvoid onMousePress ( Location point ) { new Text("I’m touched", 40, 50, canvas ); } public void onMouseRelease( Location point ) { canvas.clear(); } }

7. What do all these words mean? • Let’s break the program apart

8. Some of the words • Class • A set, collection, group, or configuration containing members regarded as having certain attributes or traits in common. (American Heritage Dictionary) • Very similar meaning in Java

9. Software Libraries • Reuse code already written • extends • Builds upon an already written class • import • Allows the use of instructions written elsewhere

10. Parts of a Class • Body • Enclosed in the curly braces found on the line “public class…” • Methods: publicvoid onMousePress ( Location point ) { new Text( "I’m touched", 40, 50, canvas ); }

11. The Life of a Program • Write the Program • Translate the program into a language the computer understands • Run the Program

12. Integrated Development Environments • Eclipse • Professional Programming Tool • TouchyWindow in Eclipse

13. Integrated Development Environments • BlueJ • Designed to teach Java • TouchyWindow in BlueJ

14. Integrated Development Environments • Eclipse and BlueJ: • Available on Windows, MacOS, Unix • Free and downloadable

15. More Programming • Normal vs Graphics Coordinate Systems

16. Graphical Objects new Text ( "I’m Touched", 40, 50, canvas ); • new an instruction that tells we want to construct a new object • Text the object we want to construct • (…) comma delineated “parameters” that tell how to construct the object • ; semicolons are important too! • every command semicolon terminated

17. Graphical Objects new Text ( "I’m Touched", 40, 50, canvas );

18. Events public void onMousePress( Location point ) • Will run the code when mouse button is pressed • onMouseRelease: • Runs code when the buttons released • Many more mouse event handling methods

19. The begin Method public void begin(){ … } • begin method • Executed (run) exactly once for each program • Executed early in program’s life

20. Graphical Objects new Line( 100, 150, 200, 0 canvas);

21. Graphical Objects • New FilledRect( 10, 20, 30, 40, canvas ); • Creates a 30x40 rectangle • Upper left corner at (10,20) • new FilledOval( 10, 20, 30, 40, canvas); • Imagine a 30x40 rectangle at (10,20) • Draws the largest oval that can fit inside the imaginary rectangle

22. Mistakes? Impossible! • Sadly, computers read what is written, not the intention. • Errors will often generate complaints from the IDE. • Some complaints are more informative than others