Java - Write code to Test to see if the given string equals any of the given terms.

Requirements

Write code to Test to see if the given string equals any of the given terms.

Demo

/*
 * Static String formatting and query routines.
 * Copyright (C) 2001-2005 Stephen Ostermiller
 * http://ostermiller.org/contact.pl?regarding=Java+Utilities
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.//from  w w w.  j  a  v  a 2 s  .  c o  m
 *
 * This program 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 for more details.
 *
 * See COPYING.TXT for details.
 */
 
//package com.book2s;

import java.util.regex.Pattern;

public class Main {
    public static void main(String[] argv) {
        String s = "book2s.com";
        String[] terms = new String[] { "1", "abc", "level", null,
                "book2s.com", "asdf 123" };
        System.out.println(equalsAny(s, terms));
    }

    /**
     * Tests to see if the given string equals any of the given terms.
     * <p>
     * This implementation is more efficient than the brute force approach
     * of testing the string against each of the terms.  It instead compiles
     * a single regular expression that can test all the terms at once, and
     * uses that expression against the string.
     * <p>
     * This is a convenience method.  If multiple strings are tested against
     * the same set of terms, it is more efficient not to compile the regular
     * expression multiple times.
     * @see #getEqualsAnyPattern(String[])
     *
     * @param s String that may equal any of the given terms.
     * @param terms list of strings that may equal the given string.
     * @return true iff one of the terms is equal to the given string.
     *
     * @since ostermillerutils 1.02.25
     */
    public static boolean equalsAny(String s, String[] terms) {
        return getEqualsAnyPattern(terms).matcher(s).matches();
    }

    /**
     * Compile a pattern that can will match a string if the string
     * equals any of the given terms.
     * <p>
     * Usage:<br>
     * <code>boolean b = getEqualsAnyPattern(terms).matcher(s).matches();</code>
     * <p>
     * If multiple strings are matched against the same set of terms,
     * it is more efficient to reuse the pattern returned by this function.
     *
     * @param terms Array of search strings.
     * @return Compiled pattern that can be used to match a string to see if it equals any of the terms.
     *
     * @since ostermillerutils 1.02.25
     */
    public static Pattern getEqualsAnyPattern(String[] terms) {
        StringBuffer sb = new StringBuffer();
        sb.append("(?s)\\A");
        buildFindAnyPattern(terms, sb);
        sb.append("\\z");
        return Pattern.compile(sb.toString());
    }

    /**
     * Build a regular expression that is each of the terms or'd together.
     *
     * @param terms a list of search terms.
     * @param sb place to build the regular expression.
     * @throws IllegalArgumentException if the length of terms is zero.
     *
     * @since ostermillerutils 1.02.25
     */
    private static void buildFindAnyPattern(String[] terms, StringBuffer sb) {
        if (terms.length == 0)
            throw new IllegalArgumentException(
                    "There must be at least one term to find.");
        sb.append("(?:");
        for (int i = 0; i < terms.length; i++) {
            if (i > 0)
                sb.append("|");
            sb.append("(?:");
            sb.append(escapeRegularExpressionLiteral(terms[i]));
            sb.append(")");
        }
        sb.append(")");
    }

    /**
     * Escapes characters that have special meaning to
     * regular expressions
     *
     * @param s String to be escaped
     * @return escaped String
     * @throws NullPointerException if s is null.
     *
     * @since ostermillerutils 1.02.25
     */
    public static String escapeRegularExpressionLiteral(String s) {
        // According to the documentation in the Pattern class:
        //
        // The backslash character ('\') serves to introduce escaped constructs,
        // as defined in the table above, as well as to quote characters that
        // otherwise would be interpreted as unescaped constructs. Thus the
        // expression \\ matches a single backslash and \{ matches a left brace.
        //
        // It is an error to use a backslash prior to any alphabetic character
        // that does not denote an escaped construct; these are reserved for future
        // extensions to the regular-expression language. A backslash may be used
        // prior to a non-alphabetic character regardless of whether that character
        // is part of an unescaped construct.
        //
        // As a result, escape everything except [0-9a-zA-Z]

        int length = s.length();
        int newLength = length;
        // first check for characters that might
        // be dangerous and calculate a length
        // of the string that has escapes.
        for (int i = 0; i < length; i++) {
            char c = s.charAt(i);
            if (!((c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z'))) {
                newLength += 1;
            }
        }
        if (length == newLength) {
            // nothing to escape in the string
            return s;
        }
        StringBuffer sb = new StringBuffer(newLength);
        for (int i = 0; i < length; i++) {
            char c = s.charAt(i);
            if (!((c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z'))) {
                sb.append('\\');
            }
            sb.append(c);
        }
        return sb.toString();
    }
}