faststringbuffer.java

来自「java jdk 1.4的源码」· Java 代码 · 共 1,377 行 · 第 1/4 页

    m_array = new char[16][0];
    m_array[0] = new char[m_chunkSize];
  }

  /**
   * Directly set how much of the FastStringBuffer's storage is to be
   * considered part of its content. This is a fast but hazardous
   * operation. It is not protected against negative values, or values
   * greater than the amount of storage currently available... and even
   * if additional storage does exist, its contents are unpredictable.
   * The only safe use for our setLength() is to truncate the FastStringBuffer
   * to a shorter string.
   *
   * @param l New length. If l<0 or l>=getLength(), this operation will
   * not report an error but future operations will almost certainly fail.
   */
  public final void setLength(int l)
  {
    m_lastChunk = l >>> m_chunkBits;

    if (m_lastChunk == 0 && m_innerFSB != null)
    {
      // Replace this FSB with the appropriate inner FSB, truncated
      m_innerFSB.setLength(l, this);
    }
    else
    {
      m_firstFree = l & m_chunkMask;
      
	  // There's an edge case if l is an exact multiple of m_chunkBits, which risks leaving
	  // us pointing at the start of a chunk which has not yet been allocated. Rather than 
	  // pay the cost of dealing with that in the append loops (more scattered and more
	  // inner-loop), we correct it here by moving to the safe side of that
	  // line -- as we would have left the indexes had we appended up to that point.
      if(m_firstFree==0 && m_lastChunk>0)
      {
      	--m_lastChunk;
      	m_firstFree=m_chunkSize;
      }
    }
  }

  /**
   * Subroutine for the public setLength() method. Deals with the fact
   * that truncation may require restoring one of the innerFSBs
   *
   * NEEDSDOC @param l
   * NEEDSDOC @param rootFSB
   */
  private final void setLength(int l, FastStringBuffer rootFSB)
  {

    m_lastChunk = l >>> m_chunkBits;

    if (m_lastChunk == 0 && m_innerFSB != null)
    {
      m_innerFSB.setLength(l, rootFSB);
    }
    else
    {

      // Undo encapsulation -- pop the innerFSB data back up to root.
      // Inefficient, but attempts to keep the code simple.
      rootFSB.m_chunkBits = m_chunkBits;
      rootFSB.m_maxChunkBits = m_maxChunkBits;
      rootFSB.m_rebundleBits = m_rebundleBits;
      rootFSB.m_chunkSize = m_chunkSize;
      rootFSB.m_chunkMask = m_chunkMask;
      rootFSB.m_array = m_array;
      rootFSB.m_innerFSB = m_innerFSB;
      rootFSB.m_lastChunk = m_lastChunk;

      // Finally, truncate this sucker.
      rootFSB.m_firstFree = l & m_chunkMask;
    }
  }

  /**
   * Note that this operation has been somewhat deoptimized by the shift to a
   * chunked array, as there is no factory method to produce a String object
   * directly from an array of arrays and hence a double copy is needed.
   * By using ensureCapacity we hope to minimize the heap overhead of building
   * the intermediate StringBuffer.
   * <p>
   * (It really is a pity that Java didn't design String as a final subclass
   * of MutableString, rather than having StringBuffer be a separate hierarchy.
   * We'd avoid a <strong>lot</strong> of double-buffering.)
   *
   * @return the contents of the FastStringBuffer as a standard Java string.
   */
  public final String toString()
  {

    int length = (m_lastChunk << m_chunkBits) + m_firstFree;

    return getString(new StringBuffer(length), 0, 0, length).toString();
  }

  /**
   * Append a single character onto the FastStringBuffer, growing the
   * storage if necessary.
   * <p>
   * NOTE THAT after calling append(), previously obtained
   * references to m_array[][] may no longer be valid....
   * though in fact they should be in this instance.
   *
   * @param value character to be appended.
   */
  public final void append(char value)
  {
    
    char[] chunk;

    // We may have preallocated chunks. If so, all but last should
    // be at full size.
    boolean lastchunk = (m_lastChunk + 1 == m_array.length);

    if (m_firstFree < m_chunkSize)  // Simplified test single-character-fits
      chunk = m_array[m_lastChunk];
    else
    {

      // Extend array?
      int i = m_array.length;

      if (m_lastChunk + 1 == i)
      {
        char[][] newarray = new char[i + 16][];

        System.arraycopy(m_array, 0, newarray, 0, i);

        m_array = newarray;
      }

      // Advance one chunk
      chunk = m_array[++m_lastChunk];

      if (chunk == null)
      {

        // Hierarchical encapsulation
        if (m_lastChunk == 1 << m_rebundleBits
                && m_chunkBits < m_maxChunkBits)
        {

          // Should do all the work of both encapsulating
          // existing data and establishing new sizes/offsets
          m_innerFSB = new FastStringBuffer(this);
        }

        // Add a chunk.
        chunk = m_array[m_lastChunk] = new char[m_chunkSize];
      }

      m_firstFree = 0;
    }

    // Space exists in the chunk. Append the character.
    chunk[m_firstFree++] = value;
  }

  /**
   * Append the contents of a String onto the FastStringBuffer,
   * growing the storage if necessary.
   * <p>
   * NOTE THAT after calling append(), previously obtained
   * references to m_array[] may no longer be valid.
   *
   * @param value String whose contents are to be appended.
   */
  public final void append(String value)
  {

    if (value == null) 
      return;
    int strlen = value.length();

    if (0 == strlen)
      return;

    int copyfrom = 0;
    char[] chunk = m_array[m_lastChunk];
    int available = m_chunkSize - m_firstFree;

    // Repeat while data remains to be copied
    while (strlen > 0)
    {

      // Copy what fits
      if (available > strlen)
        available = strlen;

      value.getChars(copyfrom, copyfrom + available, m_array[m_lastChunk],
                     m_firstFree);

      strlen -= available;
      copyfrom += available;

      // If there's more left, allocate another chunk and continue
      if (strlen > 0)
      {

        // Extend array?
        int i = m_array.length;

        if (m_lastChunk + 1 == i)
        {
          char[][] newarray = new char[i + 16][];

          System.arraycopy(m_array, 0, newarray, 0, i);

          m_array = newarray;
        }

        // Advance one chunk
        chunk = m_array[++m_lastChunk];

        if (chunk == null)
        {

          // Hierarchical encapsulation
          if (m_lastChunk == 1 << m_rebundleBits
                  && m_chunkBits < m_maxChunkBits)
          {

            // Should do all the work of both encapsulating
            // existing data and establishing new sizes/offsets
            m_innerFSB = new FastStringBuffer(this);
          }

          // Add a chunk. 
          chunk = m_array[m_lastChunk] = new char[m_chunkSize];
        }

        available = m_chunkSize;
        m_firstFree = 0;
      }
    }

    // Adjust the insert point in the last chunk, when we've reached it.
    m_firstFree += available;
  }

  /**
   * Append the contents of a StringBuffer onto the FastStringBuffer,
   * growing the storage if necessary.
   * <p>
   * NOTE THAT after calling append(), previously obtained
   * references to m_array[] may no longer be valid.
   *
   * @param value StringBuffer whose contents are to be appended.
   */
  public final void append(StringBuffer value)
  {

    if (value == null) 
      return;
    int strlen = value.length();

    if (0 == strlen)
      return;

    int copyfrom = 0;
    char[] chunk = m_array[m_lastChunk];
    int available = m_chunkSize - m_firstFree;

    // Repeat while data remains to be copied
    while (strlen > 0)
    {

      // Copy what fits
      if (available > strlen)
        available = strlen;

      value.getChars(copyfrom, copyfrom + available, m_array[m_lastChunk],
                     m_firstFree);

      strlen -= available;
      copyfrom += available;

      // If there's more left, allocate another chunk and continue
      if (strlen > 0)
      {

        // Extend array?
        int i = m_array.length;

        if (m_lastChunk + 1 == i)
        {
          char[][] newarray = new char[i + 16][];

          System.arraycopy(m_array, 0, newarray, 0, i);

          m_array = newarray;
        }

        // Advance one chunk
        chunk = m_array[++m_lastChunk];

        if (chunk == null)
        {

          // Hierarchical encapsulation
          if (m_lastChunk == 1 << m_rebundleBits
                  && m_chunkBits < m_maxChunkBits)
          {

            // Should do all the work of both encapsulating
            // existing data and establishing new sizes/offsets
            m_innerFSB = new FastStringBuffer(this);
          }

          // Add a chunk.
          chunk = m_array[m_lastChunk] = new char[m_chunkSize];
        }

        available = m_chunkSize;
        m_firstFree = 0;
      }
    }

    // Adjust the insert point in the last chunk, when we've reached it.
    m_firstFree += available;
  }

  /**
   * Append part of the contents of a Character Array onto the
   * FastStringBuffer,  growing the storage if necessary.
   * <p>
   * NOTE THAT after calling append(), previously obtained
   * references to m_array[] may no longer be valid.
   *
   * @param chars character array from which data is to be copied
   * @param start offset in chars of first character to be copied,
   * zero-based.
   * @param length number of characters to be copied
   */
  public final void append(char[] chars, int start, int length)
  {

    int strlen = length;

    if (0 == strlen)
      return;