Computer World. Матросова Т.А. - 39 стр.

UptoLike

ВУЗ: 

УлГТУ | Ульяновск

Составители: 

Рубрика: 

38
Exercise 4. Write an abstract of the text.
TEXT 2
Look up the following words and word combinations in a dictionary:
portability, source program, timing, remote target, facilities, pointer, arbitrary
pointer address, sophisticate d, single thre ad, multithreading, embe dde d syste ms,
timing constrains, net applets, target hardware.
Translate the text orally. Write an abstract of the text.
Java is a high-level language with which to write programs that can execute on a
variety of platforms. So are C, C++, Fortran and Cobol, among many others. So the
concept of a portable execution vehicle is not new. Why, then, has the emergence of
Java been trumpeted so widely in the technical and popular press?
Why is Java different from other languages?
Part of Java's novelty arises from its new approach to portability. In previous
High-level languages, the portable element was the source program. Once the source
program is c ompiled into ex ecutable form for a spec ific instruc tion set arc hitecture
(ISA) and bound to a library of hardware-dependent I/O, timing and related operating
system (OS) services, portability is lost. The resultant executable form of the program
runs only on platforms having that specific ISA and OS. Thus, if a program is to run
on several different platforms, it has to be recompiled and relinked for each platform.
And if a program is sent to a remote target for execution, the sender must know in
advance the exact details of the target to be able to send the correct version.
With Java, source statements can be compiled into machine-independent,
«virtual instructions» that are interpreted at execution time. Ideally, the same virtual
code runs in the same way on any platform for which there is an interpreter and OS
that can provide that interpreter with certain multithreading, file, graphical, and
similar support services. With portability moved to the executable form of the
program, the same code can be sent over the net to be run without prior knowledge of
the hardware characteristics of the target. Executable programs in the Java world are
universal.
In principle, portability could have been achieved in the С or C++ world by
sending the source program over the net and then having the compilation and linkage
done as a pre-step to execution. However, this approach would require that the target
system have sufficient CPU speed and disk capacity to run the sophisticated
compilers and linkers required. In the future, network platforms may not have the
facilities to run even a simple compiler.
Is that all?
Java is not just a new concept in portability. The Java language evolved from С
and C++ by locating and eliminating many of the major sources of program error and
instability. For example, С has an element known-as a pointer that is supposed to

Страницы