Computer Science 111 Fundamentals of Computer Programming I

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Computer Science 111Fundamentals of Computer
Programming I

• Introduction to Java exception handling

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News Alert
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Run-time errors

• There are certain kinds of errors that the
  compiler can not detect
• First of all there are logic errors we simply
  make a mistake in the logic of our code. The
  compiler doesnt know how to play Blackjack.
• Then there are run-time errors - situations
  arise during execution that we didnt anticipate
  and the compiler had no way to anticipate.
• User inputs a zero for a divisor.
• We try to access an array element using a
  subscript that is not within range
• Etc.
• What happens?

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Run-time error example
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The Black screen of death!
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Java Exceptions

• When a run-time error occurs, Java throws an
  exception.
• We can write sections of code that catch the
  exception if it occurs and deal with it within
  the program.
• Some parts of our Java code are required to
  anticipate and deal with errors this way.
• An example would be when we are trying to use a
  file that may or may not exist.

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Partial Class Hierarchy
Throwable
Exception
Error
RuntimeException
IOException
ArithmeticException
IndexOutOfBoundsException
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Java Documentation
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try-catch statements

• With try-catch statements
• There is a try block that contains the code we
  want to execute.
• There is a catch block that specifies the
  exception type that we want to handle and the
  code to execute if the error occurs.

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No black screen of death!
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But, will they be here tomorrow?