Programming for Interactivity Professor Bill Tomlinson Tuesday & Wednesday 6:00-7:50pm Fall 2005

Computer Program A way to get a computer to do something

Programming Language A way of writing computer programs that is (potentially) comprehensible by people.

Interpreted vs. Compiled Interpreted – one line at a time. Compiled: Person-> Source Code -> Machine Code -> Computer

Source code Human-readable text that can be used to make a computer operate in a certain way.

Commenting A way to get the computer to ignore certain parts of a computer program. Useful for: –Identifying the function of certain lines of code –Temporarily removing parts of programs –Leaving notes for yourself and others

Object Oriented Programming Wikipedia – “the idea that a computer program is composed of a collection of individual units, or objects, as opposed to a traditional view in which a program is a list of instructions to the computer.”

Java A compiled language An object oriented language Derived largely from C/C++

Java Source Code /** * Written on Sep 26, 2005 by Bill Tomlinson */ public class MinimalPrintOutProgram { public static void main(String[] args) { //Note: this program is often called "Hello World." System.out.println("Hello there."); }

Curly Braces Demarcate different sections of code. Nested braces { Section 1 { Section 1a } { Section 1b }

Parentheses Different from curly braces Enclose arguments (we’ll get to arguments in a moment)

Semicolons There’s one at the end of every statement.

Line Spacing Irrelevant to the computer. Useful for keeping track of what is going on in complex code.

Classes These are the objects in “Object oriented programming”.

Fields Similar to nouns in the English language. They store data. Some important data types: –int – a number with no decimal places –float – a number with some decimal places –double – a number with lots of decimal places –String – a group of letters (and numbers) Give examples

Methods Like verbs in English Methods are actions that objects can perform They manipulate fields and interact with other objects.

Arguments Methods sometimes include arguments, that is, fields which are “passed in” to the method to allow it to act on them.

Types and Names Creates a reference to a chunk of memory of a certain type. May or may not put information into that memory space. int age; String name = “Bill”;

Arrays A way of grouping things String [] names = new String[3]; names[0] = “bill”;

Booleans true or false boolean myNameIsBill = true;

Loops Lets the program do something over and over again (which computers are very good at). for (int i = 0; i < 5; i ++) { System.out.println(“Round number “ + i); }

Conditionals if (age>18 && liveInUS) { vote(); }

System.out.println(); A way to print something out. Useful for debugging.

Three Kinds of Commenting // /* */ /** * */

// //This line is now commented out // I can also leave myself notes like this.

/* */ /* This kind of comment is useful for commenting out long blocks of code. */

/** * *This is yet a third kind of comment. *It is used to describe the content that *is coming next. * */

Capitalization By convention: ClassesAreCapitalizedLikeThis methodsAreCapitalizedLikeThis someFieldsAreCapitalizedLikeThis OTHER_FIELDS_LIKE_THIS (We’ll get to that distinction later.)

Field and Method Names Should be descriptive Long is okay. There are tools in Eclipse that make it easier. For now, even with notepad and javac, make sure to use descriptive names.

Questions about any of the letters? /** * Written on Sep 26, 2005 by Bill Tomlinson */ public class MinimalPrintOutProgram { public static void main(String[] args) { //Note: this program is often called "Hello World." System.out.println("Hello there."); }

A Longer Example (From your first assignment.)

Writing Code You may not (and probably won’t) understand everything about the code you’re working with.

Notepad, Javac and Java Walk through it together.

Applets Web based applications. Require one or more java class files and an html file.

Debugging Coding is an iterative process. Debugging is the bulk of the work, especially at first. Three Kinds of Bugs –Compile time –Run time –Misbehavior

Compile-Time Bugs Javac will not convert the.java files into.class files. Need to fix the code before you can even run it.

Run-Time Bugs Javac will converty the.java files into class files, but the code crashes somewhere. May crash before the code “works” at all, or it may crash after running for a while.

Misbehavior Code compiles and runs but… It doesn’t do what you want. Part of the challenge is often figuring out why it’s doing what it’s doing.

Assignment 1 Make a graphical computer program. You may use BasicGraphicsSystem.java, which I have provided, or you may use this as an opportunity to go learn JOGL or some other graphics system.

If There Is Time Left Start working on Assignment 1, and I will help out as needed.