Java Programming Fundamentals

•The basic structure in object-oriented
programming languages is a CLASS.
•Java programs are built using classes and
objects.
•A class is:
–a template or a blueprint
–Made up of ATTRIBUTES and BEHAVIOR
–Attributes are represented by variables and
behavior is revealed through methods

An example of a class (from Chapter 1)
–class Student
Student
name
age
course
studID
applyForEnrollment( )
payFees( )
class name
attributes / variables
behavior / methods

•Defining a class
In Java, a class is identified by a class name. To define
or declare a class:
class < ClassName > {
[ attribute/variable declarations ]
[ behavior/method declarations ]
}

•Conventions used
–Italicized words bounded by < > are programmer-
supplied
–Text in [ ] are optional
–Most object-oriented languages, such as Java, are
case-sensitive. Therefore, Student is different from
student.

Method
–Specifies the behavior(s) of a particular class, and is
defined within a class
–Contains a statement or set of statements that a
program must do or accomplish
–Identified by a method name, followed by a pair of
open and close parentheses
–It may or may not be bounded by a return statement

Defining a method
–To define or “declare” a method:
return-type < methodName > ( ) {
[statement 1];
[statement 2];
[return <variableName>]
}

•Problem:
–Write a program that would print out “I Love Java”
•Using the steps in program development from
chapter 1:
1.Problem Definition:
Print out “I Love Java”

2.Problem Analysis using HIPO Chart
INPUT PROCESS OUTPUT
“I Love Java” Print “I Love
Java”
printed “I Love
Java”

3.Program coding using java
1 public class GuirreLoveJava
2 /*
3 To display I LOVE JAVA
4 */
5 { public static void main(String[] args)
6 // prints the string “I LOVE JAVA” on the screen
7 { System.out.println(“I LOVE JAVA");
8 }
9 }

Steps in program coding using a text editor and
console:
1. Open a text editor such as Notepad or WordPad (for
Windows); vi for Linux or Unix.
2. Write or type your source code (as shown above) in
the text editor.
3. Save your file as: GuirreLoveJava.java. Don’t forget
that your file should have an extension of “.java”.

•4. Compile your program:
4a. In Windows, open another window in the MS-Dos
command prompt
4b. Go to the folder where your program
GuirreLoveJava.java is saved.
4c. To compile, type the command:
javac GuirreLoveJava.java
4d. Make sure there are no syntax (or typing) errors.

•5. Running your program:
5a. If the compilation from the previous step was
successful, a GuirreLoveJava.class file is created on
the current directory. Check to see if this file exists.
5b. To run your program, type the command:
java GuirreLoveJava

Explanation of the GuirreLoveJava program
•Line 1: The class name is “GuirreLoveJava”. Class
names start with a capital letter. Starting letters of
succeeding words are also capitalized.
• Lines 2 to 4: are comment lines describing what the
class does. These lines are skipped by the compiler.

•Line 5: A method named main( ) is declared inside the class.
• All applications must contain at least one main
method. Other methods can be declared but must not
be named “main”.
• When the program is run, main( ) is always the first
method to execute.
• All statements inside the main ( ) block are part of the
method

•Line 6: Another comment line describing what the main(
) method does
•Line 7: Prints out “GuirreLoveJava” on the screen
•Line 8: Ends the main( ) method
•Line 9: Ends the GuirreLoveJava class

Two types of errors occur when
compiling and running a program:
–Syntax Errors
–Runtime Errors

Syntax Errors
•Common errors in typing or in the use of some
keywords
•More complex syntax errors occur when certain
java object-oriented principles are violated
•When the java compiler detects these errors, it
displays error messages after the javac command

Runtime Errors
•Also called logic errors, these errors occur during
runtime and may or may not cause the program to
stop
•Some errors that do not cause the program to stop
are:
• Infinite loops
• Programs that display wrong outputs

Java Program Statements
–Inside the main ( ) method are statements that make
up the body of the program. When the program is run
these are executed by the Java Runtime Environment.
–Java program statements are terminated by a semi-
colon.

•A block is composed of several statements. A pair of curly
braces { } defines the scope of a block.
•The body of classes and methods are always defined
inside a block. This block defines the start and end points
of the class or method.
•Blocks can also be nested.

Comments
Programming statements that do not get compiled
and are not executed by the interpreter They are
written for documentation purposes
•3 types of comments
–Single line comments
–Multi-line comments
–Special javadoc comments

Single line (or C++ style) comments
start with //. All text after // are treated as comments
Example:
// This is an example of a single line comment

Multi-line (or C-style) comments
Are delimited by /* and */. All text between the two
delimiters are treated as comments. The comments can
span multiple lines.
Example:
/* This is an example of a comment spanning
multiple lines */

Special Javadoc comments
•Are used for generating an HTML documentation for
your java programs.
•It contains tags to add more information to your
comments. It can also span several lines.
•Example:
/** This is an example of a javadoc comments n for
generating an html documentation @author Claudio
Sanchez @version 1.3 */

Java Programming Fundamentals

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