Java HelloWorld and Language syntax.

1. Java Class
Java class has a State and Behavior

2. State (Variables)
Variable or Field is nothing but the property of the
class
class “computer” may have property like :
– Model
– mem_size
– hd_size
– os_type etc

3. Class Names
first letter should be
in Upper Case
If several words are used to form a name of the class each inner
words first letter should be in Upper Case.
Ex: MyFirstJavaExample

4. Behavior (Methods)
Method is nothing but the operation that an object
can perform
It tells How an object can interact with outside
world

5. Method Names
All method names should
start with a Lower Case letter.
Ex:
public void myMethodName( )

6. Java Application
Java classes having main method

7. main method
should be public
– because Class loader need to access this method
should be static
– because method would be executed without an
object

8. HelloWorld.java

9. Compile the source file

10. Java is Case Sensitive
● Both the compiler (javac) and launcher (java)
are case-sensitive.
● Type all code, commands, and file names
exactly as shown.
– HelloWorld is not the same as helloworld

11. Program File Name
Name of the program file should exactly match the
class name.
When saving the file you should save it using the
class name and append ‘.java’ to the end of the
name.
Example :
Assume ‘HelloWorld’ is the class name. Then the
file should be saved as ‘HelloWorld.java’

12. Java Identifiers
All java components require names.
Names used for classes, variables and methods
are called identifiers.

13. Java Keywords
These are reserved words and may not be used
as constant or variable or any other identifier
names.
Examples:
abstract, boolean, break, byte, class, package etc.

14. Comments in Java
Java supports single line and multi-line comments
very similar to c and c++.
All characters available inside any comment are
ignored by Java compiler.

15. Using Blank Lines
A line containing only whitespace is known as a
blank line, and Java ignores it.