To better understand how Java is robust, consider two of the main reasons for program
failure: memory management mistakes and mishandled exceptional conditions (that is,
run-time errors). Memory management can be a difficult, tedious task in traditional
programming environments. For example, in C/C++, the programmer must manually allocate
and free all dynamic memory. This sometimes leads to problems, because programmers will
either forget to free memory that has been previously allocated or, worse, try to free some
memory that another part of their code is still using. Java virtually eliminates these problems
by managing memory allocation and deallocation for you. (In fact, deallocation is completely
automatic, because Java provides garbage collection for unused objects.) Exceptional conditions
in traditional environments often arise in situations such as division by zero or "file not found,"
and they must be managed with clumsy and hard-to-read constructs. Java helps in this area
by providing object-oriented exception handling. In a well-written Java program, all run-time
errors can--and should--be managed by your program.
Multithreaded
Java was designed to meet the real-world requirement of creating interactive, networked
programs. To accomplish this, Java supports multithreaded programming, which allows
you to write programs that do many things simultaneously. The Java run-time system
comes with an elegant yet sophisticated solution for multiprocess synchronization that
enables you to construct smoothly running interactive systems. Java's easy-to-use approach
to multithreading allows you to think about the specific behavior of your program, not the
multitasking subsystem.
Architecture-Neutral
A central issue for the Java designers was that of code longevity and portability. One of the
main problems facing programmers is that no guarantee exists that if you write a program
today, it will run tomorrow--even on the same machine. Operating system upgrades,
processor upgrades, and changes in core system resources can all combine to make a
program malfunction. The Java designers made several hard decisions in the Java language
and the Java Virtual Machine in an attempt to alter this situation. Their goal was "write
once; run anywhere, any time, forever." To a great extent, this goal was accomplished.
Interpreted and High Performance
As described earlier, Java enables the creation of cross-platform programs by compiling
into an intermediate representation called Java bytecode. This code can be executed on
any system that implements the Java Virtual Machine. Most previous attempts at
cross-platform solutions have done so at the expense of performance. As explained earlier,
the Java bytecode was carefully designed so that it would be easy to translate directly into
native machine code for very high performance by using a just-in-time compiler. Java run-time
systems that provide this feature lose none of the benefits of the platform-independent code.
Distributed
Java is designed for the distributed environment of the Internet because it handles TCP/IP
protocols. In fact, accessing a resource using a URL is not much different from accessing a
file. Java also supports Remote Method Invocation (RMI). This feature enables a program to
invoke methods across a network.
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