Java objects have state defined by variables and behavior defined by methods. State includes properties like model, memory size, etc. Class names use upper camel case and method names use lower camel case. The main method must be public, static, and without parameters to run a Java application from the command line. Comments and blank lines are ignored by the compiler.

1. Java object 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 Name
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 Name
All method names should
start with a Lower Case letter.
Ex:
public void myMethodName( )

6. Java Application
is a Java class having main method

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

8. HelloWorld.java

9. ● Compile the code
– javac HelloWorld.java
● Run the code
– java HelloWorld

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 :
class ‘HelloWorld’ should be saved in file ‘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.