TextUtilities.java Source code

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Here is the source code for TextUtilities.java

Source

/*
 * TextUtilities.java - Utility functions used by the text area classes
 * Copyright (C) 1999 Slava Pestov
 *
 * You may use and modify this package for any purpose. Redistribution is
 * permitted, in both source and binary form, provided that this notice
 * remains intact in all source distributions of this package.
 */

import javax.swing.text.BadLocationException;
import javax.swing.text.Document;

/**
 * Class with several utility functions used by the text area component.
 * 
 * @author Slava Pestov
 * @version $Id$
 */
public class TextUtilities {
    /**
     * Returns the offset of the bracket matching the one at the specified offset
     * of the document, or -1 if the bracket is unmatched (or if the character is
     * not a bracket).
     * 
     * @param doc
     *           The document
     * @param offset
     *           The offset
     * @exception BadLocationException
     *               If an out-of-bounds access was attempted on the document
     *               text
     */
    public static int findMatchingBracket(Document doc, int offset) throws BadLocationException {
        if (doc.getLength() == 0)
            return -1;
        char c = doc.getText(offset, 1).charAt(0);
        char cprime; // c` - corresponding character
        boolean direction; // true = back, false = forward

        switch (c) {
        case '(':
            cprime = ')';
            direction = false;
            break;
        case ')':
            cprime = '(';
            direction = true;
            break;
        case '[':
            cprime = ']';
            direction = false;
            break;
        case ']':
            cprime = '[';
            direction = true;
            break;
        case '{':
            cprime = '}';
            direction = false;
            break;
        case '}':
            cprime = '{';
            direction = true;
            break;
        default:
            return -1;
        }

        int count;

        // How to merge these two cases is left as an exercise
        // for the reader.

        // Go back or forward
        if (direction) {
            // Count is 1 initially because we have already
            // `found' one closing bracket
            count = 1;

            // Get text[0,offset-1];
            String text = doc.getText(0, offset);

            // Scan backwards
            for (int i = offset - 1; i >= 0; i--) {
                // If text[i] == c, we have found another
                // closing bracket, therefore we will need
                // two opening brackets to complete the
                // match.
                char x = text.charAt(i);
                if (x == c)
                    count++;

                // If text[i] == cprime, we have found a
                // opening bracket, so we return i if
                // --count == 0
                else if (x == cprime) {
                    if (--count == 0)
                        return i;
                }
            }
        } else {
            // Count is 1 initially because we have already
            // `found' one opening bracket
            count = 1;

            // So we don't have to + 1 in every loop
            offset++;

            // Number of characters to check
            int len = doc.getLength() - offset;

            // Get text[offset+1,len];
            String text = doc.getText(offset, len);

            // Scan forwards
            for (int i = 0; i < len; i++) {
                // If text[i] == c, we have found another
                // opening bracket, therefore we will need
                // two closing brackets to complete the
                // match.
                char x = text.charAt(i);

                if (x == c)
                    count++;

                // If text[i] == cprime, we have found an
                // closing bracket, so we return i if
                // --count == 0
                else if (x == cprime) {
                    if (--count == 0)
                        return i + offset;
                }
            }
        }

        // Nothing found
        return -1;
    }

}