/*

  * Copyright (c) 2003, 2010, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.  Oracle designates this

  * particular file as subject to the "Classpath" exception as provided

  * by Oracle in the LICENSE file that accompanied this code.

  *

  * This code 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

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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  */

 package java.lang;

 import org.apidesign.bck2brwsr.emul.lang.System;

 /**

  * A mutable sequence of characters.

  * <p>

  * Implements a modifiable string. At any point in time it contains some

  * particular sequence of characters, but the length and content of the

  * sequence can be changed through certain method calls.

  *

  * @author      Michael McCloskey

  * @author      Martin Buchholz

  * @author      Ulf Zibis

  * @since       1.5

  */

 abstract class AbstractStringBuilder implements Appendable, CharSequence {

     /**

      * The value is used for character storage.

      */

     char[] value;

     /**

      * The count is the number of characters used.

      */

     int count;

     /**

      * This no-arg constructor is necessary for serialization of subclasses.

      */

     AbstractStringBuilder() {

     }

     /**

      * Creates an AbstractStringBuilder of the specified capacity.

      */

     AbstractStringBuilder(int capacity) {

         value = new char[capacity];

     }

     /**

      * Returns the length (character count).

      *

      * @return  the length of the sequence of characters currently

      *          represented by this object

      */

     public int length() {

         return count;

     }

     /**

      * Returns the current capacity. The capacity is the amount of storage

      * available for newly inserted characters, beyond which an allocation

      * will occur.

      *

      * @return  the current capacity

      */

     public int capacity() {

         return value.length;

     }

     /**

      * Ensures that the capacity is at least equal to the specified minimum.

      * If the current capacity is less than the argument, then a new internal

      * array is allocated with greater capacity. The new capacity is the

      * larger of:

      * <ul>

      * <li>The <code>minimumCapacity</code> argument.

      * <li>Twice the old capacity, plus <code>2</code>.

      * </ul>

      * If the <code>minimumCapacity</code> argument is nonpositive, this

      * method takes no action and simply returns.

      *

      * @param   minimumCapacity   the minimum desired capacity.

      */

     public void ensureCapacity(int minimumCapacity) {

         if (minimumCapacity > 0)

             ensureCapacityInternal(minimumCapacity);

     }

     /**

      * This method has the same contract as ensureCapacity, but is

      * never synchronized.

      */

     private void ensureCapacityInternal(int minimumCapacity) {

         // overflow-conscious code

         if (minimumCapacity - value.length > 0)

             expandCapacity(minimumCapacity);

     }

     /**

      * This implements the expansion semantics of ensureCapacity with no

      * size check or synchronization.

      */

     void expandCapacity(int minimumCapacity) {

         int newCapacity = value.length * 2 + 2;

         if (newCapacity - minimumCapacity < 0)

             newCapacity = minimumCapacity;

         if (newCapacity < 0) {

             if (minimumCapacity < 0) // overflow

                 throw new OutOfMemoryError();

             newCapacity = Integer.MAX_VALUE;

         }

         value = copyOf(value, newCapacity);

     }

     /**

      * Attempts to reduce storage used for the character sequence.

      * If the buffer is larger than necessary to hold its current sequence of

      * characters, then it may be resized to become more space efficient.

      * Calling this method may, but is not required to, affect the value

      * returned by a subsequent call to the {@link #capacity()} method.

      */

     public void trimToSize() {

         if (count < value.length) {

             value = copyOf(value, count);

         }

     }

     /**

      * Sets the length of the character sequence.

      * The sequence is changed to a new character sequence

      * whose length is specified by the argument. For every nonnegative

      * index <i>k</i> less than <code>newLength</code>, the character at

      * index <i>k</i> in the new character sequence is the same as the

      * character at index <i>k</i> in the old sequence if <i>k</i> is less

      * than the length of the old character sequence; otherwise, it is the

      * null character <code>'&#92;u0000'</code>.

      *

      * In other words, if the <code>newLength</code> argument is less than

      * the current length, the length is changed to the specified length.

      * <p>

      * If the <code>newLength</code> argument is greater than or equal

      * to the current length, sufficient null characters

      * (<code>'&#92;u0000'</code>) are appended so that

      * length becomes the <code>newLength</code> argument.

      * <p>

      * The <code>newLength</code> argument must be greater than or equal

      * to <code>0</code>.

      *

      * @param      newLength   the new length

      * @throws     IndexOutOfBoundsException  if the

      *               <code>newLength</code> argument is negative.

      */

     public void setLength(int newLength) {

         if (newLength < 0)

             throw new StringIndexOutOfBoundsException(newLength);

         ensureCapacityInternal(newLength);

         if (count < newLength) {

             for (; count < newLength; count++)

                 value[count] = '\0';

         } else {

             count = newLength;

         }

     }

     /**

      * Returns the <code>char</code> value in this sequence at the specified index.

      * The first <code>char</code> value is at index <code>0</code>, the next at index

      * <code>1</code>, and so on, as in array indexing.

      * <p>

      * The index argument must be greater than or equal to

      * <code>0</code>, and less than the length of this sequence.

      *

      * <p>If the <code>char</code> value specified by the index is a

      * <a href="Character.html#unicode">surrogate</a>, the surrogate

      * value is returned.

      *

      * @param      index   the index of the desired <code>char</code> value.

      * @return     the <code>char</code> value at the specified index.

      * @throws     IndexOutOfBoundsException  if <code>index</code> is

      *             negative or greater than or equal to <code>length()</code>.

      */

     public char charAt(int index) {

         if ((index < 0) || (index >= count))

             throw new StringIndexOutOfBoundsException(index);

         return value[index];

     }

     /**

      * Returns the character (Unicode code point) at the specified

      * index. The index refers to <code>char</code> values

      * (Unicode code units) and ranges from <code>0</code> to

      * {@link #length()}<code> - 1</code>.

      *

      * <p> If the <code>char</code> value specified at the given index

      * is in the high-surrogate range, the following index is less

      * than the length of this sequence, and the

      * <code>char</code> value at the following index is in the

      * low-surrogate range, then the supplementary code point

      * corresponding to this surrogate pair is returned. Otherwise,

      * the <code>char</code> value at the given index is returned.

      *

      * @param      index the index to the <code>char</code> values

      * @return     the code point value of the character at the

      *             <code>index</code>

      * @exception  IndexOutOfBoundsException  if the <code>index</code>

      *             argument is negative or not less than the length of this

      *             sequence.

      */

     public int codePointAt(int index) {

         if ((index < 0) || (index >= count)) {

             throw new StringIndexOutOfBoundsException(index);

         }

         return Character.codePointAt(value, index);

     }

     /**

      * Returns the character (Unicode code point) before the specified

      * index. The index refers to <code>char</code> values

      * (Unicode code units) and ranges from <code>1</code> to {@link

      * #length()}.

      *

      * <p> If the <code>char</code> value at <code>(index - 1)</code>

      * is in the low-surrogate range, <code>(index - 2)</code> is not

      * negative, and the <code>char</code> value at <code>(index -

      * 2)</code> is in the high-surrogate range, then the

      * supplementary code point value of the surrogate pair is

      * returned. If the <code>char</code> value at <code>index -

      * 1</code> is an unpaired low-surrogate or a high-surrogate, the

      * surrogate value is returned.

      *

      * @param     index the index following the code point that should be returned

      * @return    the Unicode code point value before the given index.

      * @exception IndexOutOfBoundsException if the <code>index</code>

      *            argument is less than 1 or greater than the length

      *            of this sequence.

      */

     public int codePointBefore(int index) {

         int i = index - 1;

         if ((i < 0) || (i >= count)) {

             throw new StringIndexOutOfBoundsException(index);

         }

         return Character.codePointBefore(value, index);

     }

     /**

      * Returns the number of Unicode code points in the specified text

      * range of this sequence. The text range begins at the specified

      * <code>beginIndex</code> and extends to the <code>char</code> at

      * index <code>endIndex - 1</code>. Thus the length (in

      * <code>char</code>s) of the text range is

      * <code>endIndex-beginIndex</code>. Unpaired surrogates within

      * this sequence count as one code point each.

      *

      * @param beginIndex the index to the first <code>char</code> of

      * the text range.

      * @param endIndex the index after the last <code>char</code> of

      * the text range.

      * @return the number of Unicode code points in the specified text

      * range

      * @exception IndexOutOfBoundsException if the

      * <code>beginIndex</code> is negative, or <code>endIndex</code>

      * is larger than the length of this sequence, or

      * <code>beginIndex</code> is larger than <code>endIndex</code>.

      */

     public int codePointCount(int beginIndex, int endIndex) {

         if (beginIndex < 0 || endIndex > count || beginIndex > endIndex) {

             throw new IndexOutOfBoundsException();

         }

         return Character.codePointCountImpl(value, beginIndex, endIndex-beginIndex);

     }

     /**

      * Returns the index within this sequence that is offset from the

      * given <code>index</code> by <code>codePointOffset</code> code

      * points. Unpaired surrogates within the text range given by

      * <code>index</code> and <code>codePointOffset</code> count as

      * one code point each.

      *

      * @param index the index to be offset

      * @param codePointOffset the offset in code points

      * @return the index within this sequence

      * @exception IndexOutOfBoundsException if <code>index</code>

      *   is negative or larger then the length of this sequence,

      *   or if <code>codePointOffset</code> is positive and the subsequence

      *   starting with <code>index</code> has fewer than

      *   <code>codePointOffset</code> code points,

      *   or if <code>codePointOffset</code> is negative and the subsequence

      *   before <code>index</code> has fewer than the absolute value of

      *   <code>codePointOffset</code> code points.

      */

     public int offsetByCodePoints(int index, int codePointOffset) {

         if (index < 0 || index > count) {

             throw new IndexOutOfBoundsException();

         }

         return Character.offsetByCodePointsImpl(value, 0, count,

                                                 index, codePointOffset);

     }

     /**

      * Characters are copied from this sequence into the

      * destination character array <code>dst</code>. The first character to

      * be copied is at index <code>srcBegin</code>; the last character to

      * be copied is at index <code>srcEnd-1</code>. The total number of

      * characters to be copied is <code>srcEnd-srcBegin</code>. The

      * characters are copied into the subarray of <code>dst</code> starting

      * at index <code>dstBegin</code> and ending at index:

      * <p><blockquote><pre>

      * dstbegin + (srcEnd-srcBegin) - 1

      * </pre></blockquote>

      *

      * @param      srcBegin   start copying at this offset.

      * @param      srcEnd     stop copying at this offset.

      * @param      dst        the array to copy the data into.

      * @param      dstBegin   offset into <code>dst</code>.

      * @throws     NullPointerException if <code>dst</code> is

      *             <code>null</code>.

      * @throws     IndexOutOfBoundsException  if any of the following is true:

      *             <ul>

      *             <li><code>srcBegin</code> is negative

      *             <li><code>dstBegin</code> is negative

      *             <li>the <code>srcBegin</code> argument is greater than

      *             the <code>srcEnd</code> argument.

      *             <li><code>srcEnd</code> is greater than

      *             <code>this.length()</code>.

      *             <li><code>dstBegin+srcEnd-srcBegin</code> is greater than

      *             <code>dst.length</code>

      *             </ul>

      */

     public void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)

     {

         if (srcBegin < 0)

             throw new StringIndexOutOfBoundsException(srcBegin);

         if ((srcEnd < 0) || (srcEnd > count))

             throw new StringIndexOutOfBoundsException(srcEnd);

         if (srcBegin > srcEnd)

             throw new StringIndexOutOfBoundsException("srcBegin > srcEnd");

         System.arraycopy(value, srcBegin, dst, dstBegin, srcEnd - srcBegin);

     }

     /**

      * The character at the specified index is set to <code>ch</code>. This

      * sequence is altered to represent a new character sequence that is

      * identical to the old character sequence, except that it contains the

      * character <code>ch</code> at position <code>index</code>.

      * <p>

      * The index argument must be greater than or equal to

      * <code>0</code>, and less than the length of this sequence.

      *

      * @param      index   the index of the character to modify.

      * @param      ch      the new character.

      * @throws     IndexOutOfBoundsException  if <code>index</code> is

      *             negative or greater than or equal to <code>length()</code>.

      */

     public void setCharAt(int index, char ch) {

         if ((index < 0) || (index >= count))

             throw new StringIndexOutOfBoundsException(index);

         value[index] = ch;

     }

     /**

      * Appends the string representation of the {@code Object} argument.

      * <p>

      * The overall effect is exactly as if the argument were converted

      * to a string by the method {@link String#valueOf(Object)},

      * and the characters of that string were then

      * {@link #append(String) appended} to this character sequence.

      *

      * @param   obj   an {@code Object}.

      * @return  a reference to this object.

      */

     public AbstractStringBuilder append(Object obj) {

         return append(String.valueOf(obj));

     }

     /**

      * Appends the specified string to this character sequence.

      * <p>

      * The characters of the {@code String} argument are appended, in

      * order, increasing the length of this sequence by the length of the

      * argument. If {@code str} is {@code null}, then the four

      * characters {@code "null"} are appended.

      * <p>

      * Let <i>n</i> be the length of this character sequence just prior to

      * execution of the {@code append} method. Then the character at

      * index <i>k</i> in the new character sequence is equal to the character

      * at index <i>k</i> in the old character sequence, if <i>k</i> is less

      * than <i>n</i>; otherwise, it is equal to the character at index

      * <i>k-n</i> in the argument {@code str}.

      *

      * @param   str   a string.

      * @return  a reference to this object.

      */

     public AbstractStringBuilder append(String str) {

         if (str == null) str = "null";

         int len = str.length();

         ensureCapacityInternal(count + len);

         str.getChars(0, len, value, count);

         count += len;

         return this;

     }

     // Documentation in subclasses because of synchro difference

     public AbstractStringBuilder append(StringBuffer sb) {

         if (sb == null)

             return append("null");

         int len = sb.length();

         ensureCapacityInternal(count + len);

         sb.getChars(0, len, value, count);

         count += len;

         return this;

     }

     // Documentation in subclasses because of synchro difference

     public AbstractStringBuilder append(CharSequence s) {

         if (s == null)

             s = "null";

         if (s instanceof String)

             return this.append((String)s);

         if (s instanceof StringBuffer)

             return this.append((StringBuffer)s);

         return this.append(s, 0, s.length());

     }

     /**

      * Appends a subsequence of the specified {@code CharSequence} to this

      * sequence.

      * <p>

      * Characters of the argument {@code s}, starting at

      * index {@code start}, are appended, in order, to the contents of

      * this sequence up to the (exclusive) index {@code end}. The length

      * of this sequence is increased by the value of {@code end - start}.

      * <p>

      * Let <i>n</i> be the length of this character sequence just prior to

      * execution of the {@code append} method. Then the character at

      * index <i>k</i> in this character sequence becomes equal to the

      * character at index <i>k</i> in this sequence, if <i>k</i> is less than

      * <i>n</i>; otherwise, it is equal to the character at index

      * <i>k+start-n</i> in the argument {@code s}.

      * <p>

      * If {@code s} is {@code null}, then this method appends

      * characters as if the s parameter was a sequence containing the four

      * characters {@code "null"}.

      *

      * @param   s the sequence to append.

      * @param   start   the starting index of the subsequence to be appended.

      * @param   end     the end index of the subsequence to be appended.

      * @return  a reference to this object.

      * @throws     IndexOutOfBoundsException if

      *             {@code start} is negative, or

      *             {@code start} is greater than {@code end} or

      *             {@code end} is greater than {@code s.length()}

      */

     public AbstractStringBuilder append(CharSequence s, int start, int end) {

         if (s == null)

             s = "null";

         if ((start < 0) || (start > end) || (end > s.length()))

             throw new IndexOutOfBoundsException(

                 "start " + start + ", end " + end + ", s.length() "

                 + s.length());

         int len = end - start;

         ensureCapacityInternal(count + len);

         for (int i = start, j = count; i < end; i++, j++)

             value[j] = s.charAt(i);

         count += len;

         return this;

     }

     /**

      * Appends the string representation of the {@code char} array

      * argument to this sequence.

      * <p>

      * The characters of the array argument are appended, in order, to

      * the contents of this sequence. The length of this sequence

      * increases by the length of the argument.

      * <p>

      * The overall effect is exactly as if the argument were converted

      * to a string by the method {@link String#valueOf(char[])},

      * and the characters of that string were then

      * {@link #append(String) appended} to this character sequence.

      *

      * @param   str   the characters to be appended.

      * @return  a reference to this object.

      */

     public AbstractStringBuilder append(char[] str) {

         int len = str.length;

         ensureCapacityInternal(count + len);

         System.arraycopy(str, 0, value, count, len);

         count += len;

         return this;

     }

     /**

      * Appends the string representation of a subarray of the

      * {@code char} array argument to this sequence.

      * <p>

      * Characters of the {@code char} array {@code str}, starting at

      * index {@code offset}, are appended, in order, to the contents

      * of this sequence. The length of this sequence increases

      * by the value of {@code len}.

      * <p>

      * The overall effect is exactly as if the arguments were converted

      * to a string by the method {@link String#valueOf(char[],int,int)},

      * and the characters of that string were then

      * {@link #append(String) appended} to this character sequence.

      *

      * @param   str      the characters to be appended.

      * @param   offset   the index of the first {@code char} to append.

      * @param   len      the number of {@code char}s to append.

      * @return  a reference to this object.

      * @throws IndexOutOfBoundsException

      *         if {@code offset < 0} or {@code len < 0}

      *         or {@code offset+len > str.length}

      */

     public AbstractStringBuilder append(char str[], int offset, int len) {

         if (len > 0)                // let arraycopy report AIOOBE for len < 0

             ensureCapacityInternal(count + len);

         System.arraycopy(str, offset, value, count, len);

         count += len;

         return this;

     }

     /**

      * Appends the string representation of the {@code boolean}

      * argument to the sequence.

      * <p>

      * The overall effect is exactly as if the argument were converted

      * to a string by the method {@link String#valueOf(boolean)},

      * and the characters of that string were then

      * {@link #append(String) appended} to this character sequence.

      *

      * @param   b   a {@code boolean}.

      * @return  a reference to this object.

      */

     public AbstractStringBuilder append(boolean b) {

         if (b) {

             ensureCapacityInternal(count + 4);

             value[count++] = 't';

             value[count++] = 'r';

             value[count++] = 'u';

             value[count++] = 'e';

         } else {

             ensureCapacityInternal(count + 5);

             value[count++] = 'f';

             value[count++] = 'a';

             value[count++] = 'l';

             value[count++] = 's';

             value[count++] = 'e';

         }

         return this;

     }

     /**

      * Appends the string representation of the {@code char}

      * argument to this sequence.

      * <p>

      * The argument is appended to the contents of this sequence.

      * The length of this sequence increases by {@code 1}.

      * <p>

      * The overall effect is exactly as if the argument were converted

      * to a string by the method {@link String#valueOf(char)},

      * and the character in that string were then

      * {@link #append(String) appended} to this character sequence.

      *

      * @param   c   a {@code char}.

      * @return  a reference to this object.

      */

     public AbstractStringBuilder append(char c) {

         ensureCapacityInternal(count + 1);

         value[count++] = c;

         return this;

     }

     /**

      * Appends the string representation of the {@code int}

      * argument to this sequence.

      * <p>

      * The overall effect is exactly as if the argument were converted

      * to a string by the method {@link String#valueOf(int)},

      * and the characters of that string were then

      * {@link #append(String) appended} to this character sequence.

      *

      * @param   i   an {@code int}.

      * @return  a reference to this object.

      */

     public AbstractStringBuilder append(int i) {

         return append(Integer.toString(i));

     }

     /**

      * Appends the string representation of the {@code long}

      * argument to this sequence.

      * <p>

      * The overall effect is exactly as if the argument were converted

      * to a string by the method {@link String#valueOf(long)},

      * and the characters of that string were then

      * {@link #append(String) appended} to this character sequence.

      *

      * @param   l   a {@code long}.

      * @return  a reference to this object.

      */

     public AbstractStringBuilder append(long l) {

         if (l == Long.MIN_VALUE) {

             append("-9223372036854775808");

             return this;

         }

         int appendedLength = (l < 0) ? Long.stringSize(-l) + 1

                                      : Long.stringSize(l);

         int spaceNeeded = count + appendedLength;

         ensureCapacityInternal(spaceNeeded);

         Long.getChars(l, spaceNeeded, value);

         count = spaceNeeded;

         return this;

     }

     /**

      * Appends the string representation of the {@code float}

      * argument to this sequence.

      * <p>

      * The overall effect is exactly as if the argument were converted

      * to a string by the method {@link String#valueOf(float)},

      * and the characters of that string were then

      * {@link #append(String) appended} to this character sequence.

      *

      * @param   f   a {@code float}.

      * @return  a reference to this object.

      */

     public AbstractStringBuilder append(float f) {

         return append(Float.toString(f));

     }

     /**

      * Appends the string representation of the {@code double}

      * argument to this sequence.

      * <p>

      * The overall effect is exactly as if the argument were converted

      * to a string by the method {@link String#valueOf(double)},

      * and the characters of that string were then

      * {@link #append(String) appended} to this character sequence.

      *

      * @param   d   a {@code double}.

      * @return  a reference to this object.

      */

     public AbstractStringBuilder append(double d) {

         return append(Double.toString(d));

     }

     /**

      * Removes the characters in a substring of this sequence.

      * The substring begins at the specified {@code start} and extends to

      * the character at index {@code end - 1} or to the end of the

      * sequence if no such character exists. If

      * {@code start} is equal to {@code end}, no changes are made.

      *

      * @param      start  The beginning index, inclusive.

      * @param      end    The ending index, exclusive.

      * @return     This object.

      * @throws     StringIndexOutOfBoundsException  if {@code start}

      *             is negative, greater than {@code length()}, or

      *             greater than {@code end}.

      */

     public AbstractStringBuilder delete(int start, int end) {

         if (start < 0)

             throw new StringIndexOutOfBoundsException(start);

         if (end > count)

             end = count;

         if (start > end)

             throw new StringIndexOutOfBoundsException();

         int len = end - start;

         if (len > 0) {

             System.arraycopy(value, start+len, value, start, count-end);

             count -= len;

         }

         return this;

     }

     /**

      * Appends the string representation of the {@code codePoint}

      * argument to this sequence.

      *

      * <p> The argument is appended to the contents of this sequence.

      * The length of this sequence increases by

      * {@link Character#charCount(int) Character.charCount(codePoint)}.

      *

      * <p> The overall effect is exactly as if the argument were

      * converted to a {@code char} array by the method

      * {@link Character#toChars(int)} and the character in that array

      * were then {@link #append(char[]) appended} to this character

      * sequence.

      *

      * @param   codePoint   a Unicode code point

      * @return  a reference to this object.

      * @exception IllegalArgumentException if the specified

      * {@code codePoint} isn't a valid Unicode code point

      */

     public AbstractStringBuilder appendCodePoint(int codePoint) {

         final int count = this.count;

         if (Character.isBmpCodePoint(codePoint)) {

             ensureCapacityInternal(count + 1);

             value[count] = (char) codePoint;

             this.count = count + 1;

         } else if (Character.isValidCodePoint(codePoint)) {

             ensureCapacityInternal(count + 2);

             Character.toSurrogates(codePoint, value, count);

             this.count = count + 2;

         } else {

             throw new IllegalArgumentException();

         }

         return this;

     }

     /**

      * Removes the <code>char</code> at the specified position in this

      * sequence. This sequence is shortened by one <code>char</code>.

      *

      * <p>Note: If the character at the given index is a supplementary

      * character, this method does not remove the entire character. If

      * correct handling of supplementary characters is required,

      * determine the number of <code>char</code>s to remove by calling

      * <code>Character.charCount(thisSequence.codePointAt(index))</code>,

      * where <code>thisSequence</code> is this sequence.

      *

      * @param       index  Index of <code>char</code> to remove

      * @return      This object.

      * @throws      StringIndexOutOfBoundsException  if the <code>index</code>

      *              is negative or greater than or equal to

      *              <code>length()</code>.

      */

     public AbstractStringBuilder deleteCharAt(int index) {

         if ((index < 0) || (index >= count))

             throw new StringIndexOutOfBoundsException(index);

         System.arraycopy(value, index+1, value, index, count-index-1);

         count--;

         return this;

     }

     /**

      * Replaces the characters in a substring of this sequence

      * with characters in the specified <code>String</code>. The substring

      * begins at the specified <code>start</code> and extends to the character

      * at index <code>end - 1</code> or to the end of the

      * sequence if no such character exists. First the

      * characters in the substring are removed and then the specified

      * <code>String</code> is inserted at <code>start</code>. (This

      * sequence will be lengthened to accommodate the

      * specified String if necessary.)

      *

      * @param      start    The beginning index, inclusive.

      * @param      end      The ending index, exclusive.

      * @param      str   String that will replace previous contents.

      * @return     This object.

      * @throws     StringIndexOutOfBoundsException  if <code>start</code>

      *             is negative, greater than <code>length()</code>, or

      *             greater than <code>end</code>.

      */

     public AbstractStringBuilder replace(int start, int end, String str) {

         if (start < 0)

             throw new StringIndexOutOfBoundsException(start);

         if (start > count)

             throw new StringIndexOutOfBoundsException("start > length()");

         if (start > end)

             throw new StringIndexOutOfBoundsException("start > end");

         if (end > count)

             end = count;

         int len = str.length();

         int newCount = count + len - (end - start);

         ensureCapacityInternal(newCount);

         System.arraycopy(value, end, value, start + len, count - end);

         str.getChars(value, start);

         count = newCount;

         return this;

     }

     /**

      * Returns a new <code>String</code> that contains a subsequence of

      * characters currently contained in this character sequence. The

      * substring begins at the specified index and extends to the end of

      * this sequence.

      *

      * @param      start    The beginning index, inclusive.

      * @return     The new string.

      * @throws     StringIndexOutOfBoundsException  if <code>start</code> is

      *             less than zero, or greater than the length of this object.

      */

     public String substring(int start) {

         return substring(start, count);

     }

     /**

      * Returns a new character sequence that is a subsequence of this sequence.

      *

      * <p> An invocation of this method of the form

      *

      * <blockquote><pre>

      * sb.subSequence(begin,&nbsp;end)</pre></blockquote>

      *

      * behaves in exactly the same way as the invocation

      *

      * <blockquote><pre>

      * sb.substring(begin,&nbsp;end)</pre></blockquote>

      *

      * This method is provided so that this class can

      * implement the {@link CharSequence} interface. </p>

      *

      * @param      start   the start index, inclusive.

      * @param      end     the end index, exclusive.

      * @return     the specified subsequence.

      *

      * @throws  IndexOutOfBoundsException

      *          if <tt>start</tt> or <tt>end</tt> are negative,

      *          if <tt>end</tt> is greater than <tt>length()</tt>,

      *          or if <tt>start</tt> is greater than <tt>end</tt>

      * @spec JSR-51

      */

     public CharSequence subSequence(int start, int end) {

         return substring(start, end);

     }

     /**

      * Returns a new <code>String</code> that contains a subsequence of

      * characters currently contained in this sequence. The

      * substring begins at the specified <code>start</code> and

      * extends to the character at index <code>end - 1</code>.

      *

      * @param      start    The beginning index, inclusive.

      * @param      end      The ending index, exclusive.

      * @return     The new string.

      * @throws     StringIndexOutOfBoundsException  if <code>start</code>

      *             or <code>end</code> are negative or greater than

      *             <code>length()</code>, or <code>start</code> is

      *             greater than <code>end</code>.

      */

     public String substring(int start, int end) {

         if (start < 0)

             throw new StringIndexOutOfBoundsException(start);

         if (end > count)

             throw new StringIndexOutOfBoundsException(end);

         if (start > end)

             throw new StringIndexOutOfBoundsException(end - start);

         return new String(value, start, end - start);

     }

     /**

      * Inserts the string representation of a subarray of the {@code str}

      * array argument into this sequence. The subarray begins at the

      * specified {@code offset} and extends {@code len} {@code char}s.

      * The characters of the subarray are inserted into this sequence at

      * the position indicated by {@code index}. The length of this

      * sequence increases by {@code len} {@code char}s.

      *

      * @param      index    position at which to insert subarray.

      * @param      str       A {@code char} array.

      * @param      offset   the index of the first {@code char} in subarray to

      *             be inserted.

      * @param      len      the number of {@code char}s in the subarray to

      *             be inserted.

      * @return     This object

      * @throws     StringIndexOutOfBoundsException  if {@code index}

      *             is negative or greater than {@code length()}, or

      *             {@code offset} or {@code len} are negative, or

      *             {@code (offset+len)} is greater than

      *             {@code str.length}.

      */

     public AbstractStringBuilder insert(int index, char[] str, int offset,

                                         int len)

     {

         if ((index < 0) || (index > length()))

             throw new StringIndexOutOfBoundsException(index);

         if ((offset < 0) || (len < 0) || (offset > str.length - len))

             throw new StringIndexOutOfBoundsException(

                 "offset " + offset + ", len " + len + ", str.length "

                 + str.length);

         ensureCapacityInternal(count + len);

         System.arraycopy(value, index, value, index + len, count - index);

         System.arraycopy(str, offset, value, index, len);

         count += len;

         return this;

     }

     /**

      * Inserts the string representation of the {@code Object}

      * argument into this character sequence.

      * <p>

      * The overall effect is exactly as if the second argument were

      * converted to a string by the method {@link String#valueOf(Object)},

      * and the characters of that string were then

      * {@link #insert(int,String) inserted} into this character

      * sequence at the indicated offset.

      * <p>

      * The {@code offset} argument must be greater than or equal to

      * {@code 0}, and less than or equal to the {@linkplain #length() length}

      * of this sequence.

      *

      * @param      offset   the offset.

      * @param      obj      an {@code Object}.

      * @return     a reference to this object.

      * @throws     StringIndexOutOfBoundsException  if the offset is invalid.

      */

     public AbstractStringBuilder insert(int offset, Object obj) {

         return insert(offset, String.valueOf(obj));

     }

     /**

      * Inserts the string into this character sequence.

      * <p>

      * The characters of the {@code String} argument are inserted, in

      * order, into this sequence at the indicated offset, moving up any

      * characters originally above that position and increasing the length

      * of this sequence by the length of the argument. If

      * {@code str} is {@code null}, then the four characters

      * {@code "null"} are inserted into this sequence.

      * <p>

      * The character at index <i>k</i> in the new character sequence is

      * equal to:

      * <ul>

      * <li>the character at index <i>k</i> in the old character sequence, if

      * <i>k</i> is less than {@code offset}

      * <li>the character at index <i>k</i>{@code -offset} in the

      * argument {@code str}, if <i>k</i> is not less than

      * {@code offset} but is less than {@code offset+str.length()}

      * <li>the character at index <i>k</i>{@code -str.length()} in the

      * old character sequence, if <i>k</i> is not less than

      * {@code offset+str.length()}

      * </ul><p>

      * The {@code offset} argument must be greater than or equal to

      * {@code 0}, and less than or equal to the {@linkplain #length() length}

      * of this sequence.

      *

      * @param      offset   the offset.

      * @param      str      a string.

      * @return     a reference to this object.

      * @throws     StringIndexOutOfBoundsException  if the offset is invalid.

      */

     public AbstractStringBuilder insert(int offset, String str) {

         if ((offset < 0) || (offset > length()))

             throw new StringIndexOutOfBoundsException(offset);

         if (str == null)

             str = "null";

         int len = str.length();

         ensureCapacityInternal(count + len);

         System.arraycopy(value, offset, value, offset + len, count - offset);

         str.getChars(value, offset);

         count += len;

         return this;

     }

     /**

      * Inserts the string representation of the {@code char} array

      * argument into this sequence.

      * <p>

      * The characters of the array argument are inserted into the

      * contents of this sequence at the position indicated by

      * {@code offset}. The length of this sequence increases by

      * the length of the argument.

      * <p>

      * The overall effect is exactly as if the second argument were

      * converted to a string by the method {@link String#valueOf(char[])},

      * and the characters of that string were then

      * {@link #insert(int,String) inserted} into this character

      * sequence at the indicated offset.

      * <p>

      * The {@code offset} argument must be greater than or equal to

      * {@code 0}, and less than or equal to the {@linkplain #length() length}

      * of this sequence.

      *

      * @param      offset   the offset.

      * @param      str      a character array.

      * @return     a reference to this object.

      * @throws     StringIndexOutOfBoundsException  if the offset is invalid.

      */

     public AbstractStringBuilder insert(int offset, char[] str) {

         if ((offset < 0) || (offset > length()))

             throw new StringIndexOutOfBoundsException(offset);

         int len = str.length;

         ensureCapacityInternal(count + len);

         System.arraycopy(value, offset, value, offset + len, count - offset);

         System.arraycopy(str, 0, value, offset, len);

         count += len;

         return this;

     }

     /**

      * Inserts the specified {@code CharSequence} into this sequence.

      * <p>

      * The characters of the {@code CharSequence} argument are inserted,

      * in order, into this sequence at the indicated offset, moving up

      * any characters originally above that position and increasing the length

      * of this sequence by the length of the argument s.

      * <p>

      * The result of this method is exactly the same as if it were an

      * invocation of this object's

      * {@link #insert(int,CharSequence,int,int) insert}(dstOffset, s, 0, s.length())

      * method.

      *

      * <p>If {@code s} is {@code null}, then the four characters

      * {@code "null"} are inserted into this sequence.

      *

      * @param      dstOffset   the offset.

      * @param      s the sequence to be inserted

      * @return     a reference to this object.

      * @throws     IndexOutOfBoundsException  if the offset is invalid.

      */

     public AbstractStringBuilder insert(int dstOffset, CharSequence s) {

         if (s == null)

             s = "null";

         if (s instanceof String)

             return this.insert(dstOffset, (String)s);

         return this.insert(dstOffset, s, 0, s.length());

     }

     /**

      * Inserts a subsequence of the specified {@code CharSequence} into

      * this sequence.

      * <p>

      * The subsequence of the argument {@code s} specified by

      * {@code start} and {@code end} are inserted,

      * in order, into this sequence at the specified destination offset, moving

      * up any characters originally above that position. The length of this

      * sequence is increased by {@code end - start}.

      * <p>

      * The character at index <i>k</i> in this sequence becomes equal to:

      * <ul>

      * <li>the character at index <i>k</i> in this sequence, if

      * <i>k</i> is less than {@code dstOffset}

      * <li>the character at index <i>k</i>{@code +start-dstOffset} in

      * the argument {@code s}, if <i>k</i> is greater than or equal to

      * {@code dstOffset} but is less than {@code dstOffset+end-start}

      * <li>the character at index <i>k</i>{@code -(end-start)} in this

      * sequence, if <i>k</i> is greater than or equal to

      * {@code dstOffset+end-start}

      * </ul><p>

      * The {@code dstOffset} argument must be greater than or equal to

      * {@code 0}, and less than or equal to the {@linkplain #length() length}

      * of this sequence.

      * <p>The start argument must be nonnegative, and not greater than

      * {@code end}.

      * <p>The end argument must be greater than or equal to

      * {@code start}, and less than or equal to the length of s.

      *

      * <p>If {@code s} is {@code null}, then this method inserts

      * characters as if the s parameter was a sequence containing the four

      * characters {@code "null"}.

      *

      * @param      dstOffset   the offset in this sequence.

      * @param      s       the sequence to be inserted.

      * @param      start   the starting index of the subsequence to be inserted.

      * @param      end     the end index of the subsequence to be inserted.

      * @return     a reference to this object.

      * @throws     IndexOutOfBoundsException  if {@code dstOffset}

      *             is negative or greater than {@code this.length()}, or

      *              {@code start} or {@code end} are negative, or

      *              {@code start} is greater than {@code end} or

      *              {@code end} is greater than {@code s.length()}

      */

      public AbstractStringBuilder insert(int dstOffset, CharSequence s,

                                          int start, int end) {

         if (s == null)

             s = "null";

         if ((dstOffset < 0) || (dstOffset > this.length()))

             throw new IndexOutOfBoundsException("dstOffset "+dstOffset);

         if ((start < 0) || (end < 0) || (start > end) || (end > s.length()))

             throw new IndexOutOfBoundsException(

                 "start " + start + ", end " + end + ", s.length() "

                 + s.length());

         int len = end - start;

         ensureCapacityInternal(count + len);

         System.arraycopy(value, dstOffset, value, dstOffset + len,

                          count - dstOffset);

         for (int i=start; i<end; i++)

             value[dstOffset++] = s.charAt(i);

         count += len;

         return this;

     }

     /**

      * Inserts the string representation of the {@code boolean}

      * argument into this sequence.

      * <p>

      * The overall effect is exactly as if the second argument were

      * converted to a string by the method {@link String#valueOf(boolean)},

      * and the characters of that string were then

      * {@link #insert(int,String) inserted} into this character

      * sequence at the indicated offset.

      * <p>

      * The {@code offset} argument must be greater than or equal to

      * {@code 0}, and less than or equal to the {@linkplain #length() length}

      * of this sequence.

      *

      * @param      offset   the offset.

      * @param      b        a {@code boolean}.

      * @return     a reference to this object.

      * @throws     StringIndexOutOfBoundsException  if the offset is invalid.

      */

     public AbstractStringBuilder insert(int offset, boolean b) {

         return insert(offset, String.valueOf(b));

     }

     /**

      * Inserts the string representation of the {@code char}

      * argument into this sequence.

      * <p>

      * The overall effect is exactly as if the second argument were

      * converted to a string by the method {@link String#valueOf(char)},

      * and the character in that string were then

      * {@link #insert(int,String) inserted} into this character

      * sequence at the indicated offset.

      * <p>

      * The {@code offset} argument must be greater than or equal to

      * {@code 0}, and less than or equal to the {@linkplain #length() length}

      * of this sequence.

      *

      * @param      offset   the offset.

      * @param      c        a {@code char}.

      * @return     a reference to this object.

      * @throws     IndexOutOfBoundsException  if the offset is invalid.

      */

     public AbstractStringBuilder insert(int offset, char c) {

         ensureCapacityInternal(count + 1);

         System.arraycopy(value, offset, value, offset + 1, count - offset);

         value[offset] = c;

         count += 1;

         return this;

     }

     /**

      * Inserts the string representation of the second {@code int}

      * argument into this sequence.

      * <p>

      * The overall effect is exactly as if the second argument were

      * converted to a string by the method {@link String#valueOf(int)},

      * and the characters of that string were then

      * {@link #insert(int,String) inserted} into this character

      * sequence at the indicated offset.

      * <p>

      * The {@code offset} argument must be greater than or equal to

      * {@code 0}, and less than or equal to the {@linkplain #length() length}

      * of this sequence.

      *

      * @param      offset   the offset.

      * @param      i        an {@code int}.

      * @return     a reference to this object.

      * @throws     StringIndexOutOfBoundsException  if the offset is invalid.

      */

     public AbstractStringBuilder insert(int offset, int i) {

         return insert(offset, String.valueOf(i));

     }

     /**

      * Inserts the string representation of the {@code long}

      * argument into this sequence.

      * <p>

      * The overall effect is exactly as if the second argument were

      * converted to a string by the method {@link String#valueOf(long)},

      * and the characters of that string were then

      * {@link #insert(int,String) inserted} into this character

      * sequence at the indicated offset.

      * <p>

      * The {@code offset} argument must be greater than or equal to

      * {@code 0}, and less than or equal to the {@linkplain #length() length}

      * of this sequence.

      *

      * @param      offset   the offset.

      * @param      l        a {@code long}.

      * @return     a reference to this object.

      * @throws     StringIndexOutOfBoundsException  if the offset is invalid.

      */

     public AbstractStringBuilder insert(int offset, long l) {

         return insert(offset, String.valueOf(l));

     }

     /**

      * Inserts the string representation of the {@code float}

      * argument into this sequence.

      * <p>

      * The overall effect is exactly as if the second argument were

      * converted to a string by the method {@link String#valueOf(float)},

      * and the characters of that string were then

      * {@link #insert(int,String) inserted} into this character

      * sequence at the indicated offset.

      * <p>

      * The {@code offset} argument must be greater than or equal to

      * {@code 0}, and less than or equal to the {@linkplain #length() length}

      * of this sequence.

      *

      * @param      offset   the offset.

      * @param      f        a {@code float}.

      * @return     a reference to this object.

      * @throws     StringIndexOutOfBoundsException  if the offset is invalid.

      */

     public AbstractStringBuilder insert(int offset, float f) {

         return insert(offset, String.valueOf(f));

     }

     /**

      * Inserts the string representation of the {@code double}

      * argument into this sequence.

      * <p>

      * The overall effect is exactly as if the second argument were

      * converted to a string by the method {@link String#valueOf(double)},

      * and the characters of that string were then

      * {@link #insert(int,String) inserted} into this character

      * sequence at the indicated offset.

      * <p>

      * The {@code offset} argument must be greater than or equal to

      * {@code 0}, and less than or equal to the {@linkplain #length() length}

      * of this sequence.

      *

      * @param      offset   the offset.

      * @param      d        a {@code double}.

      * @return     a reference to this object.

      * @throws     StringIndexOutOfBoundsException  if the offset is invalid.

      */

     public AbstractStringBuilder insert(int offset, double d) {

         return insert(offset, String.valueOf(d));

     }

     /**

      * Returns the index within this string of the first occurrence of the

      * specified substring. The integer returned is the smallest value

      * <i>k</i> such that:

      * <blockquote><pre>

      * this.toString().startsWith(str, <i>k</i>)

      * </pre></blockquote>

      * is <code>true</code>.

      *

      * @param   str   any string.

      * @return  if the string argument occurs as a substring within this

      *          object, then the index of the first character of the first

      *          such substring is returned; if it does not occur as a

      *          substring, <code>-1</code> is returned.

      * @throws  java.lang.NullPointerException if <code>str</code> is

      *          <code>null</code>.

      */

     public int indexOf(String str) {

         return indexOf(str, 0);

     }

     /**

      * Returns the index within this string of the first occurrence of the

      * specified substring, starting at the specified index.  The integer

      * returned is the smallest value <tt>k</tt> for which:

      * <blockquote><pre>

      *     k >= Math.min(fromIndex, str.length()) &&

      *                   this.toString().startsWith(str, k)

      * </pre></blockquote>

      * If no such value of <i>k</i> exists, then -1 is returned.

      *

      * @param   str         the substring for which to search.

      * @param   fromIndex   the index from which to start the search.

      * @return  the index within this string of the first occurrence of the

      *          specified substring, starting at the specified index.

      * @throws  java.lang.NullPointerException if <code>str</code> is

      *            <code>null</code>.

      */

     public int indexOf(String str, int fromIndex) {

         return toString().indexOf(str, fromIndex);

     }

     /**

      * Returns the index within this string of the rightmost occurrence

      * of the specified substring.  The rightmost empty string "" is

      * considered to occur at the index value <code>this.length()</code>.

      * The returned index is the largest value <i>k</i> such that

      * <blockquote><pre>

      * this.toString().startsWith(str, k)

      * </pre></blockquote>

      * is true.

      *

      * @param   str   the substring to search for.

      * @return  if the string argument occurs one or more times as a substring

      *          within this object, then the index of the first character of

      *          the last such substring is returned. If it does not occur as

      *          a substring, <code>-1</code> is returned.

      * @throws  java.lang.NullPointerException  if <code>str</code> is

      *          <code>null</code>.

      */

     public int lastIndexOf(String str) {

         return lastIndexOf(str, count);

     }

     /**

      * Returns the index within this string of the last occurrence of the

      * specified substring. The integer returned is the largest value <i>k</i>

      * such that:

      * <blockquote><pre>

      *     k <= Math.min(fromIndex, str.length()) &&

      *                   this.toString().startsWith(str, k)

      * </pre></blockquote>

      * If no such value of <i>k</i> exists, then -1 is returned.

      *

      * @param   str         the substring to search for.

      * @param   fromIndex   the index to start the search from.

      * @return  the index within this sequence of the last occurrence of the

      *          specified substring.

      * @throws  java.lang.NullPointerException if <code>str</code> is

      *          <code>null</code>.

      */

     public int lastIndexOf(String str, int fromIndex) {

         return String.lastIndexOf(value, 0, count,

                               str.toCharArray(), 0, str.length(), fromIndex);

     }

     /**

      * Causes this character sequence to be replaced by the reverse of

      * the sequence. If there are any surrogate pairs included in the

      * sequence, these are treated as single characters for the

      * reverse operation. Thus, the order of the high-low surrogates

      * is never reversed.

      *

      * Let <i>n</i> be the character length of this character sequence

      * (not the length in <code>char</code> values) just prior to

      * execution of the <code>reverse</code> method. Then the

      * character at index <i>k</i> in the new character sequence is

      * equal to the character at index <i>n-k-1</i> in the old

      * character sequence.

      *

      * <p>Note that the reverse operation may result in producing

      * surrogate pairs that were unpaired low-surrogates and

      * high-surrogates before the operation. For example, reversing

      * "\uDC00\uD800" produces "\uD800\uDC00" which is

      * a valid surrogate pair.

      *

      * @return  a reference to this object.

      */

     public AbstractStringBuilder reverse() {

         boolean hasSurrogate = false;

         int n = count - 1;

         for (int j = (n-1) >> 1; j >= 0; --j) {

             char temp = value[j];

             char temp2 = value[n - j];

             if (!hasSurrogate) {

                 hasSurrogate = (temp >= Character.MIN_SURROGATE && temp <= Character.MAX_SURROGATE)

                     || (temp2 >= Character.MIN_SURROGATE && temp2 <= Character.MAX_SURROGATE);

             }

             value[j] = temp2;

             value[n - j] = temp;

         }

         if (hasSurrogate) {

             // Reverse back all valid surrogate pairs

             for (int i = 0; i < count - 1; i++) {

                 char c2 = value[i];

                 if (Character.isLowSurrogate(c2)) {

                     char c1 = value[i + 1];

                     if (Character.isHighSurrogate(c1)) {

                         value[i++] = c1;

                         value[i] = c2;

                     }

                 }

             }

         }

         return this;

     }

     /**

      * Returns a string representing the data in this sequence.

      * A new <code>String</code> object is allocated and initialized to

      * contain the character sequence currently represented by this

      * object. This <code>String</code> is then returned. Subsequent

      * changes to this sequence do not affect the contents of the

      * <code>String</code>.

      *

      * @return  a string representation of this sequence of characters.

      */

     public abstract String toString();

     /**

      * Needed by <tt>String</tt> for the contentEquals method.

      */

     final char[] getValue() {

         return value;

     }

     static char[] copyOfRange(char[] original, int from, int to) {

         int newLength = to - from;

         if (newLength < 0) {

             throw new IllegalArgumentException(from + " > " + to);

         }

         char[] copy = new char[newLength];

         System.arraycopy(original, from, copy, 0, Math.min(original.length - from, newLength));

         return copy;

     }

     // access system property

     static String getProperty(String nm) {

         return null;

     }

     static char[] copyOf(char[] original, int newLength) {

         char[] copy = new char[newLength];

         System.arraycopy(original, 0, copy, 0, Math.min(original.length, newLength));

         return copy;

     }

 }