Programming What is a program? A set of instructions Understood by - PowerPoint PPT Presentation

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

What is Alice?  A programming environment.

What is Alice?  A programming language.  A library of graphic objects

What is Alice? A tool for running animations

What about JAVA?  BlueJ - a programming environment designed to teach programming

The Java Language  A programming language (Widely Used) 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(); } }  Can be compiled on many computer systems

What about Java?  A huge library, but less visual  2D Graphical shapes - circles, lines, …  User interface elements - buttons, sliders, …  Networking  Image manipulation  Many, many things  A tool for running a wide range of applications

Methods in Java 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(); } }

Types  Number  int  double  Boolean  boolean  Object  Penguin  Location  Train  …

Event Handling In Alice: In Java: 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(); } }

Creating Objects  In Java:  In Alice: In Java: 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(); } }

Anatomy of a Java Class: set, collection group, or configuration containing members regarded as having certain attributes or traits in common import objectdraw.*; import java.awt.*; public class TouchyWindow extends WindowController { parameter public void onMousePress ( Location point ) { new Text("I’m touched", 40, 50, canvas ); Instruction } Method public void onMouseRelease( Location point ) { canvas.clear(); } class }

Coordinate system  Coordinates measure pixels, the smallest dot of color a display can make

Methods and Constructors public class TouchyWindow extends WindowController { public void onMousePress ( Location point ) { Constructor call new Text("I’m touched", 40, 50, canvas ); } public void onMouseRelease( Location point ) { canvas.clear(); Method call } }

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 In Alice, need to specify which method to call when an event occurs Java: 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

Summary  Many similarities in programming concepts  Alice - limited to creating animations  Java - wide applicability  Alice programming environment - menu, drag&drop eliminates syntax errors, but clumsy  Java programming environment - less clumsy, but requires learning syntax