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JAVA
Practical 02
1. Creating our first program
2. Source code file
3. Class file
4. Understanding the different parts of our program
5. Escape characters
6. Case sensitivity
7. Syntax Errors
First Steps

It is a good idea for to create a folder
where we will save our programs

So you simply create a folder in my
documents and name it ‘My Java’

J Creator is then used to create our
programs
JCreator

1.
2.
3.
4.
5.
In order to start programming we need
to create a new file in Jcreator
Start up JCreator
Click on File > New > File
Click on Empty Java File
Name the file as ‘Practical02’
Choose to save it in the folder you just
created in My Documents
First Program

Type in the following program

What should this program output?
Compiling our Program
When we compile our program we will
be building our file
 To compile our program we need to
press on the ‘Build File’ icon.
 If we have no errors it will show Process
Complete

Executing our Program
Executing means running our programs
 Once we compile it we can run our
program by pressing the run icon

Program Output

Once you press run a new window will
open showing your programs output
Source-Code File

The source-code file is the text file create
when we save a program

This file uses actual text which use
humans can read
Class File

A class file is the file created each time
we compile a program

The class file contains the code that the
JVM (Java Virtual Machine) uses to run
our programs.
Program Components
The different parts of our programs
Comments

//Program 1 : My First Program
Comments are used to remind the
programmer what the code does.
There are two type of comments; single line
and multi-line.
1. Single line comments: only a single line. In
order to create a single-line comment, //
must be used before writing the
comment.
2. Multi-line comments can be spread over a
number of lines, these comments must
start with /* and then end with */.

Class
class TestProgram

The keyword class shows that a new class
is being created

Just after the keyword, there must be the
name of the class, which is TestProgram in
our program

Then the curly brackets show where the
code of the class begins and ends.
Main Method
public static void main (String args[]){

Every program must have one main method
It is made up of :
1. public – this means that this method is available
from outside the class
2. static – this method can be used without
creating an instance of the class
3. void – this method does not return a value
4. main – the name of the method
5. String args[] – an array of type String which can
accept a number of arguments in array args

Statement
System.out.println("Hello World!");

This statement tells the program to print
Hello World! as the output
println() : tells the program to move the
cursor to the next line
 print(): tells the program to leave the
cursor on the same line

Semi - colon
;

All statements must end with a semi –
colon

The semi – colon lets the program know
that the statement is over and can be run
Escape Characters

These are used to edit the way the text is
printed when using println()
Escape Character
What it is used for
\’
Display in a single quote
\”
Display in double quotes
\\
Display a backslash
\n
Move to a new line
\t
Insert a tab
Case sensitivity

When programming in Java we have to be
careful to make sure that everything is
written correctly

It is important to look out when writing
words with capital letters and small
letters
If we write system.out.println("Hello World!");
we will get an error… why?

Syntax Error

An error in the code is called a Syntax error

The code will not compile before all the
errors are seen too
Errors could be;
1. Not obeying the case sensitivity rule
2. Forgetting a semi – colon
3. Forgetting brackets… ect
