Sunday, June 29, 2008

Java Featutes

Java Featutes
  • Platform Independence
    • The Write-Once-Run-Anywhere ideal has not been achieved (tuning for different platforms usually required), but closer than with other languages.

  • Object Oriented
    • Object oriented throughout - no coding outside of class definitions, including main().
    • An extensive class library available in the core language packages.

  • Compiler/Interpreter Combo
    • Code is compiled to bytecodes that are interpreted by a Java virtual machines (JVM) .
    • This provides portability to any machine for which a virtual machine has been written.
    • The two steps of compilation and interpretation allow for extensive code checking and improved security.

  • Robust
    • Exception handling built-in, strong type checking (that is, all data must be declared an explicit type), local variables must be initialized.

  • Several dangerous features of C & C++ eliminated:
    • No memory pointers
    • No preprocessor
    • Array index limit checking

  • Automatic Memory Management
    • Automatic garbage collection - memory management handled by JVM.

  • Security
    • No memory pointers
    • Programs runs inside the virtual machine sandbox.
    • Array index limit checking
    • Code pathologies reduced by
      • bytecode verifier - checks classes after loading
      • class loader - confines objects to unique namespaces. Prevents loading a hacked "java.lang.SecurityManager" class, for example.
      • security manager - determines what resources a class can access such as reading and writing to the local disk.

  • Dynamic Binding
    • The linking of data and methods to where they are located, is done at run-time.
    • New classes can be loaded while a program is running. Linking is done on the fly.
    • Even if libraries are recompiled, there is no need to recompile code that uses classes in those libraries.

      This differs from C++, which uses static binding. This can result in fragile classes for cases where linked code is changed and memory pointers then point to the wrong addresses.

  • Good Performance
    • Interpretation of bytecodes slowed performance in early versions, but advanced virtual machines with adaptive and just-in-time compilation and other techniques now typically provide performance up to 50% to 100% the speed of C++ programs.

  • Threading
    • Lightweight processes, called threads, can easily be spun off to perform multiprocessing.
    • Can take advantage of multiprocessors where available
    • Great for multimedia displays.

  • Built-in Networking
    • Java was designed with networking in mind and comes with many classes to develop sophisticated Internet communications.
Features such as eliminating memory pointers and by checking array limits greatly help to remove program bugs. The garbage collector relieves programmers of the big job of memory management. These and the other features can lead to a big speedup in program development compared to C/C++ programming.
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