The Java(TM) Language - An Overview

The JavaTM Language - An Overview

2000. 3. 13.

Kwang Shin OhDept. of Research & Development

http://[email protected]

Copyright 2000 © Kwang Shin Oh

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Http://raytrust.pe.kr

Introduction Java Programming language

designed to solve a number of problems in modern programming practice

started as a part of a larger project to develop advanced software for consumer electronics

to devices are small, reliable, portable, distributed, real-time embedded systems

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Java Java is a simple, object-oriented,

distributed, interpreted, robust, secure, architecture neutral, portable, high-performance, multithreaded, and dynamic language.

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Java – Simple without a lot of esoteric training

and which leveraged today’s standard practice

designed as closely to C++ as possible in order to make the system more comprehensible

omits many rarely used, poorly understood, confusing features of C++

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Java – Simple omitted features

operator overloading(although the Java language does have method overloading)

multiple inheritance extensive automatic coercions

added auto garbage collection simplifying the task of Java

Programming making the system somewhat more

complicated

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Java – Simple complexity in many C and C++ applicat

ions storage management : the allocation and

freeing of memory automatic garbage collection benefits

makes the programming task easier dramatically cuts down on bugs

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Java – Simple small

enable the construction of software that can run stand-alone in small machines

the size of the basic interpreter and class support about 40K bytes

basic standard libraries and thread support additional 175K bytes

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Java – Object Oriented Object Oriented design

technique that focuses design on the data(=objects) and on the interfaces to it

OO design is very powerful facilitates the clean definition of interface makes it possible to provide reusable soft

ware

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Java – Object Oriented analogy with carpentry

“object-oriented” carpenter mostly concerned with the chair he was buildi

ng secondarily with the tools used to make it

“non-object-oriented” carpenter think primarily of his tools

mechanism for defining how modules “plug and play”

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Java – Distributed extensive library of routines

coping easily with TCP/IP protocols like HTTP and FTP

open and access objects across the net via URLs

same when accessing a local file system

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Java – Robust must be reliable in a variety of ways a lot of emphasis

early checking for possible problems later dynamic(runtime) checking eliminating situations that are error prone

advantages of a strongly typed language(like C++) allows extensive compile-time checking s

o bugs can be found early

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Java – Robust C++ inherits a number of

loopholes in compile-time checking from C relatively lax(particularly method /

procedure declarations) in Java

require declarations and do not support C-style implicit declarations

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Java – Robust single biggest difference between

Java and C/C++ java has a pointer model that

eliminates the possibility of overwriting memory and corrupting data

not possible to turn an arbitrary integer into a pointer by casting

you don’t have to worry about freeing or corrupting memory

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Java – Secure java enables the construction of virus-

free, tamper-free systems authentication technique are based on

public-key encryption changes to the semantics of pointers

make it impossible for applications to forge access to data structures to access private data in objects that they

do have access to closes the door on most activities of

viruses

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Java – Architecture Neutral designed to support applications on network

s variety of systems with a variety of CPU and oper

ating system architectures to enable a Java application to execute anyw

here on the network the compiler generates an architecture neutral o

bject file format the compiled code is executable on many proces

sors, given the presence of the Java runtime system

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Java – Architecture Neutral useful not only for networks but also fo

r single system software distribution makes the production of software that

runs on all platforms Java compiler generating bytecode inst

ructions easy to interpret on any machine easily translated into native machine code

on the fly

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Java – Portable being architecture neutral is a big

chunk of being portable but there’s more to it than that

unlike C and C++, there are no “implementation dependent” aspects of the specification

sizes of the primitive data types are specified, as is the behavior of arithmetic on them(examples are int, float)

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Java – Interpreted Java interpreter

execute Java bytecodes directly on any machine to which the interpreter has been ported

linking is a more incremental and lightweight process so, the development process can be muc

h more rapid and exploratory

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Java – High Performance bytecode format was designed with

generating machine codes in mind so, the actual process of generating

machine code is generally simple Reasonably good code is produced

does automatic register allocation and the compiler does some optimization when it produces the bytecodes

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Java – High Performance in interpreted code

about 300,00 method calls per second on an Sun Microsystems SPARCStation 1

0 performance of bytecodes converted to

machine code almost indistinguishable from native C or

C++

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Java – Multithreaded there are many things going on at the same

time in the world around us multithreading

a way of building applications with multiple threads

Java has a sophisticated set of synchronization primitives that are based on the widely used monitor and condition variable paradigm that was introduced by C.A.R.Hoare

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Java – Dynamic In a number of ways, Java is a more

dynamic language than C or C++ for example, one major problem with

using C++ in a production environment is a side-effect of the way that code is always implemented

company A produces a class library(a library of plug and

play components)

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Java – Dynamic company B

buys it and uses it tin their product company A

changes its library and distributes a new release company B

will almost certainly have to recompile and redistribute their own software

problems can result when the end user gets A and B’s software independently (say A is an OS vendor and B is an application vendor)

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Java – Dynamic A distributes an upgrade to its libraries

then all of the software from B will break it is possible to avoid this problem in C

++, but it is extraordinarily difficult it effectively means not using any of the l

anguage’s OO features directly

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Java – Dynamic by making these interconnections

between modules later Java completely avoids these problems makes the use of the object-oriented

paradigm much more straightforward libraries can freely add new

methods and instance variables without any effect on their clients

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Java – Dynamic Java uses interfaces

a concept borrowed from Objective C which is similar to a class

simply a specification of a set of methods that an object responds to

not include any instance variables or implementations

can be multiply-inherited(unlike classes) and they can be used in a more flexible way than the usual rigid class inheritance structure

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Java – Dynamic classes have a runtime representation

there is a class named Class, instances of which contain runtime class definitions

in a C or C++ program have a pointer to an object don’t know that type of object it is there is no way to find out

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Java – Dynamic in Java

finding out based on the runtime type information is straightforward

because casts are checked at both compile-time and runtime trust a cast in Java on the other

hand in C and C++ compiler just trusts that you’re

doing the right thing

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Java – Dynamic possible to look up the definition

of a class given a string containing its name

this means that you can compute a data type name and have it easily dynamically-linked into the running system

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Summary The Java language provides a

powerful addition to the tools that programmers have at their disposal

Java makes programming easier it is object-oriented has automatic garbage collection compiled Java code is architecture-

neutral Java applications are ideal for a

diverse environment like the Internet

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Reference Sun Microsystems

The JAVATM Language:An Overview

Technology

The Java(TM) Language - An Overview