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Concurrent Radix Trees and Concurrent Suffix Trees for Java.
There is a newer version: 2.6.1
/**
 * Copyright 2012-2013 Niall Gallagher
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.googlecode.concurrenttrees.common;

import java.io.UnsupportedEncodingException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.nio.charset.CharsetEncoder;
import java.nio.charset.CodingErrorAction;
import java.util.Iterator;

/**
 * @author Niall Gallagher
 */
public class CharSequences {

    /**
     * Private constructor, not used.
     */
    CharSequences() {
    }

    public static Iterable generateSuffixes(final CharSequence input) {
        return new Iterable() {
            @Override
            public Iterator iterator() {
                return new Iterator() {
                    int currentIndex = 0;
                    @Override
                    public boolean hasNext() {
                        return currentIndex < input.length();
                    }

                    @Override
                    public CharSequence next() {
                        return input.subSequence(currentIndex++, input.length());
                    }

                    @Override
                    public void remove() {
                        throw new UnsupportedOperationException("Modification not supported");
                    }
                };
            }
        };
    }

    public static Iterable generatePrefixes(final CharSequence input) {
        return new Iterable() {
            @Override
            public Iterator iterator() {
                return new Iterator() {
                    int currentIndex = 0;
                    @Override
                    public boolean hasNext() {
                        return currentIndex < input.length();
                    }

                    @Override
                    public CharSequence next() {
                        return input.subSequence(0, ++currentIndex);
                    }

                    @Override
                    public void remove() {
                        throw new UnsupportedOperationException("Modification not supported");
                    }
                };
            }
        };
    }

    public static CharSequence getCommonPrefix(CharSequence first, CharSequence second) {
        int minLength = Math.min(first.length(), second.length());
        for (int i = 0; i < minLength; i++) {
            if (first.charAt(i) != second.charAt(i)) {
                return first.subSequence(0, i);
            }
        }
        return first.subSequence(0, minLength);
    }

    public static CharSequence getSuffix(CharSequence input, int startIndex) {
        if (startIndex >= input.length()) {
            return "";
        }
        return input.subSequence(startIndex, input.length());
    }

    public static CharSequence getPrefix(CharSequence input, int endIndex) {
        if (endIndex > input.length()) {
            return input;
        }
        return input.subSequence(0, endIndex);
    }

    public static CharSequence subtractPrefix(CharSequence main, CharSequence prefix) {
        int startIndex = prefix.length();
        int mainLength = main.length();
        if (startIndex > mainLength) {
            return "";
        }
        return main.subSequence(startIndex, mainLength);
    }

    public static CharSequence concatenate(final CharSequence first, final CharSequence second) {
        return new StringBuilder().append(first).append(second);
    }

    public static CharSequence reverse(CharSequence input) {
        return new StringBuilder(input.length()).append(input).reverse();
    }

    /**
     * Returns a {@link CharSequence} which wraps the given {@code char[]}. Note that this {@link CharSequence} will
     * reflect any changes to the {@code char[]}.
     *
     * @param characters The {@code char[]} to wrap
     * @return A {@link CharSequence} which wraps the given {@code char[]}
     */
    public static CharSequence fromCharArray(final char[] characters) {
        return new StringBuilder(characters.length).append(characters);
    }

    /**
     * Copies the given {@link CharSequence} into a new {@code char[]}.
     *
     * @param charSequence The {@link CharSequence} to copy
     * @return A new {@code char[]} populated with characters from the given {@link CharSequence}
     */
    public static char[] toCharArray(CharSequence charSequence) {
        final int numChars = charSequence.length();
        char[] charArray = new char[numChars];
        for (int i = 0; i < numChars; i++) {
            charArray[i] = charSequence.charAt(i);
        }
        return charArray;
    }

    public static String toString(CharSequence charSequence) {
        if (charSequence == null) {
            return null;
        }
        if (charSequence instanceof String) {
            return (String)charSequence;
        }
        return new StringBuilder(charSequence.length()).append(charSequence).toString();
    }
}