The Java Language Environment

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4.3 Robust

Java is intended for developing software that must be robust, highly reliable, and secure, in a variety of ways. There's strong emphasis on early checking for possible problems, as well as later dynamic (run-time) checking, to eliminate error-prone situations.

4.3.1 Strict Compile-Time and Run-Time Checking

The Java compiler employs extensive and stringent compile-time checking so that syntax-related errors can be detected early, before a program is deployed.

One of the advantages of a strongly typed language (like C++) is that it allows extensive compile-time checking, so bugs can be found early. Unfortunately, C++ inherits a number of loopholes in its compile-time checking from C. Unfortunately, C++ and C are relatively lax, most notably in the area of method or function declarations. Java imposes much more stringent requirements on the developer: Java requires explicit declarations and does not support C-style implicit declarations.

Many of the stringent compile-time checks at the Java compiler level are carried over to the run time, both to check consistency at run time, and to provide greater flexibility. The linker understands the type system and repeats many of the type checks done by the compiler, to guard against version mismatch problems.

The single biggest difference between Java and C or C++ is that Java's memory model eliminates the possibility of overwriting memory and corrupting data. Instead of pointer arithmetic, Java has true arrays and strings, which means that the interpreter can check array and string indexes. In addition, a programmer can't write code that turns an arbitrary integer into an object reference by casting.

While Java doesn't pretend to completely remove the software quality assurance problem, removal of entire classes of programming errors considerably eases the job of testing and quality assurance.

Copyright © 1997 Sun Microsystems, Inc. All Rights Reserved.
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