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The DiffUtils library for computing diffs, applying patches, generationg side-by-side view in Java.
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/*
 * ====================================================================
 *
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 1999-2003 The Apache Software Foundation.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
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 *    distribution.
 *
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 *    any, must include the following acknowledgement:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgement may appear in the software itself,
 *    if and wherever such third-party acknowledgements normally appear.
 *
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 * ====================================================================
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 * This software consists of voluntary contributions made by many
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 * .
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package difflib.myers;

/**
 * A node in a diffpath.
 *
 * @version $Revision: 69 $ $Date: 2003-10-13 11:00:44 +0300 (Пнд, 13 Окт 2003) $
 * @author Juanco Anez
 *
 * @see DiffNode
 * @see Snake
 *
 */
public abstract class PathNode {
    /** Position in the original sequence. */
    public final int i;
    /** Position in the revised sequence. */
    public final int j;
    /** The previous node in the path. */
    public final PathNode prev;
    
    /**
     * Concatenates a new path node with an existing diffpath.
     * @param i The position in the original sequence for the new node.
     * @param j The position in the revised sequence for the new node.
     * @param prev The previous node in the path.
     */
    public PathNode(int i, int j, PathNode prev) {
        this.i = i;
        this.j = j;
        this.prev = prev;
    }
    
    /**
     * Is this node a {@link Snake Snake node}?
     * @return true if this is a {@link Snake Snake node}
     */
    public abstract boolean isSnake();
    
    /**
     * Is this a bootstrap node?
     * 
     * In bottstrap nodes one of the two corrdinates is
     * less than zero.
     * @return tru if this is a bootstrap node.
     */
    public boolean isBootstrap() {
        return i < 0 || j < 0;
    }
    
    /**
     * Skips sequences of {@link DiffNode DiffNodes} until a
     * {@link Snake} or bootstrap node is found, or the end
     * of the path is reached.
     * @return The next first {@link Snake} or bootstrap node in the path, or
     * null
     * if none found.
     */
    public final PathNode previousSnake() {
        if (isBootstrap())
            return null;
        if (!isSnake() && prev != null)
            return prev.previousSnake();
        return this;
    }
    
    /**
     * {@inheritDoc}
     */
    public String toString() {
        StringBuffer buf = new StringBuffer("[");
        PathNode node = this;
        while (node != null) {
            buf.append("(");
            buf.append(Integer.toString(node.i));
            buf.append(",");
            buf.append(Integer.toString(node.j));
            buf.append(")");
            node = node.prev;
        }
        buf.append("]");
        return buf.toString();
    }
}