JAVA programming notes

JAVA PROGRAMMING NOTES
PART 1

, MODULE 1


A Java virtual machine (JVM) is an abstract computing machine that enables a computer to
run a Java program. There are three notions of the JVM: specification, implementation, and
instance. The specification is a document that formally describes what is required of a JVM
implementation. Having a single specification ensures all implementations are interoperable. A
JVM implementation is a computer program that meets the requirements of the JVM
specification. An instance of a JVM is an implementation running in a process that executes a
computer program compiled into Java bytecode.
Java Runtime Environment (JRE) is a software package that contains what is required to run a
Java program. It includes a Java Virtual Machine implementation together with an
implementation of the Java Class Library. The Oracle Corporation, which owns the Java
trademark, distributes a Java Runtime environment with their Java Virtual Machine called
HotSpot.
Java Development Kit (JDK) is a superset of a JRE and contains tools for Java programmers,
e.g. a java c compiler. The Java Development Kit is provided free of charge either by Oracle
Corporation directly, or by the OpenJDK open source project, which is governed by Oracle.
A Java virtual machine (JVM) is an abstract computing machine that enables a computer to
run a Java program. There are three notions of the JVM: specification, implementation, and
instance. The specification is a document that formally describes what is required of a JVM
implementation. Having a single specification ensures all implementations are interoperable. A
JVM implementation is a computer program that meets the requirements of the JVM
specification. An instance of a JVM is an implementation running in a process that executes a
computer program compiled into Java bytecode.
Java Runtime Environment (JRE) is a software package that contains what is required to run a
Java program. It includes a Java Virtual Machine implementation together with an
implementation of the Java Class Library. The Oracle Corporation, which owns the Java
trademark, distributes a Java Runtime environment with their Java Virtual Machine called Hot
Spot.
Java Development Kit (JDK) is a superset of a JRE and contains tools for Java programmers,
e.g. a java c compiler. The Java Development Kit is provided free of charge either by Oracle
Corporation directly, or by the Open JDK open source project, which is governed by Oracle.

JVM specification


The Java virtual machine is an abstract (virtual) computer defined by a specification. This
specification omits implementation details that are not essential to ensure interoperability: the
memory layout of run-time data areas, the garbage-collection algorithm used, and any internal
optimization of the Java virtual machine instructions (their translation into machine code). The
main reason for this omission is to not unnecessarily constrain implementers. Any Java
application can be run only inside some concrete implementation of the abstract specification of
the Java virtual machine.

, We intend that this specification should sufficiently document the Java Virtual Machine to make
possible compatible clean-room implementations. Oracle provides tests that verify the proper
operation of implementations of the Java Virtual Machine.



VM (Java Virtual Machine) is an abstract machine. It is a specification that provides runtime
environment in which java bytecode can be executed.

JVMs are available for many hardware and software platforms




java
Java is a programming language and a platform.
Java is a high level, robust, secured and object-oriented programming language.
Platform: Any hardware or software environment in which a program runs, is known as a platform.
Since Java has its own runtime environment (JRE) and API, it is called platform.

Java Example

class Simple{ public static void
main(String args[]){
System.out.println("Hello Java");
}
}
Applications of java
There are many devices where java is currently used. Some of them are as follows:

1. Desktop Applications such as acrobat reader, media player, antivirus etc.
2. Web Applications such as irctc.co.in, javatpoint.com etc.
3. Enterprise Applications such as banking applications.
4. Mobile