001    /*
002     * Copyright (C) 2012 eXo Platform SAS.
003     *
004     * This is free software; you can redistribute it and/or modify it
005     * under the terms of the GNU Lesser General Public License as
006     * published by the Free Software Foundation; either version 2.1 of
007     * the License, or (at your option) any later version.
008     *
009     * This software is distributed in the hope that it will be useful,
010     * but WITHOUT ANY WARRANTY; without even the implied warranty of
011     * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
012     * Lesser General Public License for more details.
013     *
014     * You should have received a copy of the GNU Lesser General Public
015     * License along with this software; if not, write to the Free
016     * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
017     * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
018     */
019    
020    package org.crsh.util;
021    
022    /**
023     * An immutable sequence of white spaces.
024     */
025    public class BlankSequence implements CharSequence {
026    
027      /** . */
028      private static final BlankSequence[] CACHE = new BlankSequence[64];
029    
030      static {
031        for (int i = 0;i < CACHE.length;i++) {
032          CACHE[i] = new BlankSequence(i);
033        }
034      }
035    
036      public static BlankSequence create(int length) {
037        if (length < 0) {
038          throw new IllegalArgumentException("No negative length accepted");
039        }
040        if (length < CACHE.length) {
041          return CACHE[length];
042        } else {
043          return new BlankSequence(length);
044        }
045      }
046    
047      /** . */
048      private final int length;
049    
050      /** . */
051      private String value;
052    
053      /**
054       * Build a new blank sequence.
055       *
056       * @param length the length
057       * @throws IllegalArgumentException when length is negative
058       */
059      private BlankSequence(int length) throws IllegalArgumentException {
060        if (length < 0) {
061          throw new IllegalArgumentException();
062        }
063    
064        //
065        this.length = length;
066        this.value = null;
067      }
068    
069      public int length() {
070        return length;
071      }
072    
073      public char charAt(int index) {
074        checkIndex("index", index);
075        return ' ';
076      }
077    
078      public CharSequence subSequence(int start, int end) {
079        checkIndex("start", start);
080        checkIndex("end", end);
081        if (start > end) {
082          throw new IndexOutOfBoundsException("Start " + start + " cannot greater than end " + end);
083        }
084        return new BlankSequence(end - start);
085      }
086    
087      @Override
088      public String toString() {
089        if (value == null) {
090          if (length == 0) {
091            value = "";
092          } else {
093            char[] chars = new char[length];
094            for (int i = 0;i < length;i++) {
095              chars[i] = ' ';
096            }
097            value = new String(chars, 0, chars.length);
098          }
099        }
100        return value;
101      }
102    
103      private void checkIndex(String name, int index) {
104        if (index < 0) {
105          throw new IndexOutOfBoundsException("No negative " + name + " value " + index);
106        }
107        if (index >= length) {
108          throw new IndexOutOfBoundsException("The " + name + " value " + index + " cannot greater than length " + length);
109        }
110      }
111    }