Java example source code file (Regexp.java)

This example Java source code file (Regexp.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

regexp, string

The Regexp.java Java example source code

/*
 * Copyright (c) 1995, 2004, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package sun.misc;

/**
 * A class to represent a regular expression.  Only handles '*'s.
 * @author  James Gosling
 */

public class Regexp {
    /** if true then the matching process ignores case. */
    public boolean ignoreCase;

    /*
     * regular expressions are carved into three regions: a constant string
     * prefix, a constant string suffix, and a series of floating strings in
     * between.  In the input regular expression, they are separated by *s
     */
    public String exp;
    public String prefix, suffix;
    public boolean exact;
    public int prefixLen, suffixLen, totalLen;
    public String mids[];

    /** Create a new regular expression object.  The regular expression
        is a series of constant strings separated by *s.  For example:
        <dl>
        <dt>*.gif       
Matches any string that ends in ".gif".
        <dt>/tmp/*      
Matches any string that starts with "/tmp/".
        <dt>/tmp/*.gif  
Matches any string that starts with "/tmp/" and ends
                        with ".gif".
        <dt>/tmp/*new*.gif 
Matches any string that starts with "/tmp/"
                        and ends with ".gif" and has "new" somewhere in between.
        </dl>
     */
    public Regexp (String s) {
        exp = s;
        int firstst = s.indexOf('*');
        int lastst = s.lastIndexOf('*');
        if (firstst < 0) {
            totalLen = s.length();
            exact = true;       // no * s
        } else {
            prefixLen = firstst;
            if (firstst == 0)
                prefix = null;
            else
                prefix = s.substring(0, firstst);
            suffixLen = s.length() - lastst - 1;
            if (suffixLen == 0)
                suffix = null;
            else
                suffix = s.substring(lastst + 1);
            int nmids = 0;
            int pos = firstst;
            while (pos < lastst && pos >= 0) {
                nmids++;
                pos = s.indexOf('*', pos + 1);
            }
            totalLen = prefixLen + suffixLen;
            if (nmids > 0) {
                mids = new String[nmids];
                pos = firstst;
                for (int i = 0; i < nmids; i++) {
                    pos++;
                    int npos = s.indexOf('*', pos);
                    if (pos < npos) {
                        mids[i] = s.substring(pos, npos);
                        totalLen += mids[i].length();
                    }
                    pos = npos;
                }
            }
        }
    }

    /** Returns true iff the String s matches this regular expression. */
    final boolean matches(String s) {
        return matches(s, 0, s.length());
    }

    /** Returns true iff the substring of s from offset for len characters
        matches this regular expression. */
    boolean matches(String s, int offset, int len) {
        if (exact)
            return len == totalLen &&
                exp.regionMatches(ignoreCase, 0, s, offset, len);
        if (len < totalLen)
            return false;
        if (prefixLen > 0 &&
                !prefix.regionMatches(ignoreCase,
                                      0, s, offset, prefixLen)
                ||
                suffixLen > 0 &&
                !suffix.regionMatches(ignoreCase,
                                      0, s, offset + len - suffixLen,
                                      suffixLen))
            return false;
        if (mids == null)
            return true;
        int nmids = mids.length;
        int spos = offset + prefixLen;
        int limit = offset+len-suffixLen;
        for (int i = 0; i<nmids; i++) {
            String ms = mids[i];
            int ml = ms.length();
            while (spos+ml<=limit &&
                   !ms.regionMatches(ignoreCase,
                                     0, s, spos, ml))
                spos++;
            if (spos+ml>limit)
                return false;
            spos+=ml;
        }
        return true;
    }

}