Week 2 Recap
CSE 115 – Spring 2007
Object Oriented Program

System of objects that communicate
with one another to solve some
problem.
Objects

Objects are made up of:

Properties
• Features that describe an object

Capabilities
• Actions that an object can perform
Formalizing our Design

UML class diagrams
What is a class?
 Classes are the formal
specification of what we want our
objects to be and what we want
them to be able to do.

Class Boxes in UML
Working with Eclipse

Eclipse is an IDE that will help make
writing our programs easier
First we must Edit (write the program)
 Then Compile (Eclipse helps us with
this by doing it as we type)
 Then Run (We select Run from a
menu to run our programs)

Java Files
Java source code files end with a
.java extension
 Once the code has been compiled,
files with a .class extension are
created
 It is these .class files that are “run” by
the Java Virtual Machine.

Java Syntax
We need to learn about the syntax
(grammar) rules of Java so that our
programs will compile. Once our
program compiles, we can run it.
 Question: Just because a program
compiles, does that mean it will
execute correctly?

Java Syntax (cont)

Java is case sensitive (as is Unix)
Java Source Code File

Made up of:
Package declaration
 Class definition

Package Declaration

package identifier ;
package is a keyword in Java – a
word that has a special meaning
 identifier represents a name. Here we
are identifying a package by name.

Packages
Way to organize our classes so that
like classes are grouped together.
 Putting a class in a package forces
you to put those classes in the same
directory on the system.

Identifiers

Programmers can pick out identifiers if we
follow these rules.




Identifiers must begin with a letter or
underscore
Followed by zero or more letters, digits, or
underscores
No special characters allowed in an identifier
Keywords are not allowed to be identifiers
Identifiers (Style)
Rules are enforced by compiler.
 Style enforced by community (i.e. your
grade)
 Style for identifiers for packages is
that the first letter of a package name
is lower-case, all other letters are
lower-case, and we do not see
underscores in package names.

Nested Packages
You can put a package inside of
another package.
 This is indicated by using the dot
(period) in between package names.
 On the system, nested packages are
directories inside other directories.
 If you are using something outside of
your current package, you must give
the fully-qualified package name.

Class Definition

Made up of:
Class Header
 Class Body


Class Body is made up of:
Definitions of properties
 Definitions of capabilities

Class Header

public class identifier

public is a keyword that is an access control
modifier. It tells who has access to
something. If public, everyone has access.
class is another keyword that indicates we
are about to start the definition of a class.
The identifier here represents the name of
the class.


Names of Classes
Must follow rules of identifiers.
 Style: First letter upper-case, rest
lower-case. If more than one word,
capitalize each new word. No
underscores in class names.
 Whatever you name the class is
whatever you will name the file the
class is defined in.

Class Body
Starts with a {
 Ends with a }
