Download JavaIntro

Java Coding
Introduction
Scott McElfresh
SAMS 2004
Software Creation Cycle





Edit
Compile
Run
Test
Debug
Software Creation Cycle

Edit


Compile




java programname
sh run.sh
Test


javac programname.java
sh compile.sh
Run


word processor, text editor, Project Builder
make sure everything works as desired
Debug
Objects, Classes, and Behavior





In Java programming, items of interest are called objects
Objects that share common behavior are grouped into
classes.
Once a class is defined in Java, objects of that class can
be created. These are called instances.
Java has some classes pre-defined for us.
In this course, we will also use classes created by other
programmers.
Messages


Requesting that an object do something (execute
one of its behaviors) is called a sending a
message, or calling a method.
To send a message, we must specify the object
and the desired behavior. EG:



bob.goToStore();
jane.goToStore(butter); // butter is a “parameter”
bill.howOldAreYou()
Variables



Variables in Java refer to specific objects.
Java needs a way to refer to the object, so requires
an identifier.
Identifiers can have letters and numbers, and must
start with a letter.
Conditional code

Some actions are only desirable under certain conditions.
if (out of butter)
mary.goToStore(butter)

If statements allow us to check the state of the world and
make a decision about what to do.
if (mary.outOfButter())
mary.goToStore(butter);
else
mary.goToFriendsHouse();
Comments and
Internal Documentation




Comments are code for HUMANS to read, not the
computer.
/* …. */ indicates comments between.
// indicates comments on the rest of the line
Project builder typically makes these green.
Items on screen in this project

1.
2.
3.
4.
For each item on your screen, you need to do 3 or 4
things:
Choose a name for the item. Declare this to Java.
Create the item and fill in details (eg. location size)
Add it to your display and tell Java how this item relates
to other items on screen.
Tell Java what to do when this item is in focus and
phone keys are pressed.