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Java and Platform Independency
Fareez Ahamed K.N.
[email protected]
Necessity is the mother of invention. Computer languages are not
an exception to this
rule. However, there are as many as 1600 different computer
languages as they say. Did
all these languages have necessities? Yes. But the importance of
the necessities differ. At
the least it had a necessity to satisfy its own designer. When a
language satisfies a big
need of numerous people, it remains, others wash away or limited
to particular
community. Java is one such language which was designed for
something and outgrown
into something invincible.
C++ was almost a perfect object oriented language. So Javas
objective is not a more
perfect OO Language. The issue that caused Java to originate is
the variety of
microprocessors that started to emerge at that time. Previous
languages were platform
specific. For each platform you have to code a little different
from the others. Javawanted to address this problem. Green team of
Sun Microsystems wanted to create Java
as a platform independent language. By doing so, Java can
incorporate itself into any
embedded system, making the development of embedded system easy
and portable as
well.
But is that possible? Till then the most successful languages
were using compiler to
convert them into object codes that are executable in a
particular platform. So to make
platform independency possible, they have to change this
methodology itself and they
indeed did that to achieve platform independency which is why we
call Java a technology
rather than a language.
Java is compiled and interpreted. It may sound strange. Till the
advent of Java, a
language is either compiled or interpreted but not both. Why
this new method was
brought in? A variety of microprocessors started to emerge and
each one had its own
machine language. Moreover they had different length of
registers to store the data as
well. If you compile your program into a particular machine
language it will not be
supported by other machines. So the green team decided to
compile Java programs into a
common machine language named Bytecode. Bytecode cannot be run
by the
microprocessors directly as no microprocessor knows that
language. Hence we need an
interpreter to interpret Bytecode into the local machine
language. They brought the
concept of virtual machine to achieve this. Java Virtual Machine
is a system software that
can understand the bytecode and interpret it to the lower level
machine. Responsibilitiesof the JVM are a lot more than an
interpreter which is out of scope of over topic.
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Fig 1. Compile and Run Methodology
The above picture represents the traditional compile and run
technique. There are two
platforms A and B ( Call it Pulse and Sawtooth ). An application
which is compiled for
Platform A cannot fit the environment of Platform B. Thus its
not platform independent,
and you have to adjust your program for the new Platform.
Fig 2. Java's Methodology
Java overcomes the problem with the above model. Java
applications are not compiled to
any specific platform. They are compiled to the Bytecode which
will be interpreted by
JVM to the underlying platform. One more thing to notice is,
JVMs have to be
implemented for each platform to run Bytecode on that platform.
This indeed is an issue.
But Sun Microsystems made the Java Virtual Machine Specification
available to
everyone with which the JVM can be implemented to any platform
easily. JVM
Specification and Java language is designed simpler in order to
make the JVM
implementation simpler. It can be implemented to a minimum size
of 680 KB! So that it
can run on smaller chips and cell phones.
When Java came into picture, internet has started to spread
tremendously. Internet is a
network of different platforms, so Java being platform
independent found itself easy to
become the prime technology for web.
This alone is not the success of Java. Though C++ has all the
object oriented features,
Java wanted to make it simple and unambiguous. It removed all
the confusing,
unambiguous and non-productive features from C++, making it the
simplest
implementation of best OO features.
