/*

 * 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

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.lang;

/**

 * 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 = String.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 = String.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) {

        if (i == Integer.MIN_VALUE) {

            append("-2147483648");

            return this;

        }

        int appendedLength = (i < 0) ? Integer.stringSize(-i) + 1

                                     : Integer.stringSize(i);

        int spaceNeeded = count + appendedLength;

        ensureCapacityInternal(spaceNeeded);

        Integer.getChars(i, spaceNeeded, value);

        count = spaceNeeded;

        return this;

    }

    /**

     * 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) {

        throw new UnsupportedOperationException();

    }

    /**

     * 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) {

        throw new UnsupportedOperationException();

    }

    /**

     * 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.

     *