Java is a programming language and computing platform. Java is composed of a number of key components that, as a whole, create the Java platform. Two main components are : The Java Virtual Machine. The Java Application Programming Interface (API).

2. Write once, Run anywhere
Java Apps are
platform independent;
They can be run on
any OS having JVM.
If the OS does not have JVM then we
can not run Java App.

3. Java Byte code can only be
understandable by JVM.
Java class is written in Unicode
characters.
Java compiler convert these
Unicode characters into Byte
code.
JVM is native code and specific to OS

4. class file format
Java bytecode is the instruction set of the Java
virtual machine.

5. Java allows you to play
online games, chat with
people around the world,
calculate your mortgage
interest, and view images
in 3D, just to name a few.
It’s also integral to the intranet applications
and other e-business solutions that are
the foundation of corporate computing.

6. Java's sophisticated memory management, native
support for threading and concurrency, type
safety, and relative simplicity have created a
demand for its use in many domains.

7. Principles
There were five primary goals in the creation of the Java
language :
● simple, object-oriented and familiar
● robust and secure
● architecture-neutral and portable
● execute with “high performance”
● interpreted, threaded, and dynamic

8. Java platform
Java is a programming language and computing
platform.
Java is composed of a number of key components
that, as a whole, create the Java platform.
– The Java Virtual Machine
– The Java Application Programming Interface (API)
Java runs on more than 850 million personal
computers worldwide, and on billions of devices
worldwide, including mobile and TV devices.

9. Java API (Rich Standard Library)
The API is a large collection of ready-made
software components that provide many useful
capabilities. It is grouped into libraries of related
classes and interfaces; these libraries are known
as packages.
Java includes a vast number of premade
objects that can be used to perform such
tasks as input/output, networking, and date
manipulation.

10. java.lang
– Provides classes that are fundamental to the design
of the Java programming language.
java.io
– Provides for system input and output through data
streams, serialization and the file system.
java.sql
– Provides the API for accessing and processing data
stored in a data source

11. Java Environment
Java comes in two flavors :
● JRE - Java Runtime Environment
● JDK – Java Development Kit
You can download any of these two.

12. JRE
JRE provides components to run applications
written in the Java programming language :
● Java Virtual Machine
● Java API
● Tools to run Java Apps
The JRE does not contain tools and utilities such as
compilers or debuggers for developing applications.

13. Java Development Kit (JDK)
JDK is a superset of the JRE, and contains
everything that is in the JRE, plus tools such as
the compilers and debuggers necessary for
developing applications.
JDK is a collection of tools for developing,
packaging and distributing Java applications.

14. Java class loaders
The Java Classloader is a part of the JRE that
dynamically loads Java classes into the JVM.
Usually classes are only loaded on demand. The
Java run time system does not need to know
about files and file systems because of
classloaders.

15. Popular Java Editors
● Notepad++
● Eclipse