CharRepertoire.java

package com.thaiopensource.xml.out;

import java.io.UnsupportedEncodingException;

public class CharRepertoire {
  private final byte[] allUnknown = new byte[256];
  private final byte[][] charTable = new byte[256][];

  private static final byte UNKNOWN = 0;
  private static final byte IN = 1;
  private static final byte OUT = -1;
  
  private final String enc;

  CharRepertoire(String enc) {
    this.enc = enc;
    for (int i = 0; i < charTable.length; i++)
      charTable[i] = allUnknown;
  }

  public static CharRepertoire getInstance(String enc)
    throws UnsupportedEncodingException {
    "x".getBytes(enc);		// check whether encoding supported
    return new CharRepertoire(enc);
  }

  public final boolean contains(char c) {
    byte b = charTable[c >> 8][c & 0xFF];
    return b == 0 ? contains1(c) : b > 0;
  }

  private boolean contains1(char c) {
    int i = c >> 8;
    if (charTable[i] == allUnknown)
      charTable[i] = new byte[256];
    if (contains2(c)) {
      charTable[i][c & 0xFF] = IN;
      return true;
    }
    else {
      charTable[i][c & 0xFF] = OUT;
      return false;
    }
  }

  private boolean contains2(char c) {
    try {
      String s = new String(new String(new char[]{ c }).getBytes(enc), enc);
      return s.length() == 1 && s.charAt(0) == c;
    }
    catch (UnsupportedEncodingException e) {
      return false;
    }
  }

  /* For surrogates. */
  public final boolean contains(char c1, char c2) {
    try {
      String s = new String(new String(new char[]{c1, c2}).getBytes(enc), enc);
      return s.length() == 2 && s.charAt(0) == c1 && s.charAt(1) == c2;
    }
    catch (UnsupportedEncodingException e) {
      return false;
    }
    // work around gcj bug (libgcj/9802)
    catch (RuntimeException e) {
      return false;
    }
  }

}