AbstractStringBuilder源码学习

abstract class AbstractStringBuilder implements Appendable, CharSequence {

char[] value;

//当前字符个数
int count;

AbstractStringBuilder() {
}

AbstractStringBuilder(int capacity) {
value = new char[capacity];
}

//当前字符个数
public int length() {
return count;
}

//当前字符数组的容量
public int capacity() {
return value.length;
}

//扩容,扩容后的容量是原容量的两倍加2或者是请求容量中的最大值
public void ensureCapacity(int minimumCapacity) {
if (minimumCapacity > 0)
ensureCapacityInternal(minimumCapacity);
}

//没有被同步的扩容方法
private void ensureCapacityInternal(int minimumCapacity) {
// overflow-conscious code
if (minimumCapacity - value.length > 0)
expandCapacity(minimumCapacity);
}

/**
* 扩容
* 新容量 = 当前字符数 * 2 + 2;
*
* @param minimumCapacity
*/
void expandCapacity(int minimumCapacity) {
int newCapacity = value.length * 2 + 2;
//如果新容量 > 所需容量,则扩容为新容量
//如果新容量 < 所需容量,则扩容为所需容量
if (newCapacity - minimumCapacity < 0)
newCapacity = minimumCapacity;
//如果新容量小于0,说明整数溢出
if (newCapacity < 0) {
if (minimumCapacity < 0) // overflow
throw new OutOfMemoryError();
//扩容为最大值
newCapacity = Integer.MAX_VALUE;
}
value = Arrays.copyOf(value, newCapacity);
}

//减小数组的容量为当前字符个数
public void trimToSize() {
if (count < value.length) {
value = Arrays.copyOf(value, count);
}
}

//设置字符数组的长度为指定长度,多出的位用'\0'补上
public void setLength(int newLength) {
if (newLength < 0)
throw new StringIndexOutOfBoundsException(newLength);
//注意:这里进行一次扩容!!!因此新容量可能是原容量的两倍加2,也可能是指定的长度
ensureCapacityInternal(newLength);

if (count < newLength) {
Arrays.fill(value, count, newLength, '\0');
}
//注意:调用这个方法后字符数组中的字符数为指定的长度
count = newLength;
}

//返回指定位置的字符
@Override
public char charAt(int index) {
if ((index < 0) || (index >= count))
throw new StringIndexOutOfBoundsException(index);
return value[index];
}

//返回指定位置字符的字符编码
public int codePointAt(int index) {
if ((index < 0) || (index >= count)) {
throw new StringIndexOutOfBoundsException(index);
}
return Character.codePointAtImpl(value, index, count);
}

//返回指定位置字符的前一个字符的字符编码
public int codePointBefore(int index) {
int i = index - 1;
if ((i < 0) || (i >= count)) {
throw new StringIndexOutOfBoundsException(index);
}
return Character.codePointBeforeImpl(value, index, 0);
}

public int codePointCount(int beginIndex, int endIndex) {
if (beginIndex < 0 || endIndex > count || beginIndex > endIndex) {
throw new IndexOutOfBoundsException();
}
return Character.codePointCountImpl(value, beginIndex, endIndex-beginIndex);
}

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}. The first character to
* be copied is at index {@code srcBegin}; the last character to
* be copied is at index {@code srcEnd-1}. The total number of
* characters to be copied is {@code srcEnd-srcBegin}. The
* characters are copied into the subarray of {@code dst} starting
* at index {@code dstBegin} and ending at index:
* <pre>{@code
* dstbegin + (srcEnd-srcBegin) - 1
* }</pre>
*
* @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}.
* @throws     IndexOutOfBoundsException  if any of the following is true:
*             <ul>
*             <li>{@code srcBegin} is negative
*             <li>{@code dstBegin} is negative
*             <li>the {@code srcBegin} argument is greater than
*             the {@code srcEnd} argument.
*             <li>{@code srcEnd} is greater than
*             {@code this.length()}.
*             <li>{@code dstBegin+srcEnd-srcBegin} is greater than
*             {@code dst.length}
*             </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
168cc
(srcBegin > srcEnd)
throw new StringIndexOutOfBoundsException("srcBegin > srcEnd");
System.arraycopy(value, srcBegin, dst, dstBegin, srcEnd - srcBegin);
}

//将位于index的字符设置为指定的字符
public void setCharAt(int index, char ch) {
if ((index < 0) || (index >= count))
throw new StringIndexOutOfBoundsException(index);
value[index] = ch;
}

public AbstractStringBuilder append(Object obj) {
return append(String.valueOf(obj));
}

public AbstractStringBuilder append(String str) {
if (str == null)
return appendNull();
int len = str.length();
//扩容
ensureCapacityInternal(count + len);

//append字符串
str.getChars(0, len, value, count);
//重新设置字符串长度
count += len;
return this;
}

// Documentation in subclasses because of synchro difference
public AbstractStringBuilder append(StringBuffer sb) {
if (sb == null)
return appendNull();
int len = sb.length();
ensureCapacityInternal(count + len);
sb.getChars(0, len, value, count);
count += len;
return this;
}

AbstractStringBuilder append(AbstractStringBuilder asb) {
if (asb == null)
return appendNull();
int len = asb.length();
ensureCapacityInternal(count + len);
asb.getChars(0, len, value, count);
count += len;
return this;
}

// Documentation in subclasses because of synchro difference
@Override
public AbstractStringBuilder append(CharSequence s) {
if (s == null)
return appendNull();
if (s instanceof String)
return this.append((String)s);
if (s instanceof AbstractStringBuilder)
return this.append((AbstractStringBuilder)s);

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

private AbstractStringBuilder appendNull() {
int c = count;
ensureCapacityInternal(c + 4);
final char[] value = this.value;
value[c++] = 'n';
value[c++] = 'u';
value[c++] = 'l';
value[c++] = 'l';
count = c;
return this;
}

@Override
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;
}

public AbstractStringBuilder append(char[] str) {
int len = str.length;
ensureCapacityInternal(count + len);
System.arraycopy(str, 0, value, count, len);
count += len;
return this;
}

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;
}

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;
}

@Override
public AbstractStringBuilder append(char c) {
ensureCapacityInternal(count + 1);
value[count++] = c;
return this;
}

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;
}

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;
}

public AbstractStringBuilder append(float f) {
FloatingDecimal.appendTo(f,this);
return this;
}

public AbstractStringBuilder append(double d) {
FloatingDecimal.appendTo(d,this);
return this;
}

/**
* 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} at the specified position in this
* sequence. This sequence is shortened by one {@code char}.
*
* <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}s to remove by calling
* {@code Character.charCount(thisSequence.codePointAt(index))},
* where {@code thisSequence} is this sequence.
*
* @param       index  Index of {@code char} to remove
* @return      This object.
* @throws      StringIndexOutOfBoundsException  if the {@code index}
*              is negative or greater than or equal to
*              {@code length()}.
*/
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}. 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. First the
* characters in the substring are removed and then the specified
* {@code String} is inserted at {@code start}. (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}
*             is negative, greater than {@code length()}, or
*             greater than {@code end}.
*/
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} 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} 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
*
* <pre>{@code
* sb.subSequence(begin, end)}</pre>
*
* behaves in exactly the same way as the invocation
*
* <pre>{@code
* sb.substring(begin, end)}</pre>
*
* This method is provided so that this class can
* implement the {@link CharSequence} interface.
*
* @param      start   the start index, inclusive.
* @param      end     the end index, exclusive.
* @return     the specified subsequence.
*
* @throws  IndexOutOfBoundsException
*          if {@code start} or {@code end} are negative,
*          if {@code end} is greater than {@code length()},
*          or if {@code start} is greater than {@code end}
* @spec JSR-51
*/
@Override
public CharSequence subSequence(int start, int end) {
return substring(start, end);
}

/**
* Returns a new {@code String} that contains a subsequence of
* characters currently contained in this sequence. The
* substring begins at the specified {@code start} and
* extends to the character at index {@code end - 1}.
*
* @param      start    The beginning index, inclusive.
* @param      end      The ending index, exclusive.
* @return     The new string.
* @throws     StringIndexOutOfBoundsException  if {@code start}
*             or {@code end} are negative or greater than
*             {@code length()}, or {@code start} is
*             greater than {@code end}.
*/
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:
* <pre>{@code
* this.toString().startsWith(str, <i>k</i>)
* }</pre>
* is {@code true}.
*
* @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} is returned.
*/
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 {@code k} for which:
* <pre>{@code
*     k >= Math.min(fromIndex, this.length()) &&
*                   this.toString().startsWith(str, k)
* }</pre>
* 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.
*/
public int indexOf(String str, int fromIndex) {
return String.indexOf(value, 0, count, 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()}.
* The returned index is the largest value <i>k</i> such that
* <pre>{@code
* this.toString().startsWith(str, k)
* }</pre>
* 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} is returned.
*/
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:
* <pre>{@code
*     k <= Math.min(fromIndex, this.length()) &&
*                   this.toString().startsWith(str, k)
* }</pre>
* 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.
*/
public int lastIndexOf(String str, int fromIndex) {
return String.lastIndexOf(value, 0, count, str, 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} values) just prior to
* execution of the {@code reverse} 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
* "\u005CuDC00\u005CuD800" produces "\u005CuD800\u005CuDC00" which is
* a valid surrogate pair.
*
* @return  a reference to this object.
*/
public AbstractStringBuilder reverse() {
boolean hasSurrogates = false;
int n = count - 1;
for (int j = (n-1) >> 1; j >= 0; j--) {
int k = n - j;
char cj = value[j];
char ck = value[k];
value[j] = ck;
value[k] = cj;
if (Character.isSurrogate(cj) ||
Character.isSurrogate(ck)) {
hasSurrogates = true;
}
}
if (hasSurrogates) {
reverseAllValidSurrogatePairs();
}
return this;
}

/** Outlined helper method for reverse() */
private void reverseAllValidSurrogatePairs() {
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;
}
}
}
}

/**
* Returns a string representing the data in this sequence.
* A new {@code String} object is allocated and initialized to
* contain the character sequence currently represented by this
* object. This {@code String} is then returned. Subsequent
* changes to this sequence do not affect the contents of the
* {@code String}.
*
* @return  a string representation of this sequence of characters.
*/
@Override
public abstract String toString();

/**
* Needed by {@code String} for the contentEquals method.
*/
final char[] getValue() {
return value;
}

}