Programming What is a program? –A set of instructions –Understood by a computer

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

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

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

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

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

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

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

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

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

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

Integrated Development Environments Eclipse –Professional Programming Tool TouchyWindow in Eclipse

Integrated Development Environments BlueJ –Designed to teach Java TouchyWindow in BlueJ

Integrated Development Environments Eclipse and BlueJ: –Available on Windows, MacOS, Unix –Free and downloadable

More Programming Normal vs Graphics Coordinate Systems

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

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

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

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

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

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

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