stringbuilder.java

gcc的组建

/* StringBuilder.java -- Unsynchronized growable strings
   Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
   Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath 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, or (at your option)
any later version.

GNU Classpath 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.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version. */

package java.lang;

import java.io.Serializable;

/**
 * <code>StringBuilder</code> represents a changeable <code>String</code>.
 * It provides the operations required to modify the
 * <code>StringBuilder</code>, including insert, replace, delete, append,
 * and reverse. It like <code>StringBuffer</code>, but is not
 * synchronized.  It is ideal for use when it is known that the
 * object will only be used from a single thread.
 *
 * <p><code>StringBuilder</code>s are variable-length in nature, so even if
 * you initialize them to a certain size, they can still grow larger than
 * that. <em>Capacity</em> indicates the number of characters the
 * <code>StringBuilder</code> can have in it before it has to grow (growing
 * the char array is an expensive operation involving <code>new</code>).
 *
 * <p>Incidentally, compilers often implement the String operator "+"
 * by using a <code>StringBuilder</code> operation:<br>
 * <code>a + b</code><br>
 * is the same as<br>
 * <code>new StringBuilder().append(a).append(b).toString()</code>.
 *
 * <p>Classpath's StringBuilder is capable of sharing memory with Strings for
 * efficiency.  This will help when a StringBuilder is converted to a String
 * and the StringBuilder is not changed after that (quite common when
 * performing string concatenation).
 *
 * @author Paul Fisher
 * @author John Keiser
 * @author Tom Tromey
 * @author Eric Blake ([e-mail])
 * @see String
 * @see StringBuffer
 *
 * @since 1.5
 */
// FIX15: Implement Appendable when co-variant methods are available
public final class StringBuilder
  implements Serializable, CharSequence
{
  // Implementation note: if you change this class, you usually will
  // want to change StringBuffer as well.

  /**
   * For compatability with Sun's JDK
   */
  private static final long serialVersionUID = 4383685877147921099L;

  /**
   * Index of next available character (and thus the size of the current
   * string contents).  Note that this has permissions set this way so that
   * String can get the value.
   *
   * @serial the number of characters in the buffer
   */
  int count;

  /**
   * The buffer.  Note that this has permissions set this way so that String
   * can get the value.
   *
   * @serial the buffer
   */
  char[] value;

  /**
   * The default capacity of a buffer.
   */
  private static final int DEFAULT_CAPACITY = 16;

  /**
   * Create a new StringBuilder with default capacity 16.
   */
  public StringBuilder()
  {
    this(DEFAULT_CAPACITY);
  }

  /**
   * Create an empty <code>StringBuilder</code> with the specified initial
   * capacity.
   *
   * @param capacity the initial capacity
   * @throws NegativeArraySizeException if capacity is negative
   */
  public StringBuilder(int capacity)
  {
    value = new char[capacity];
  }

  /**
   * Create a new <code>StringBuilder</code> with the characters in the
   * specified <code>String</code>. Initial capacity will be the size of the
   * String plus 16.
   *
   * @param str the <code>String</code> to convert
   * @throws NullPointerException if str is null
   */
  public StringBuilder(String str)
  {
    // Unfortunately, because the size is 16 larger, we cannot share.
    count = str.count;
    value = new char[count + DEFAULT_CAPACITY];
    str.getChars(0, count, value, 0);
  }

  /**
   * Create a new <code>StringBuilder</code> with the characters in the
   * specified <code>CharSequence</code>. Initial capacity will be the
   * length of the sequence plus 16; if the sequence reports a length
   * less than or equal to 0, then the initial capacity will be 16.
   *
   * @param seq the initializing <code>CharSequence</code>
   * @throws NullPointerException if str is null
   */
  public StringBuilder(CharSequence seq)
  {
    int len = seq.length();
    count = len <= 0 ? 0 : len;
    value = new char[count + DEFAULT_CAPACITY];
    for (int i = 0; i < len; ++i)
      value[i] = seq.charAt(i);
  }

  /**
   * Get the length of the <code>String</code> this <code>StringBuilder</code>
   * would create. Not to be confused with the <em>capacity</em> of the
   * <code>StringBuilder</code>.
   *
   * @return the length of this <code>StringBuilder</code>
   * @see #capacity()
   * @see #setLength(int)
   */
  public int length()
  {
    return count;
  }

  /**
   * Get the total number of characters this <code>StringBuilder</code> can
   * support before it must be grown.  Not to be confused with <em>length</em>.
   *
   * @return the capacity of this <code>StringBuilder</code>
   * @see #length()
   * @see #ensureCapacity(int)
   */
  public int capacity()
  {
    return value.length;
  }

  /**
   * Increase the capacity of this <code>StringBuilder</code>. This will
   * ensure that an expensive growing operation will not occur until
   * <code>minimumCapacity</code> is reached. The buffer is grown to the
   * larger of <code>minimumCapacity</code> and
   * <code>capacity() * 2 + 2</code>, if it is not already large enough.
   *
   * @param minimumCapacity the new capacity
   * @see #capacity()
   */
  public void ensureCapacity(int minimumCapacity)
  {
    if (minimumCapacity > value.length)
      {
        int max = value.length * 2 + 2;
        minimumCapacity = (minimumCapacity < max ? max : minimumCapacity);
        char[] nb = new char[minimumCapacity];
        System.arraycopy(value, 0, nb, 0, count);
        value = nb;
      }
  }

  /**
   * Set the length of this StringBuilder. If the new length is greater than
   * the current length, all the new characters are set to '\0'. If the new
   * length is less than the current length, the first <code>newLength</code>
   * characters of the old array will be preserved, and the remaining
   * characters are truncated.
   *
   * @param newLength the new length
   * @throws IndexOutOfBoundsException if the new length is negative
   *         (while unspecified, this is a StringIndexOutOfBoundsException)
   * @see #length()
   */
  public void setLength(int newLength)
  {
    if (newLength < 0)
      throw new StringIndexOutOfBoundsException(newLength);

    int valueLength = value.length;

    /* Always call ensureCapacity in order to preserve copy-on-write
       semantics.  */
    ensureCapacity(newLength);

    if (newLength < valueLength)
      {
        /* If the StringBuilder's value just grew, then we know that
           value is newly allocated and the region between count and
           newLength is filled with '\0'.  */
	count = newLength;
      }
    else
      {
	/* The StringBuilder's value doesn't need to grow.  However,
	   we should clear out any cruft that may exist.  */
	while (count < newLength)
          value[count++] = '\0';
      }
  }

  /**
   * Get the character at the specified index.
   *
   * @param index the index of the character to get, starting at 0
   * @return the character at the specified index
   * @throws IndexOutOfBoundsException if index is negative or &gt;= length()
   *         (while unspecified, this is a StringIndexOutOfBoundsException)
   */
  public char charAt(int index)
  {
    if (index < 0 || index >= count)
      throw new StringIndexOutOfBoundsException(index);
    return value[index];
  }

  /**
   * Get the specified array of characters. <code>srcOffset - srcEnd</code>
   * characters will be copied into the array you pass in.
   *
   * @param srcOffset the index to start copying from (inclusive)
   * @param srcEnd the index to stop copying from (exclusive)
   * @param dst the array to copy into
   * @param dstOffset the index to start copying into
   * @throws NullPointerException if dst is null
   * @throws IndexOutOfBoundsException if any source or target indices are
   *         out of range (while unspecified, source problems cause a
   *         StringIndexOutOfBoundsException, and dest problems cause an
   *         ArrayIndexOutOfBoundsException)
   * @see System#arraycopy(Object, int, Object, int, int)
   */
  public void getChars(int srcOffset, int srcEnd,
		       char[] dst, int dstOffset)
  {
    if (srcOffset < 0 || srcEnd > count || srcEnd < srcOffset)
      throw new StringIndexOutOfBoundsException();
    System.arraycopy(value, srcOffset, dst, dstOffset, srcEnd - srcOffset);
  }

  /**
   * Set the character at the specified index.
   *
   * @param index the index of the character to set starting at 0
   * @param ch the value to set that character to
   * @throws IndexOutOfBoundsException if index is negative or &gt;= length()
   *         (while unspecified, this is a StringIndexOutOfBoundsException)
   */
  public void setCharAt(int index, char ch)
  {
    if (index < 0 || index >= count)
      throw new StringIndexOutOfBoundsException(index);
    // Call ensureCapacity to enforce copy-on-write.
    ensureCapacity(count);
    value[index] = ch;
  }

  /**
   * Append the <code>String</code> value of the argument to this
   * <code>StringBuilder</code>. Uses <code>String.valueOf()</code> to convert
   * to <code>String</code>.
   *
   * @param obj the <code>Object</code> to convert and append
   * @return this <code>StringBuilder</code>
   * @see String#valueOf(Object)
   * @see #append(String)
   */
  public StringBuilder append(Object obj)
  {
    return append(obj == null ? "null" : obj.toString());
  }

  /**
   * Append the <code>String</code> to this <code>StringBuilder</code>. If
   * str is null, the String "null" is appended.
   *
   * @param str the <code>String</code> to append
   * @return this <code>StringBuilder</code>
   */
  public StringBuilder append(String str)
  {
    if (str == null)
      str = "null";
    int len = str.count;
    ensureCapacity(count + len);