Exceptions in Java

An Exception is an event that breaks up the normal flow of the program's instructions during the program execution.

Throwable is the parent class for Exception and Error classes.

There are two sub-types in Exception class.One is,Runtime/Unchecked Exceptions and second is,Checked Exceptions.

A simple example

Java Virtual Machine (JVM)

The heart of the Java Platform is the concept of a 'virtual machine' that executes Java bytecode programs. This bytecode is the same, no matter what hardware or operating system the program is running under. There is a JIT (Just In Time) compiler within the Java Virtual Machine, or JVM. The JIT compiler translates the Java bytecode into native processor instructions at run-time and caches the native code in memory during execution.

The Java virtual machine is called "virtual" because it is an abstract computer defined by a specification. To run a Java program, you need a concrete implementation of the abstract specification.


Whenever a Java application starts, instance of JVM is created. JVM instance starts running the application by invoking main() method of some initial class.
Sun has claimed there are over 4.5 billion JVM enabled devices.

JSE Code Names

Java is everywhere.One can't imagine the cybernetic without Java.

It was originally called 'oak' later renamed to 'Java' in 1995.

JSE code names:

VERSION     CODE NAME       RELEASE DATE

------------     -------------------       -------------------------

JDK 1.1.4          Sparkler                  Sept 12, 1997

JDK 1.1.5          Pumpkin                  Dec 3, 1997

JDK 1.1.6          Abigail                     April 24, 1998

JDK 1.1.7          Brutus                     Sept 28, 1998

JDK 1.1.8          Chelsea                  April 8, 1999

J2SE 1.2            Playground             Dec 4, 1998

J2SE 1.2.1         (none)                    March 30, 1999

J2SE 1.2.2         Cricket                  July 8, 1999

J2SE 1.3            Kestrel                   May 8, 2000

J2SE 1.3.1         Ladybird                May 17, 2001

J2SE 1.4.0         Merlin                    Feb 13, 2002

J2SE 1.4.1         Hopper                  Sept 16, 2002

J2SE 1.4.2         Mantis                   June 26, 2003

J2SE 5.0 (1.5.0) Tiger                     Sept 29, 2004

       

J2SE 6.0            Mustang                (December 11, 2006)

J2SE 7.0            Dolphin