Anirban%20De

1
Exception Mechanisms

• Anirban De
• Jeffrey Harry
• Yves Lepouchard
• Peixin Li
• Pinchao Lu

2
Why we should care about exceptions

• Ariane 5 Maiden Flight
• Computer automation is everywhere
• in your daily life
• in critical systems
• Exception handling
• Our project deals with
• Java
• THE HOT programming language

HOT
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Java Exception Handling

• Exceptions are objects
• Multilevel Model
• Termination Model

STOP!
Server
END
Try Workers Finally Cleaners Catch
Handlers
Check
Receive
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Exception Handling Enhancements
RESCUE-RETRY CONSTRUCT
/ Attempt to transmit a message 100 times and
set tx_successful / Public void
transmit_message(String message) if
(tx_failures lt 100) attempt_transmission(messag
e) tx_successful true else tx_successful
false / rescue tx_failures
tx_failures 1 retry /
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Exception Handling Enhancements

• Rescue-Retry added using JJTree and JavaCC
• JJTree is a bottom-up Parse Tree Builder
• JavaCC uses the output of JJTree to generate the
  Lexer/Parser
• Generates a top-down, recursive descent parser
• Partial EBNF Notation for Rescue-Retry
• void MethodBodyBlock( )
• RequireClause( ) ( BlockStatement( ) )
  EnsureClause( ) RescueClause( )
• void RescueClause( )
• ltRESCUEgt (RescueCatch( ) )
  ltASSRN_ENDgt
• void RescueCatch( )
• ( "catch" "(" FormalParameter() ")" )? "" (
  BlockStatement() RetryStatement() )

6
Evaluation

• Things we sort of already knew...

• Java is slow, more Java is slower.

• Given a Java program, adding more Java is going
  to make it larger.

We didnt know how much slower/larger...
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Evaluation
How much slower is Jass?
How much larger?
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Conclusion
Its a hog, its slow, its big...
Value inside (Safe, reusable error-free code.)
BUT...
9
Java Exception Handling