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Input/Output for Histograms
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A useful feature for our histogram classes would be the capability to save histogram data (including bin values, range, titles) to a disk file and conversely to read histogram data from a file and recreate the histogram from this data.

To rebuild an instance of the base class Histogram we would need the bin array, the upper and lower range, the under and over flow values, and also the text information such as the title and axes labels. For the subclasses we would need additional data values as well.

To provide histogram I/O there are several approaches to the class design:

  • Getters/Setters
    Provide get[Field]() and set[Field]() methods in the Histogram class for all of the data fields necessary to save and rebuild the histograms. An application method can then "get" the data from a histogram and write the data to a file. Conversely, an application could read in the data from the file and create a new Histogram object and fill its data fields with the values from the saved histogram using the setter methods or via the arguments of a constructor.

    Demo 1

  • Stream Wrappers
    A variation on the above approach is to create a new class (or classes) whose only job is to write or read a histogram to/from a file. Such a wrapper could use gettter/setter methods if available or, if it has access privileges, directly access the histogram class fields. For example, if the fields are protected, a wrapper in the same package can directly access the fields.

  • Serialized Objects
    The most elegant approach is simply to make the histogram classes Serializable and save the histogram objects to a disk file by writing them to an output object stream. To rebuild the histograms, just open an input object stream to the file and read them in. We discussed in Chapter 9: Java : Object I/O the general techniques for creating and using object streams.

    Demo 2

We demonstrate both the getter/setter and serialized object approaches. The former approach illustrates some useful class design concepts and it also has the advantage that we do not need to modify the Histogram class or its subclasses in any way.

References & Web Resources

Latest update: Nov. 14, 2004

Histogram I/O
Hist I/O - Get/Set
  Demo 1
Hist I/O - Objects
  Demo 2
  Demo 3
Filtering Data
  Demo 4

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