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The Decorator Pattern Decorators in Java I/O classes

The Decorator Pattern Decorators in Java I/O classes. Decorator Pattern context. You want to attach additional functionality to an (existing) class dynamically… …without having to resort to sub-classing the existing class We don’t want a class explosion

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The Decorator Pattern Decorators in Java I/O classes

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  1. The Decorator PatternDecorators in Java I/O classes SE-2811 Dr. Mark L. Hornick

  2. Decorator Pattern context • You want to attach additional functionality to an (existing) class dynamically… • …without having to resort to sub-classing the existing class • We don’t want a class explosion • We want to allow classes to be easily “extended” to incorporate new behavior without modifying existing code.

  3. + doMoreStuff() SE-2811 Dr. Mark L. Hornick

  4. How are decorators useful? • Decorators have the same super-type as the objects they decorate. • Why is this useful? • One or more decorators can be used to wrap an object. • Why is this useful?

  5. The java.io package contains dozens of classes OutputStream, FileOutputStream, PipedOutputStream, DataOutputStream, ObjectOutputStream, PrintStream, PrintWriter, … Understanding the associations between them just by reading the Javadoc API is difficult SE-2811 Dr. Mark L. Hornick

  6. Knowing that the input stream classes are based on the Decorator pattern can make things easier <<deprecated>> SE-2811 Dr. Mark L. Hornick

  7. The Decorator pattern applied to output streams Only for error propagation in my Java version SE-2811 Dr. Mark L. Hornick

  8. You can create custom stream decorators by extending FilterOutputStream and FilterInputStream • Exercise SE-2811 Dr. Mark L. Hornick

  9. Comparison of Decorator with Strategy SE-2811 Dr. Mark L. Hornick

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