What is java?
Ø Java
is a programming language expressly designed for use in the distributed environment
of the Internet. It was designed to have the "look and feel" of the
C++ language, but it is simpler to use than C++ and enforces an object-oriented
programming model. Java can be used to create complete applications that may
run on a single computer or be distributed among servers and clients in a
network. It can also be used to build a small application module or applet for
use as part of a Web page. Applets make it possible for a Web page user to
interact with the page.
The major characteristics of Java are:
Ø The
programs you create are portable in a network. (See portability.) Your source
program is compiled into what Java calls bytecode, which can be run anywhere in
a network on a server or client that has a Java virtual machine. The Java
virtual machine interprets the bytecode into code that will run on the real
computer hardware. This means that individual computer platform differences
such as instruction lengths can be recognized and accommodated locally just as
the program is being executed. Platform-specific versions of your program are
no longer needed.
Ø The
code is robust, here meaning that, unlike programs written in C++ and perhaps
some other languages, the Java objects can contain no references to data
external to themselves or other known objects. This ensures that an instruction
cannot contain the address of data storage in another application or in the
operating system itself, either of which would cause the program and perhaps
the operating system itself to terminate or "crash." The Java virtual
machine makes a number of checks on each object to ensure integrity.
Ø Java
is object-oriented, which means that, among other characteristics, an object
can take advantage of being part of a class of objects and inherit code that is
common to the class. Objects are thought of as "nouns" that a user
might relate to rather than the traditional procedural "verbs." A
method can be thought of as one of the object's capabilities or behaviors.
Ø In
addition to being executed at the client rather than the server, a Java applet
has other characteristics designed to make it run fast.
Ø Relative
to C++, Java is easier to learn. (However, it is not a language you'll pick up
in an evening!)
Java was introduced by Sun Microsystems in 1995 and
instantly created a new sense of the interactive possibilities of the Web. Both
of the major Web browsers include a Java virtual machine. Almost all major
operating system developers (IBM, Microsoft, and others) have added Java
compilers as part of their product offerings.
The Java virtual machine includes an optional
just-in-time compiler that dynamically compiles bytecode into executable code
as an alternative to interpreting one bytecode instruction at a time. In many
cases, the dynamic JIT compilation is faster than the virtual machine
interpretation.
JavaScript should not be confused with Java.
JavaScript, which originated at Netscape, is interpreted at a higher level, is
easier to learn than Java, but lacks some of the portability of Java and the
speed of bytecode. Because Java applets will run on almost any operating system
without requiring recompilation and because Java has no operating system-unique
extensions or variations, Java is generally regarded as the most strategic
language in which to develop applications for the Web. (However, JavaScript can
be useful for very small applications that run on the Web client or server.)
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