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C H A P T E R

Introduction

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If I have seen further it is by standing upon the shoulders of Giants.

Sir Isaac Newton

J

AVA is a general purpose, concurrent, class based, object oriented language. It

is designed to be simple enough that many programmers can achieve fluency in

the language. Java is related to C and C++ but is organized rather differently, with

a number of aspects of C and C++ omitted and a few ideas from other languages

included. Java is intended to be a production language, not a research language,

and so, as C. A. R. Hoare suggested in his classic paper on language design, the

design of Java has avoided including new and untested features.

Java is strongly typed. This specification clearly distinguishes between the

compile time errors

 that can and must be detected at compile time, and those that

occur at run time. Compile time normally consists of translating Java programs

into a machine independent byte code representation. Run time activities include

loading and linking of the classes needed to execute a program, optional machine

code generation and dynamic optimization of the program, and actual program

execution.

Java is a relatively high level language, in that details of the machine repre 

sentation are not available through the language. It includes automatic storage

management, typically using a garbage collector, to avoid the safety problems of

explicit deallocation (as in C's

free

 or C++'s

delete

). High performance gar 

bage collected implementations of Java can have bounded pauses to support sys 

tems programming and real time applications. Java does not include any unsafe

constructs, such as array accesses without index checking, since such unsafe con 

structs would cause a program to behave in an unspecified way.

Java is normally compiled to a bytecoded instruction set and binary format

defined in

The Java Virtual Machine Specification

(Addison Wesley, 1996). Most

implementations of Java for general purpose programming will support the addi 

tional packages defined in the series of books under the general title

The Java

Application Programming Interface

 (Addison Wesley).

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