SwingSlides - JAVA INTERMEDIATE TOPICS Part I Part II Part...

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J AVA INTERMEDIATE TOPICS Part I Exceptions and Collections Part II Threads Part III Swing
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P ART I E XCEPTIONS AND C OLLECTIONS Exceptions and exception handling What are exceptions? When should you use exceptions? Details How are exceptions generated (thrown)? How are exceptions handled (caught)? Runtime exceptions vs. other exceptions. Collections What is a collection? java.util.Collection interface Iterators java.util.Iterator interface Iterator pattern Decoupling of data structure and iteration logic
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W HAT ARE EXCEPTIONS ? Exceptions are a mechanism for handling “exceptional” situations which can occur at runtime. Many languages provide exceptions. Terminology: code where something unexpected happens “throws” an exception code which handles the exceptional situation “catches” the exception – this code is called an exception handler
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W HEN ARE EXCEPTIONS APPROPRIATE ? Exceptions are appropriate to use to signal to a caller a problematic situation which cannot be handled locally. Example: Consider a file reading component which is used both by an interactive UI and a batch processing component. If the file reading component has a problem (“disk is full”), can it decide locally how to respond? No. It is up to the client to decide how to react. The UI may notify its human user. The batch processor may log the problem, and skip processing of this file.
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W HEN ARE EXCEPTIONS NOT APPROPRIATE ? It is not appropriate to use the exception mechanism when an exceptional situation can be handled locally. It is not appropriate to use the exception mechanism in dealing with situations which are not exceptional. If a particular situation is expected, it should be explicitly checked for. For example, if a user supplies the name of a file to be read, it is better to check for existence of the file rather than to attempt to read and rely on a thrown exception to give notice if the file doesn’t exist.
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H OW ARE EXCEPTIONS GENERATED ? An exception is an object An exception must derive from the java.lang.Exception class Detour into inheritance and typing…
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T YPES AND SUBTYPES Every class in Java defines a type. Every interface in Java defines a type. Types are arranged into a hierarchy: classes can extend classes; interfaces can extends interfaces; classes can implement interfaces. Every class except Object has a parent class (which is Object if no other parent is given): every other class has exactly one parent.
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H IERARCHY FOR E XCEPTIONS ( PARTIAL ) Object Throwable Error LinkageError ThreadDeath VirtualMachineError Exception IOException FileNotFoundException MalformedURLException RuntimeException IndexOutOfBoundsException NullPointerException
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S IGNIFICANCE OF HIERARCHY The type hierarchy is significant, not only for exceptions, but for typing in Java more generally. A variable declared to be of a given type can be
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This document was uploaded on 11/03/2011 for the course CSE 116 at SUNY Buffalo.

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SwingSlides - JAVA INTERMEDIATE TOPICS Part I Part II Part...

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