features of java

• 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.