Java Introduction, Evolution of Java, Java Architecture, Syntax of Java Program, Simple Java Program, Java Naming Convention, Java Comments

1. Fundamentals of JAVA
Dr. Kuppusamy .P
Associate Professor / SCOPE

2. Content
• Evolution of Java
• Java Architecture
• Syntax of Java Program
• Simple Java Program
• Naming Convention
• Comments
Dr. Kuppusamy P

3. Evolution of Java
• Java was the brainchild of:
• James Gosling
• Patrick Naughton
• Chris Warth
• Ed Frank
• Frank Sheridan
• The origin of Java is on fall of 1992, and was initially called
Oak
• Oak was renamed as Java in 1995
Goal
• Platform-neutral language used for embedded devices software
• Its portable
Dr. Kuppusamy P

4. Java Architecture
Dr. Kuppusamy P

5. Java Architecture
1. Create a java source code with .java extension
2. Compile the source code using java compiler which will create
bytecode file with .class extension
3. Class loader reads both the user defined and library classes into
the memory for execution
4. Bytecode verifier validates all the bytecodes are valid and do not
violate Java’s security restrictions
5. JVM reads bytecodes and translates into machine code for
execution. While execution of the program the code interacts to
the operating system and hardware
Dr. Kuppusamy P

6. 5 phases of Java Programs
1. Edit - Use an editor to type Java program (Welcome.java)
2. Compile - translate Java program into an intermediate language
called bytecodes, understood by Java interpreter (javac
Welcome.java)
1. Use a compiler to create .class file, containing bytecodes (Welcome.class)
3. Loader – Use a class loader to read bytecodes from .class file into
memory
4. Verifier - Use a Bytecode verifier to make sure bytecodes are
valid and do not violate security restrictions
5. Execute - Java Virtual Machine (JVM) uses a combination of
interpretation and just-intime compilation to translate bytecodes
into machine language
• Applications are run on user's machine, i.e. executed by interpreter with java
command (java Welcome)
Dr. Kuppusamy P

7. Java Virtual Machine (JVM)
• The output of the compiler is bytecode
• The bytecodes are executed by JVM
• It is an interpreter which converts the byte code to machine specific
instructions and executes
• JVM is platform specific
Dr. Kuppusamy P

8. Java Virtual Machine (JVM)
• Most modern languages are designed to be compiled
• Compilation is a one-time exercise and executes faster
• Execution of compiled code over the Internet an impossibility
• Executable code always generated to a CPU-OS combination
• Interpreting a Java program into byte code facilitates its execution
in a wide variety of environments
Dr. Kuppusamy P

9. Java Virtual Machine (JVM)
• Only the JVM needs to be implemented for each platform
• Once the Java runtime package exists for a given system, any Java
program can run on it
• The JVM will differ from Platform to Platform and it is Platform
Specific
• All versions of JVM interpret the same Java byte code
• Interpreted code runs much slower compared to executable code
• The use of bytecode enables the Java runtime system to execute
programs much faster
• Java facilitates on-the-fly compilation of bytecode into native code
Dr. Kuppusamy P

10. Adaptive optimizer (JIT Compiler)
• Another type of execution engine is an adaptive optimizer
• Speed up the execution
• The virtual machine starts by interpreting bytecodes
• It also keeps a tab on the code that is running and identifies only the heavily used
areas
• The JVM compiles these heavily used areas of code into native code
• The rest of the code, which is not heavily used continues to be interpreted and
executed
Preprocessor
• Preprocessor is a javac plugin that plugs directly into your Java compiler and
runs as part of javac.
• Not needed to add intermediate build steps, manage source generation targets.
• It’s effing fast and allows to easily build multiple targets from a single codebase.
Dr. Kuppusamy P

11. Class Loader / Linker
Class Loader / Linker
• class loader is a part of the VM that is important from:
• A security standpoint
• Network mobility
• The class loader loads a compiled Java source file (.class files represented as
bytecode) into the Java Virtual Machine (JVM)
• The bootstrap class loader (linker) is responsible for loading the classes,
programmer defined classes as well as Java's API classes
Java .class file
1. Java class file is designed for
• platform independence
• network mobility
2. The class file is compiled to a target JVM, but independent of underlying host
platforms
3. The Java class file is a binary file that has the capability to run on any platform
Dr. Kuppusamy P

12. Syntax of Java program
public class Classname
{
public static void main(String args[])
{
Statements
…..
}
}
Dr. Kuppusamy P
Create source file: Classname .java
Compile: javac Classname .java
Execute: java Classname
static – only one copy of memory is allotted (created) for the method main().
public – This main method can access by all members like objects, classes, etc
void – main() is not returns anything
String args[] – Input given in the console considered as string arguments

13. Simple Java program
public class Mobilephone {
public static void main(String args[]) {
System.out.println(“Experience the PUBG..!”);
} }
Output:
“Experience the PUBG..!”
Dr. Kuppusamy P
Create source file: Mobilephone .java
Compile: javac Mobilephone .java
Execute: java Mobilephone

14. Java program - Naming Conventions
Class Names
• Class names should be nouns, simple and descriptive
• Noun could be in mixed case with the first letter of each internal word capitalized
• Eg: class Student, class TestStudent
Variable Names
• The variables are in mixed case with a lowercase first letter
• Variable names should not start with underscore _ or dollar sign $, even though
both are allowed
• Variable names should be small and meaningful
• One-character variable names should be avoided except for temporary variables
• Eg: int y, myWidth;
Method Names
• Methods should be verbs, in mixed case with the first letter lowercase, with the
first letter of each internal word capitalized
• Eg: void run(), void getColor()
Dr. Kuppusamy P

15. Java program - Comments
Block (Multi-line) Comments
• Block comments are used to provide descriptions of files, methods, data structures
and algorithms
• Block comments may be used at the beginning of each file and before each method
/*
Here is a block comment
*/
Single line Comment
• Single line comments can be written using // Single line
Dr. Kuppusamy P

16. Number of Variables Declaration per Line
• One declaration per line is recommended
int height;
int width;
is preferred over
int height, width;
• Do not declare different types on the same line
int height, width[]; // Not recommended
Dr. Kuppusamy P

17. References
Dr. Kuppusamy P
Herbert Schildt, “Java: The Complete Reference”, McGraw-Hill Education, Tenth edition,
2017.