DifferenceReader

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tribble.text
Class DifferenceReader

java.lang.Object
  tribble.text.DifferenceReader

public class DifferenceReader
extends java.lang.Object

Text difference generator (INCOMPLETE).

This class takes two input text streams and generates the differences between them. Each input stream is composed of lines of text. The difference generator determines the differences between the first input stream, called the previous (or old) input, and the second input stream, called the current (or new) input.

The output of the generator is a sequence of deltas. Each delta specifies either a keep, delete, or insert command for a specific text line number. Applying the sequence of deltas to text lines in the old input stream produces the text lines of the new input stream.

Delta commands:

keep (CMD_KEEP): A text line from the old input stream is to be kept and copied as is to the output stream.
delete (CMD_DELETE): A text line from the old input stream is to be removed and not written to the output stream.
insert (CMD_INSERT): A text line from the new input stream is to be inserted into the output stream.
end (CMD_END): Both the old and new input streams have been read completely, and there are no more delta commands to be generated.

The difference generator operates by using a look-ahead window of a certain number of text lines. By default, this window contains 200 lines of text, but this size can be changed if desired.

Usage

First, the previous (old) and current (new) input streams are initialized.

    LineNumberReader    prev;
    LineNumberReader    curr;

    prev = new LineNumberReader(...);
    curr = new LineNumberReader(...);

Next, a difference generator is created and initialized.

    DifferenceReader    difr;

    difr = new DifferenceReader(prev, curr);

The size of the difference window can be changed if so desired.

    difr.setWindowSize(400);

At this point, the sequence of deltas between the old and new input streams can be generated.

    int     cmd;

    do
    {
        String  text;

        // Get the next delta command
        cmd = difr.getDelta();

        switch (cmd)
        {
        case DifferenceReader.CMD_KEEP:
            // Keep (copy) a line from the old stream
            text = difr.getDeltaText();
            ...
            break;

        case DifferenceReader.CMD_DELETE:
            // Delete a line from the old stream
            ...
            break;

        case DifferenceReader.CMD_INSERT:
            // Insert a line from the new stream
            text = difr.getDeltaText();
            ...
            break;
        }

    } while (cmd != DifferenceReader.CMD_END);

A CMD_END command is generated when both the old and new input streams have been read completely.

After all of the difference deltas have been generated, the difference generator can be closed.

    difr.close();

Acknowledgments

This code was derived from an original algortihm devised by David R. Tribble.

Since:: 2003-09-06
Version:: $Revision: 1.2 $ $Date: 2004/10/03 18:35:26 $
Author:: David R. Tribble (david@tribble.com).
Copyright Š2003,2004 by David R. Tribble, all rights reserved.
Permission is granted to freely use and distribute this source code provided that the original copyright and authorship notices remain intact.

Field Summary
`static short`	`CMD_DELETE` Delta command: Delete a line from the old input stream.
`static short`	`CMD_END` Delta command: End of both input streams.
`static short`	`CMD_INSERT` Delta command: Insert a line from the new input stream.
`static short`	`CMD_KEEP` Delta command: Keep a line from the old input stream.
`static int`	`DFL_WINDOW_LEN` Default text line window size (200).

Constructor Summary
`DifferenceReader(java.io.Reader prev, java.io.Reader curr)` Constructor.

Method Summary
`void`	`close()` Close this difference generator.
`protected void`	`finalize()` Finalization.
`int`	`getDelta()` Generate the next difference delta command.
`int`	`getDeltaLineNumber()` Retrieve the line number of the text line for the last difference delta command generated.
`java.lang.String`	`getDeltaText()` Retrieve the text line for the last difference delta command generated.
`static void`	`main(java.lang.String[] args)` Determine the difference between two text files.
`protected tribble.text.DiffLine`	`readLine(java.io.LineNumberReader in)`
`void`	`setWindowSize(int len)` Establish the size of the text line difference window.

Methods inherited from class java.lang.Object

clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DFL_WINDOW_LEN

public static final int DFL_WINDOW_LEN

Default text line window size (200).

See Also:: Constant Field Values

CMD_END

public static final short CMD_END

Delta command: End of both input streams.

See Also:: Constant Field Values

CMD_KEEP

public static final short CMD_KEEP

Delta command: Keep a line from the old input stream.

See Also:: Constant Field Values

CMD_DELETE

public static final short CMD_DELETE

Delta command: Delete a line from the old input stream.

See Also:: Constant Field Values

CMD_INSERT

public static final short CMD_INSERT

Delta command: Insert a line from the new input stream.

See Also:: Constant Field Values

Constructor Detail