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有关JAVA领域的外文翻译.pdf
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有关JAVA领域的外文翻译.pdf
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原文
Java 2 Micro Edition and the World of Java
1 Introduction
The puter revolution of the 1970s increased the demand for so
phisticated putersoftware to take advantage of the ever-increasing c
apacity of puters to process data.The C programming language bec
ame the linchpin that enabled programmers to buildsoftware that
was just as robust as the puter it ran on.
As the 1980s approached, programmers were witnessing anoth
er spurt in the evolutionof programming language. puter technolog
y advanced beyond the capabilities of the C programming language.
The problem wasn’t new. It occurred previously and caused the
demise of generations of programming languages. The problem was
thatprograms were being too plicated to design, write, and manag
e to keep up with the capabilities of puters. It was around this ti
me that a design concept based on Simula 67 and Smalltalk (from
the late 1960s) moved programming to the next evolutionary step.
This was the period when object-oriented programming (OOP), and
with it a new programming language called C++, took programmer
s by storm.
In 1979, Bjarne Stroustrup of Bell Laboratories in New Jersey
enhanced the C programming language to include object-oriented f
eatures. He called the language C++. (The ++ is the incremental op
erator in the C programming language.) C++ is truly an enhancem
ent of the C programming language, and it began as a preprocesso
r language that was translated into C syntax before the program w
as processed by the piler.
Stroustrup built on the concept of a class (taken from Simula 67
and Smalltalk), from which instances of objects are created. A clas
s contains data members and member functions that define an obj
ect’s data and functionality. He also introduced the concept of in
heritance, which enabled a class to inherit some or all data memb
ers and member functions from one or more other classes—all of
which plements the concepts of object-oriented programming.
By 1988, ANSI officials standardized Stroustrup’s C++ specific
ation.
2 Enter Java
Just as C++ was being the language of choice for building ind
ustrial-strength applications, another growth spurt in the evolution
of programming language was budding, fertilized by the latest disr
uptive technology—the World Wide Web. The Internet had been a
well-kept secret for decades before the National Science Foundation
(who oversaw the Internet) removed barriers that prevented mercia
lization. Until 1991 when it was opened to merce, the Internet was
the almost exclusive domain of government agencies and the acad
emic munity. Once the barrier to mercialization was lifted, the Wor
ld Wide Web—one of several services offered on the Internet— beca
me a virtual munity center where visitors could get free informatio
n about practically anything and browse through thousands of virt
ual stores.
Browsers power the World Wide Web.A browser translates ASCI
I text files written in HTML into an interactive display that can be
interpreted on any machine. As long as the browser is patible wit
h the correct version of HTML and HTTP implementation, any pute
r running the browser can use the same HTML document without
having to modify it for a particular type of puter, which was somet
hing unheard of at the time. Programs written in C or C++ are ma
chine dependent and cannot run on a different
machine unless the program is repiled.
The success of the Internet gave renewed focus to developing a
machine-independent programming language. And the same year t
he Internet was mercialized, five technologists at Sun Microsystems
set out to do just that. James Gosling, Patrick Naughton, ChrisW
arth, Ed Frank, and Mike Sheridan spent 18 months developing th
e programming language they called Oak, which was renamed Java
when this new language made its debut in 1995. Java went thro
ugh numerous iterations between 1991 and 1995, during which ti
me many other technologists at Sun made substantial contribution
s to the language. These included Bill Joy, Arthur van Hoff, Jonat
han Payne, Frank Yelin, and Tim Lindholm.
Although Java is closely associated with the Internet, it was de
veloped as a language for programming software that could be em
bedded into electronic devices regardless of the type of CPU used
by the device. This is known as the EmbeddedJava platform and i
s in continuous use today for closed systems.
The Java team from Sun succeeded in creating a portable prog
ramming language, something that had eluded programmers since
puters were first programmed. Their success, however, was far bey
ond their wildest dreams. The same concept used to make Java pr
ograms portable to electronic devices also could be used to make J
ava programs run on puters running Microsoft Windows, UNIX, an
d Macintosh. Timing was perfect. The Internet/intranet had whette
d corporate America’s appetite for cost-effective, portable programs
that could replace mission-critical applications within the corporat
ion. And Java had proven itself as a programming language used t
o successfully develop machine-independent applications.
3 Java Virtual Machine
Writing Java programs is similar to writing C++ programs in t
hat the programmer writes source code that contains instructions i
nto an editor, or in an integrated development
environment, and then the source code is piled. However, that’s w
here Java and C++
part ways. The piling and linking process of a C++ program results
in an executable
that can be run on an appropriate machine. In contrast, the Java
piler converts Java
source code into bytecode that is executed by the Java Virtual Ma
chine (JVM).
Machine-specific instructions are not included in bytecode. Inst
ead, they already reside in the JVM, which is machine specific. Th
is means that the bytecode might contain fewer instructions that n
eed to be translated than a parable C++ program.
A lthough the Java piler generates bytecode that must be interp
reted by the JVM
at run time, the number of instructions that need translation are
usually minimal and
have already been optimized by the Java piler.
4 Back to the Future: J2ME
Remember that Java began as a programming language to crea
te programs for embedded systems—microputers found in consume
r and industrial products such as those used to control automobil
es and appliances. The development team at Sun worked on Java
in the early 1990s to address the programming needs of the fledgli
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