NYC.ACM:Java

  ============================: TUE.OCT,971021 :============================
|18:26| Java : Programing Language of Web ? . AndrewWright , NEC Res Inst
 Princton NJ .  <wright@research.nj.nec.com>
|18:40| Tek look @ Java : |
 In audience : 3 Java programmers , same C++ . lots C C . Me + 1 APL .
 Object oriented , Type-save . to write general apps & Web applets .
 Java programs run in Browser . Shipped accross net on demand . compiled to
 byte code ( like old Pascal P-code ) . can communicate .  foundation for
 web programs : collaborative editors , newspapers .
Unrelated :
  Javascript : can be embedded in wef pages & interpreted . was originally
   called LiveScript .
  ActiveX : MS framework for downloacing native machine code into browser .
  Offer similar capabilities as Java Applets but unrelated .
 Java as prog lang - advances over C , C++ .
  + Type-safety : run-time value must match compile time type .
      Widget w ;  | w can only hold Widget
     enforced by Static typing & some dynamic checking & typing .
     Bounds chking .  Type ð set of values
      cast m arrat access  - perform runtime chking .
  + Abstraction - aids mngng cmplxity .
     class Point { private int x , y ; void move ( int dx ,dy )  {
  } }
    interface Widget { void move ( int dx ,dy )  ; }
    class Point Impelents Widget { ... }  | implementor of Widget
    class Motion { void translate  ( Widget w ) { .... }  |
     client of Widget
  + Portability
    all programs have defined meaning . EVEN THOSE W ERRORS . ( Error
     behavior all defined . )
    ' write once , run anywhere ' on JavaVirtualMachine .
    use commodity hardware .
  + Garbage Collection
    Drop pointer to object & its gone . automatic resource finalization of
     I/O ports , etc .
    Simplifies interfaces - no ownerhsip tracking - no manual reference
     counts .
    Essential for type-safety .
    Blamed for being really slow .  Sun`s 10 yr old . copying collection
     of good stuff .
  + Exception handling . C++ now has - Code for handling errors can be
      localized .
     Raise exception rather than return status . avoids "forgot to chek
      return status" bugs .
     User code can handle system errors : eg  %0 . array bounds violation .
  May be able to turn off some run time chks .
  Deficienies :
   Abstractions can be broken ,  has 'instanceof '  fn to determine type
    Can access memberf via reflection API
    No guarentee that clients don`t depend on interface implementation .
   Weak module sys . No Package interface . Packages can`t be nested .
  Complex semantics :
   class A { int f( int y ) { .. } . }   | class B
    extend A { ... }
   Has Dynamic inheritance for methods , static for fields .
  Has no mathematicall definition .
   English specification is imprecise . implementers misinterpret .
    ( Standard  ML  is precise )
   Can`t  prove theorums abt language  or programs
  - no parameterized classes . OOP for hetero collections , ~ homogeneous
    orderd   .     No Sort routines in Java Class Lib .
  Bell Labs extension : Pizza  Wadler & Odersky ,
    interface  Ordered
  -  implementations  SLOW .
    2-40 x slower than C . JustInTime Comipler produces native code frm byte
    : 2-10 x slower than C .
    Implementations are slowly improving .
  - No support for other paradigms
    - poor supoort fof procedural or functional programming . no data def
     facility . no convenient way to walk data structures .
 Designing w datatypes :   Std ML example .
  datatype
  either behaviors or datatypes  distributed accross objects .
   [ verb or noun centered ]
Web programs .  Running an applet .
 < applet code="TumbleItem.class" with =    height=  >
  < downlad byte-codes in TumbleItme.class
  Browser MUST guard against malicious applets . can have NO holes .
   [ nuff said ]  run quicken .  access others on your intranet .
   ( down hall have 10Mb cable modem )
  Firewalls don`t  help since still want to run Web .
 Applets run in 'sandbox' - can`t : read or write local disk , communicate w
  other servers , start other programs .
 Current browser Y JVM not robust .
  Depends on type-safety , byte-code verifyer , security of class-loader (
   compler-time & run-time types of linked objs must match )
  Depends on secure library routines : openURL  getFont ( ..\..\*.* )
 Netscape - 95 .   DNS spoofing
 Java written in C .
  ActiveX bigger can of worms .
 Netscape & Explorer have no console showing running applets . ( may remain
  running ) . no audit trails .
   cryptograpy til `9705 .
 Sandboxing too restrictive . Want Digital Certificates . Ok to trust
  applet ? - all or nothing security . applet itself must be secure .
 Static analysis for security
  ( Andrew`s research )  - compile time analysis of info flow .
   info flow graph . eg :  Show applet keeps inside data in , outside out .
 Security is a system wide problem .
 Proof carrying code ( Lee @ CMU ) program comes w machine- chekable proof
  of security properties . proofs .
 If download applet , full access like plug-ins .
 NOT ultimate language but better than C++ .
 Java & Web still young .
|20:20| |20:25|