The document discusses the Java Virtual Machine (JVM) and Runtime Environment (JRE). It explains that Java source code is compiled into bytecode that can run on any JVM, regardless of device. The JVM then interprets the bytecode and runs the program. It also introduces key Java concepts like data types, naming conventions, control structures, classes and objects.

1. Java Virtual Machine
and
Runtime Environment

2. Basic Concept
 When you write a program in C++ it is known as
source code.
 The C++ compiler converts this source code into the
machine code of underlying system (e.g. Windows)
 If you want to run that code on Linux you need to
recompile it with a Linux based compiler.
 Due to the difference in compilers, sometimes you
need to modify your code.

3. The Concept of WORA
 Java introduced WORA: Write Once Run Anywhere
 When you write a java program it is known as the source code of
java.
 The java compiler compiles this source code for a software system
known as JVM
 This compiled code is known as ‘Byte Code’
 We have different JVMs for different systems (such as JVM for
Windows , JVM for Linux etc).
 When we run our program the JVM interprets translates) the
compiled program into the language understood by the underlying
system.
 So we write our code once and the JVM runs it everywhere
according to the underlying system.

5. Byte Code
 Java programs (Source code) are compiled
into a form called Java bytecodes.
 The Java compiler reads Java language
source (.java) files, translates the source into
Java bytecodes, and places the bytecodes
into class (.class) files.
 The compiler generates one class file for
each class contained in java source file.

6. Java Virtual Machine
 The central part of java platform is java virtual
machine
 Java bytecode executes by special software known
as a "virtual machine".
 Most programming languages compile source code
directly into machine code, suitable for execution
 The difference with Java is that it uses bytecode - a
special type of machine code.
 The JVM executes Java bytecodes, so Java
bytecodes can be thought of as the machine
language of the JVM.

7. Java Virtual Machine

8. Java Runtime Environment(JRE)
 The Java Virtual Machine is a part of a large
system i.e. Java Runtime Environment(JRE).
 Each operating system and CPU architecture
requires different JRE.
 The JRE consists of set of built- in classes,
as well as a JVM.
 Without an available JRE for a given
environment, it is impossible to run Java
software.

9. Java Runtime Environment

10. First Java Program

11. Data Types
 The Java programming language is strongly-typed, which
means that all variables must first be declared before they can
be used.
int gear = 1;
 The eight primitive data types supported by the Java
programming language are:
– int, byte, short, long, float, double, boolean, char

12. Naming Conventions
 Java uses identifiers to name
– variables
– methods
– classes
– packages
 Syntax rules
– Must begin with a letter (upper- or lower-case)
– May be followed by any number (including 0) of letters and
digits
– The characters $ and _ are considered letters
– Java identifier names are case sensitive
– May not duplicate a Java keyword (e.g. class or main)

13. Escape Sequence

14. Control Structures
 Loops: for, while, do while
 If, if else, if else if, switch case

15. Class and object
 Class is a user defined data type.
 Object is variable of a class
– Data Members and Methods
 Constructor
 Method Overloading
 Inheritance
 Method Overriding