java.lang.Object
- java.lang.StringBuilder

All implemented interfaces

Serializable ， Appendable ， CharSequence ， Comparable<StringBuilder>
```
public final class StringBuilder
extends Object
implements Serializable, Comparable<StringBuilder>, CharSequence
```
A mutable sequence of characters. This class provides an API compatible withStringBufferCompatible API, but synchronization is not guaranteed. This class is designed to be used asStringBufferA replacement for places where a string buffer is used by a single thread (the usual case). Where possible, it is recommended to use this class in preference toStringBufferbecause it will be faster in most implementations.
StringBuilderThe main operation on it isappendandinsertmethods, which are overloaded to accept any type of data. Each effectively converts the given data to a string, then appends or inserts the characters of that string into the string builder. appendmethod always appends these characters at the end of the builder; insertThe method adds characters at the specified point.

For example, ifzrefers to its current contents as “startthe string builder object, then the method callz.append("le")will cause the string builder to contain “startle”, andz.insert(4, "le")Will change the string builder to containstarlet ”。

In general, if one is referring to an instanceStringBuilder, thensb.append(x)has the same effectsb.insert(sb.length(), x) 。

Each string builder has a capacity. As long as the length of the character sequence contained in the string builder does not exceed the capacity, it is not necessary to allocate a new internal buffer. If the internal buffer overflows, it automatically becomes larger.

StringBuilderInstances are not suitable for multi-threaded use. If such synchronization is required, it is recommended to useStringBuffer 。

Unless otherwise specified, it willnullparameter passed tonullthe constructor or method in ... will cause ... to be thrown.NullPointerException 。

API Note:

StringBuilderImplementationComparablebut does not overrideequals 。 Therefore,StringBuilderThe natural ordering is inconsistent with equals. ifStringBuilderobject used asStringBuilderkey in orSortedMapelements,SortedSet 。 seeComparable ， SortedMap, orSortedSetFor more information.

Starting from the following version:

1.5

See also:

StringBuffer ， String ， Serialized Form

Constructor Summary

Constructor
Constructor	Description
`StringBuilder()`	Constructs a string builder with no characters and an initial capacity of 16 characters.
`StringBuilder(int capacity)`	Constructs a string builder with no characters in it and with`capacity`The initial capacity specified by the parameter.
`StringBuilder(CharSequence seq)`	Constructs a string builder that contains the same ... as the specified`CharSequence`the same character.
`StringBuilder(String str)`	Constructs a string builder initialized to the contents of the specified string.

Method Summary

All methods Instance Methods Specific Methods
Variables and types	Methods	Description
`StringBuilder`	`append(boolean b)`	will`boolean`Appends the string representation of the argument to the sequence.
`StringBuilder`	`append(char c)`	will`char`Appends the string representation of the argument to this sequence.
`StringBuilder`	`append(char[] str)`	will`char`The string representation of the array argument is appended to this sequence.
`StringBuilder`	`append(char[] str, int offset, int len)`	will`char`Appends the string representation of a subarray of the array argument to this sequence.
`StringBuilder`	`append(double d)`	will`double`Appends the string representation of the argument to this sequence.
`StringBuilder`	`append(float f)`	will`float`Appends the string representation of the argument to this sequence.
`StringBuilder`	`append(int i)`	will`int`Appends the string representation of the argument to this sequence.
`StringBuilder`	`append(long lng)`	will`long`Appends the string representation of the argument to this sequence.
`StringBuilder`	`append(CharSequence s)`	Appends the specified character sequence to this`Appendable` 。
`StringBuilder`	`append(CharSequence s, int start, int end)`	the specified`CharSequence`The sequence is appended to this sequence.
`StringBuilder`	`append(Object obj)`	Append`Object`The string representation of the argument.
`StringBuilder`	`append(String str)`	Appends the specified string to this character sequence.
`StringBuilder`	`append(StringBuffer sb)`	the specified`StringBuffer`Appends to this sequence.
`StringBuilder`	`appendCodePoint(int codePoint)`	will`codePoint`Appends the string representation of the argument to this sequence.
`int`	`capacity()`	Returns the current capacity.
`char`	`charAt(int index)`	Returns the character at the specified index in this sequence`char`value.
`IntStream`	`chars()`	return`int`a stream of the elements in this sequence`char`The value is zero-extended.
`int`	`codePointAt(int index)`	Returns the character (Unicode code point) at the specified index.
`int`	`codePointBefore(int index)`	Returns the character (Unicode code point) before the specified index.
`int`	`codePointCount(int beginIndex, int endIndex)`	Returns the number of Unicode code points in the specified text range of this sequence.
`IntStream`	`codePoints()`	Returns a stream of code point values from this sequence.
`int`	`compareTo(StringBuilder another)`	`StringBuilder`Compares two sequences lexicographically`StringBuilder`instance.
`StringBuilder`	`delete(int start, int end)`	Deletes the characters in a substring of this sequence.
`StringBuilder`	`deleteCharAt(int index)`	Removes from this list the element at the specified position`char` 。
`void`	`ensureCapacity(int minimumCapacity)`	Ensures that the capacity is at least equal to the specified minimum.
`void`	`getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)`	Copies characters from this sequence to the destination character array.`dst` 。
`int`	`indexOf(String str)`	Returns the index within the string of the first occurrence of the specified substring.
`int`	`indexOf(String str, int fromIndex)`	Returns the index within the string of the first occurrence of the specified substring, starting at the specified index.
`StringBuilder`	`insert(int offset, boolean b)`	will`boolean`Inserts the string representation of the argument into this sequence.
`StringBuilder`	`insert(int offset, char c)`	will`char`Inserts the string representation of the argument into this sequence.
`StringBuilder`	`insert(int offset, char[] str)`	will`char`The string representation of the array argument is inserted into this sequence.
`StringBuilder`	`insert(int index, char[] str, int offset, int len)`	will`str`Inserts the string representation of a subarray of the array argument into this sequence.
`StringBuilder`	`insert(int offset, double d)`	will`double`Inserts the string representation of the argument into this sequence.
`StringBuilder`	`insert(int offset, float f)`	will`float`Inserts the string representation of the argument into this sequence.
`StringBuilder`	`insert(int offset, int i)`	the second`int`Inserts the string representation of the argument into this sequence.
`StringBuilder`	`insert(int offset, long l)`	will`long`Inserts the string representation of the argument into this sequence.
`StringBuilder`	`insert(int dstOffset, CharSequence s)`	the specified`CharSequence`inserted into this sequence.
`StringBuilder`	`insert(int dstOffset, CharSequence s, int start, int end)`	the specified`CharSequence`Inserts the sequence into this sequence.
`StringBuilder`	`insert(int offset, Object obj)`	will`Object`The string representation of the argument is inserted into this character sequence.
`StringBuilder`	`insert(int offset, String str)`	Inserts the string into this character sequence.
`int`	`lastIndexOf(String str)`	Returns the index within the string of the last occurrence of the specified substring.
`int`	`lastIndexOf(String str, int fromIndex)`	Returns the index within the string of the last occurrence of the specified substring, searching backward from the specified index.
`int`	`length()`	Returns the length (number of characters).
`int`	`offsetByCodePoints(int index, int codePointOffset)`	Returns the index in this sequence that starts from the given`index`Offset`codePointOffset`code point.
`StringBuilder`	`replace(int start, int end, String str)`	using the specified`String`characters replace the characters in a substring of this sequence.
`StringBuilder`	`reverse()`	This character sequence is caused by the reverse replacement of the sequence.
`void`	`setCharAt(int index, char ch)`	The character at the specified index is set to`ch` 。
`void`	`setLength(int newLength)`	Sets the length of the character sequence.
`CharSequence`	`subSequence(int start, int end)`	Returns a new character sequence that is a subsequence of this sequence.
`String`	`substring(int start)`	returns a new`String`, which contains a subsequence of the characters currently contained in this character sequence.
`String`	`substring(int start, int end)`	returns a new`String`, containing a subsequence of the characters currently contained in this sequence.
`void`	`trimToSize()`	Attempt to reduce the storage space used for the character sequence.

Class java.lang. declaring methodsObject
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Interface java.lang. declaring methodsCharSequence
charAt, chars, codePoints, length, subSequence, toString

- Constructor Detail
  - StringBuilder
```
public StringBuilder()
```
    Constructs a string builder with no characters and an initial capacity of 16 characters.
  - StringBuilder
```
public StringBuilder(int capacity)
```
    Constructs a string builder that contains no characters andcapacityThe initial capacity specified by the parameter.
    
    Parameter
    
    capacity- The initial capacity.
    
    Exception
    
    NegativeArraySizeException- ifcapacitythe argument is less than0 。
  - StringBuilder
```
public StringBuilder(String str)
```
    Constructs a string builder initialized to the contents of the specified string. The initial capacity of the string builder is16plus the length of the string argument.
    
    Parameter
    
    str- The initial contents of the buffer.
  - StringBuilder
```
public StringBuilder(CharSequence seq)
```
    Constructs a string builder that contains the same ... as the specifiedCharSequencethe same character. The initial capacity of the string builder is16addCharSequencethe length of the argument.
    
    Parameter
    
    seq- The sequence to be copied.
- Method Detail
  - compareTo
```
public int compareTo(StringBuilder another)
```
    StringBuilderCompares two sequences lexicographicallyStringBuilderinstance. This method followsCharSequence.compare(this, another)The same rules of dictionary comparison as defined in the method.
    For fine-grained, locale-sensitive string comparison, seeCollator 。
    
    Specified by:
    
    compareToIn the interfaceComparable<StringBuilder>
    
    Parameter
    
    another- the object to be compared with.StringBuilder
    
    Result
    
    Value0if thisStringBuildercontains the same characters as the parameterStringBuilderthe same character sequence; if thisStringBuilderlexicographically less thanStringBuilderparameters,StringBuildera negative integer; if thisStringBuilderlexicographically greater thanStringBuilderparameters,StringBuildera positive integer.
    
    Starting from the following version:
    
    11
  - append
```
public StringBuilder append(Object obj)
```
    AppendObjectThe string representation of the argument.
    The overall effect with the methodString.valueOf(Object)Converts the argument to a stringexactly the same, and then the characters of the string areappended 。
    
    Parameter
    
    obj - Object 。
    
    Result
    
    A reference to this object.
  - append
```
public StringBuilder append(String str)
```
    Appends the specified string to this character sequence.
    Appends in orderStringThe characters of the argument are appended, increasing the length of this sequence by the length of the argument. ifstrYesnull, then append four characters"null" 。
    
    designnis performedappendthe length of this character sequence before the method. ifkless thann, then the index in the new character sequencekthe character at ... is equal to the character at index ... in the old character sequence.kcharacter at; Otherwise, it is equal to the parameter.strindex inkncharacter at.
    
    Parameter
    
    str- a string.
    
    Result
    
    A reference to this object.
  - append
```
public StringBuilder append(StringBuffer sb)
```
    the specifiedStringBufferAppends to this sequence.
    StringBufferThe characters of the argument are appended to this sequence in order, increasing the length of this sequence by the length of the argument. ifsbYesnull, then the four characters"null"appended to this sequence.
    
    designnis performedappendthe length of this character sequence before the method. ifkless thann, then the index in the new character sequencekthe character at ... is equal to the character at index ... in the old character sequence.kcharacter at; Otherwise, it is equal to the parameter.sbindex inkncharacter at.
    
    Parameter
    
    sb- To be appended.StringBuffer 。
    
    Result
    
    A reference to this object.
  - append
```
public StringBuilder append(CharSequence s)
```
    Instructions copied from the interface:Appendable
    
    Appends the specified character sequence to thisAppendable 。
    according to which class implements the character sequencecsq, may not append the entire sequence. For example, ifcsqYesCharBuffer，the subsequence to be appended is defined by the buffer's position and limit.
    
    Specified by:
    
    appendIn the interfaceAppendable
    
    Parameter
    
    s- the character sequence to be appended. ifcsqYesnull, then the four characters"null"Will be appended to this Appendable.
    
    Result
    
    ReferenceAppendable
  - append
```
public StringBuilder append(CharSequence s,
                            int start,
                            int end)
```
    the specifiedCharSequenceThe sequence is appended to this sequence.
    from indexstartthe start parametersCharacters are appended to the contents of this sequence in order, up to the index (exclusive)end 。 The length of the sequence is increased by the value.end - start 。
    
    designnis performedappendthe length of this character sequence before the method. then, ifkless thann, then the index in the character sequenceAt kthe character becomes equal to the index in this sequencekcharacter at; Otherwise, it is equal to the parameter.sindex ink + start-nAt thes 。
    
    ifsYesnull, then this method appends characters as if the s parameter were a string containing four characters"null"sequence of"null" 。
    
    Specified by:
    
    appendIn the interfaceAppendable
    
    Parameter
    
    s- the sequence to be appended.
    
    startThe starting index of the subsequence to append.
    
    endThe ending index of the subsequence to append.
    
    Result
    
    A reference to this object.
    
    Exception
    
    IndexOutOfBoundsException- ifstartis negative, orstartgreater thanendorendgreater thans.length()
  - append
```
public StringBuilder append(char[] str)
```
    willcharThe string representation of the array argument is appended to this sequence.
    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.
    
    The overall effect is just as if through the methodString.valueOf(char[])Converts the argument to a stringSame, and the characters of that string are then those of this character sequenceappended 。
    
    Parameter
    
    str- the character to be appended.
    
    Result
    
    A reference to this object.
  - append
```
public StringBuilder append(char[] str,
                            int offset,
                            int len)
```
    willcharAppends the string representation of a subarray of the array argument to this sequence.
    from indexoffsetstartingcharArraystrThe characters are appended to the contents of this sequence in order. The value of the length increase of this sequencelen 。
    
    The overall effect is just as if through the methodString.valueOf(char[],int,int)Converts the argument to a stringSame, and the characters of the string for this character sequenceThen isappended 。
    
    Parameter
    
    str- the character to be appended.
    
    offset- the first character to be appended.charthe index of.
    
    len- To be appended.charthe number of.
    
    Result
    
    A reference to this object.
    
    Exception
    
    IndexOutOfBoundsException- if it isoffset < 0orlen < 0oroffset+len > str.length
  - append
```
public StringBuilder append(boolean b)
```
    willbooleanAppends the string representation of the argument to the sequence.
    The overall effect is just as if through the methodString.valueOf(boolean)Converts the argument to a stringSame, and the characters of that string are then those of this character sequenceappended 。
    
    Parameter
    
    b - boolean 。
    
    Result
    
    A reference to this object.
  - append
```
public StringBuilder append(char c)
```
    willcharAppends the string representation of the argument to this sequence.
    The argument is appended to the contents of this sequence. The length of this sequence increases1 。
    
    The overall effect is just as if through the methodString.valueOf(char)Converts the argument to a stringSameand the characters in the string are subsequently those of the character sequenceappended 。
    
    Specified by:
    
    appendIn the interfaceAppendable
    
    Parameter
    
    c - a char 。
    
    Result
    
    A reference to this object.
  - append
```
public StringBuilder append(int i)
```
    willintAppends the string representation of the argument to this sequence.
    The overall effect with the methodString.valueOf(int)Converts the argument to a stringexactly the same, and then the characters of the string areappended 。
    
    Parameter
    
    i - int 。
    
    Result
    
    A reference to this object.
  - append
```
public StringBuilder append(long lng)
```
    willlongAppends the string representation of the argument to this sequence.
    The overall effect with the methodString.valueOf(long)Converts the argument to a stringexactly the same, and then the characters of the string areappended 。
    
    Parameter
    
    lng - long 。
    
    Result
    
    A reference to this object.
  - append
```
public StringBuilder append(float f)
```
    willfloatAppends the string representation of the argument to this sequence.
    The overall effect is just as if through the methodString.valueOf(float)Converts the argument to a stringSame, and the characters of that string are then those of this character sequenceappended 。
    
    Parameter
    
    f - a float 。
    
    Result
    
    A reference to this object.
  - append
```
public StringBuilder append(double d)
```
    willdoubleAppends the string representation of the argument to this sequence.
    The overall effect is just as if through the methodString.valueOf(double)Converts the argument to a stringSame, and the characters of that string are then those of this character sequenceappended 。
    
    Parameter
    
    d - a double 。
    
    Result
    
    A reference to this object.
  - appendCodePoint
```
public StringBuilder appendCodePoint(int codePoint)
```
    willcodePointAppends the string representation of the argument to this sequence.
    The argument is appended to the contents of this sequence. The length of this sequence increasesCharacter.charCount(codePoint) 。
    
    The overall effect is just as if through the methodCharacter.toChars(int)converts the argument tocharsame as the array, and the characters in the arrayThen isappended 。
    
    Parameter
    
    codePoint- Unicode code point
    
    Result
    
    A reference to this object.
    
    Starting from the following version:
    
    1.5
  - delete
```
public StringBuilder delete(int start,
                            int end)
```
    Deletes the characters in a substring of this sequence. Substring from the specifiedstartbegins, and if no such character exists, then extends to the indexend - 1the character at, or the end of, the sequence. ifstartequalsend, then no changes are made.
    
    Parameter
    
    start- the starting index, inclusive.
    
    end- the ending index, exclusive.
    
    Result
    
    this object.
    
    Exception
    
    StringIndexOutOfBoundsException- ifstartis negative, greater thanlength(), or greater thanend 。
  - deleteCharAt
```
public StringBuilder deleteCharAt(int index)
```
    Removes from this list the element at the specified positionchar 。 the sequence consists of acharshortened.
    Note: If the character at the given index is a supplementary character, this method does not delete the entire character. If you need to correctly handle supplementary characters, callCharacter.charCount(thisSequence.codePointAt(index))determines what is to be deletedcharthe number of s, wherethisSequenceis this sequence.
    
    Parameter
    
    index- the index number to be deleted.char
    
    Result
    
    this object.
    
    Exception
    
    StringIndexOutOfBoundsException- ifindexis negative or greater than or equal to.length() 。
  - replace
```
public StringBuilder replace(int start,
                             int end,
                             String str)
```
    using the specifiedStringcharacters replace the characters in a substring of this sequence. Substring from the specifiedstartstarts, if no such character exists, extends to the indexend - 1the character at, or the end of, the sequence. First remove the characters in the substring, then atStringInserts the specifiedstart 。 (If necessary, this sequence will be extended to accommodate the specified string.)
    
    Parameter
    
    start- the starting index, inclusive.
    
    end- the ending index, exclusive.
    
    str- the string that replaces the previous contents.
    
    Result
    
    this object.
    
    Exception
    
    StringIndexOutOfBoundsException- ifstartis negative, greater thanlength(), or greater thanend 。
  - insert
```
public StringBuilder insert(int index,
                            char[] str,
                            int offset,
                            int len)
```
    willstrInserts the string representation of a subarray of the array argument into this sequence. subarray from the specifiedoffsetstarts, and extendslen char s。 the characters of the subarray are inindexinsert into this sequence at the indicated position. The length of this sequence increaseslen char s。
    
    Parameter
    
    index- the position at which to insert the subarray.
    
    str - chararray.
    
    offset- the first character in the subarray to be inserted.charthe index of.
    
    len- in the subarray to be inserted.charthe number of s.
    
    Result
    
    this object
    
    Exception
    
    StringIndexOutOfBoundsException- ifindexis negative or greater thanlength(), oroffsetorlenis negative, or(offset+len)greater thanstr.length 。
  - insert
```
public StringBuilder insert(int offset,
                            Object obj)
```
    willObjectThe string representation of the argument is inserted into this character sequence.
    the overall effect is the same as if the second argument were passed through the method.String.valueOf(Object)converted to a stringexactly the same, and the character of this string in the character sequence at the specified offset isinserted 。
    
    offsetThe argument must be greater than or equal to0, and is less than or equal to this sequence'slength 。
    
    Parameter
    
    offset- The offset.
    
    obj - Object 。
    
    Result
    
    A reference to this object.
    
    Exception
    
    StringIndexOutOfBoundsException- if the offset is invalid.
  - insert
```
public StringBuilder insert(int offset,
                            String str)
```
    Inserts the string into this character sequence.
    StringThe characters of the argument are inserted into this sequence at the specified offset in order, shifting any characters originally above that position upward, and increasing the length of this sequence by the length of the argument. ifstrYesnull, then the four characters"null"Inserted into this sequence.
    
    Index in the new character sequencekthe character at the position is equal to:
    
    ifkless thanoffset, then the index in the old character sequencekthe character at
    
    Parameterstrthe index withink -offsetthe characters, ifknot less thanoffsetbut less thanoffset+str.length()
    
    the index in the old character sequence isk -str.length()the characters, ifknot less thanoffset+str.length()
    
    offsetThe argument must be greater than or equal to0, and is less than or equal to this sequence'slength 。
    Parameter
    
    offset- The offset.
    
    str- a string.
    
    Result
    
    A reference to this object.
    
    Exception
    
    StringIndexOutOfBoundsException- if the offset is invalid.
  - insert
```
public StringBuilder insert(int offset,
                            char[] str)
```
    willcharThe string representation of the array argument is inserted into this sequence.
    The characters of the array argument atoffsetat the indicated position into the contents of this sequence. The length of this sequence increases by the length of the argument.
    
    The overall effect is as if the second argument were passed through the methodString.valueOf(char[])converted to a stringSameand the characters of this string at the specified offset are those of the character sequenceinserted 。
    
    offsetThe argument must be greater than or equal to0, and is less than or equal to this sequence'slength 。
    
    Parameter
    
    offset- The offset.
    
    str- The character array.
    
    Result
    
    A reference to this object.
    
    Exception
    
    StringIndexOutOfBoundsException- if the offset is invalid.
  - insert
```
public StringBuilder insert(int dstOffset,
                            CharSequence s)
```
    the specifiedCharSequenceinserted into this sequence.
    CharSequenceInserts the characters of the parameter into this sequence at the specified offset, shifting up any characters initially above that position, and increasing the length of this sequence by the length of parameter s.
    
    The result of this method is the same as calling this object'sinsertthe (dstOffset, s, 0, s.length()) methodexactly the same 。
    
    ifsYesnull, then the four characters"null"Inserts into this sequence.
    
    Parameter
    
    dstOffset- The offset.
    
    s- the sequence to be inserted
    
    Result
    
    A reference to this object.
    
    Exception
    
    IndexOutOfBoundsException- if the offset is invalid.
  - insert
```
public StringBuilder insert(int dstOffset,
                            CharSequence s,
                            int start,
                            int end)
```
    the specifiedCharSequenceInserts the sequence into this sequence.
    subsequence of the argumentsby specifyingstartandendare inserted at the specified destination offset in this sequence, moving up any characters originally above that position. the length of this sequence increases byend - start 。
    
    index in this sequencekthe character at the position becomes equal to:
    
    ifkless thandstOffset, then the index in this sequencekthe character at
    
    Parametersthe index withink +start-dstOffsetthe characters, ifkgreater than or equal todstOffsetbut less thandstOffset+end-start
    
    ifkgreater than or equal todstOffset+end-start, then the index in this sequence isk -(end-start)characters of
    
    dstOffsetThe argument must be greater than or equal to0, and less than or equal to this sequence'slength 。
    
    The start parameter must be non-negative and not greater thanend 。
    
    the end parameter must be greater than or equal tostart, and less than or equal to the length of s.
    
    ifsYesnull, then this method inserts characters as if the s parameter were a string containing four characters"null"sequence of"null" 。
    Parameter
    
    dstOffset- the offset in this sequence.
    
    s- the sequence to be inserted.
    
    startThe starting index of the subsequence to insert.
    
    endThe ending index of the subsequence to insert.
    
    Result
    
    A reference to this object.
    
    Exception
    
    IndexOutOfBoundsException- ifdstOffsetis negative or greater thanthis.length(), orstartorendis negative, orstartgreater thanendorendgreater thans.length()
  - insert
```
public StringBuilder insert(int offset,
                            boolean b)
```
    willbooleanInserts the string representation of the argument into this sequence.
    the overall effect is the same as if the second argument were passed through the method.String.valueOf(boolean)converted to a stringexactly the same, and the characters of that string are inserted into this character sequence at the specified offset, followed byinserted 。
    
    offsetThe argument must be greater than or equal to0, and is less than or equal to this sequence'slength 。
    
    Parameter
    
    offset- The offset.
    
    b - a boolean 。
    
    Result
    
    A reference to this object.
    
    Exception
    
    StringIndexOutOfBoundsException- if the offset is invalid.
  - insert
```
public StringBuilder insert(int offset,
                            char c)
```
    willcharInserts the string representation of the argument into this sequence.
    The overall effect is the same as through the methodString.valueOf(char)Converts the second argument to a stringexactly the same, and the characters of that string are inserted into that character sequence at the specified offset, followed byinserted 。
    
    offsetThe argument must be greater than or equal to0, and is less than or equal to this sequence'slength 。
    
    Parameter
    
    offset- The offset.
    
    c - a char 。
    
    Result
    
    A reference to this object.
    
    Exception
    
    IndexOutOfBoundsException- if the offset is invalid.
  - insert
```
public StringBuilder insert(int offset,
                            int i)
```
    the secondintInserts the string representation of the argument into this sequence.
    The overall effect is as if the second argument were passed through the methodString.valueOf(int)converted to a stringSameand the characters of this string are in the character sequence at the specified offsetinserted 。
    
    offsetThe argument must be greater than or equal to0, and less than or equal to this sequence'slength 。
    
    Parameter
    
    offset- The offset.
    
    i - int 。
    
    Result
    
    A reference to this object.
    
    Exception
    
    StringIndexOutOfBoundsException- if the offset is invalid.
  - insert
```
public StringBuilder insert(int offset,
                            long l)
```
    willlongInserts the string representation of the argument into this sequence.
    The overall effect is exactly the same as if the second argument were converted to a string by the methodString.valueOf(long), and the characters of the string theninsertedThe character sequence is formed at the indicated offset.
    
    offsetThe argument must be greater than or equal to0, and less than or equal to this sequence'slength 。
    
    Parameter
    
    offset- The offset.
    
    l - long 。
    
    Result
    
    A reference to this object.
    
    Exception
    
    StringIndexOutOfBoundsException- if the offset is invalid.
  - insert
```
public StringBuilder insert(int offset,
                            float f)
```
    willfloatInserts the string representation of the argument into this sequence.
    The overall effect is the same as through the methodString.valueOf(float)Converts the second argument to a stringexactly the same, and the character of this string in the character sequence at the specified offset isinserted 。
    
    offsetThe argument must be greater than or equal to0, and is less than or equal to this sequence'slength 。
    
    Parameter
    
    offset- The offset.
    
    f - float 。
    
    Result
    
    A reference to this object.
    
    Exception
    
    StringIndexOutOfBoundsException- if the offset is invalid.
  - insert
```
public StringBuilder insert(int offset,
                            double d)
```
    willdoubleInserts the string representation of the argument into this sequence.
    The overall effect is the same as through the methodString.valueOf(double)Converts the second argument to a stringexactly the same, and the character of this string in the character sequence at the specified offset isinserted 。
    
    offsetThe argument must be greater than or equal to0, and less than or equal to this sequence'slength 。
    
    Parameter
    
    offset- The offset.
    
    d - a double 。
    
    Result
    
    A reference to this object.
    
    Exception
    
    StringIndexOutOfBoundsException- if the offset is invalid.
  - indexOf
```
public int indexOf(String str)
```
    Returns the index within the string of the first occurrence of the specified substring.
    The returned index is the minimum valuek, where:
    
    this.toString().startsWith(str, k)
    if there is no such valuekexists, then-1returns.
    Parameter
    
    str- The substring to search for.
    
    Result
    
    The index of the first occurrence of the specified substring, or -1 if there is no such occurrence.-1 。
  - indexOf
```
public int indexOf(String str,
                   int fromIndex)
```
    Returns the index within the string of the first occurrence of the specified substring, starting at the specified index.
    The returned index is the minimum valuek, where:
    
    k >= Math.min(fromIndex, this.length()) && this.toString().startsWith(str, k)
    if there is no such valuekexists, then-1returns.
    Parameter
    
    str- The substring to search for.
    
    fromIndex- The index from which to start searching.
    
    Result
    
    The index of the first occurrence of the specified substring beginning at the specified index, or -1 if there is no such occurrence.-1 。
  - lastIndexOf
```
public int lastIndexOf(String str)
```
    Returns the index within the string of the last occurrence of the specified substring. The last occurrence of the empty string "" is considered to occur at the index valuethis.length() 。
    The returned index is the maximum valuek, where:
    
    this.toString().startsWith(str, k)
    if there is no such valuekexists, then-1returns.
    Parameter
    
    str- The substring to search for.
    
    Result
    
    The index of the last occurrence of the specified substring, or -1 if there is no such occurrence.-1 。
  - lastIndexOf
```
public int lastIndexOf(String str,
                       int fromIndex)
```
    Returns the index within the string of the last occurrence of the specified substring, searching backward from the specified index.
    The returned index is the maximum valuek, where:
    
    k <= Math.min(fromIndex, this.length()) && this.toString().startsWith(str, k)
    if there is no such valuekexists, then-1returns.
    Parameter
    
    str- The substring to search for.
    
    fromIndex- The index from which to start searching.
    
    Result
    
    the index of the last occurrence of the specified substring, searching backward from the specified index, if there is no such occurrence,-1 。
  - reverse
```
public StringBuilder reverse()
```
    This character sequence is caused by the reverse replacement of the sequence. If the sequence contains any surrogate pairs, these surrogate pairs are treated as a single character for the reverse operation. Therefore, the order of high and low surrogates will never be reversed. designnis performedreversethe character length of this character sequence before the method (notcharthe length in the value). Then, the index in the new character sequencekthe character at ... is equal to the character at index ... in the old character sequence.nk-1character at.
    Note that the reverse operation may result in producing surrogate pairs that were unpaired low and high surrogates before the operation. For example, reversing “\ uDC00 \ uD800” generates “\ uD800 \ uDC00”, which is a valid surrogate pair.
    
    Result
    
    A reference to this object.
  - length
```
public int length()
```
    Returns the length (number of characters).
    
    Specified by:
    
    lengthIn the interfaceCharSequence
    
    Result
    
    The length of the character sequence currently represented by this object.
  - capacity
```
public int capacity()
```
    Returns the current capacity. Capacity is the amount of storage available for newly inserted characters, beyond which allocation will occur.
    
    Result
    
    current capacity
  - ensureCapacity
```
public void ensureCapacity(int minimumCapacity)
```
    Ensures that the capacity is at least equal to the specified minimum. If the current capacity is less than the argument, a new internal array with a larger capacity is allocated. The new capacity is the larger of:
    
    minimumCapacityparameters.
    
    twice the old capacity, plus2 。
    
    ifminimumCapacityIf the parameter is non-positive, this method does nothing and simply returns. Note that subsequent operations on this object can reduce the actual capacity below the capacity requested here.
    Parameter
    
    minimumCapacity- the minimum capacity required.
  - trimToSize
```
public void trimToSize()
```
    Attempt to reduce the storage space 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 be more space efficient. Calling this method may (but is not required to) affect subsequent calls.capacity()the value returned by the method.
  - setLength
```
public void setLength(int newLength)
```
    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 non-negative index less thank newLength, at the index of the new character sequencekThe character at the position is the same at the old sequence index.kifkcharacters less than the length of the original character sequence; Otherwise, it is the null character'\u0000' 。 In other words, ifnewLengthIf the argument is less than the current length, then the length will be changed to the specified length.
    ifnewLengthIf the parameter is greater than or equal to the current length, then sufficient null characters ('\u0000'), so that length becomesnewLengthparameters.
    
    newLengthThe argument must be greater than or equal to0 。
    
    Parameter
    
    newLength- new length
    
    Exception
    
    IndexOutOfBoundsException- ifnewLengthThe parameter is negative.
  - charAt
```
public char charAt(int index)
```
    Returns the character at the specified index in this sequencecharvalue. firstcharvalue at index0, the next is at index1, and so on, as shown in the array indices.
    The index parameter must be greater than or equal to0, and less than the length of this sequence.
    
    if the index specifiedcharValue issurrogate, then a surrogate value is returned.
    
    Specified by:
    
    charAtIn the interfaceCharSequence
    
    Parameter
    
    index- requiredcharthe index of the value.
    
    Result
    
    at the specified indexcharvalue.
    
    Exception
    
    IndexOutOfBoundsException- ifindexis negative or greater than or equal to.length() 。
  - codePointAt
```
public int codePointAt(int index)
```
    Returns the character (Unicode code point) at the specified index. index referencecharvalue (Unicode code units), ranging from0toCharSequence.length() - 1 。
    If the specified at the given indexcharIf the value is in the high surrogate range, then the following index is less than the length of this sequence, and the value at the following indexcharIf the value is in the low-surrogate range, then the supplementary code point corresponding to this surrogate pair is returned. Otherwise, return the one at the given indexcharvalue.
    
    Parameter
    
    index - charthe index of the value
    
    Result
    
    indexthe code point value of the character at the specified index.
    
    Exception
    
    IndexOutOfBoundsException- ifindexThe argument is negative or not less than the length of this sequence.
  - codePointBefore
```
public int codePointBefore(int index)
```
    Returns the character (Unicode code point) before the specified index. index referencecharvalue (Unicode code units), ranging from1toCharSequence.length() 。
    ifcharAt value(index - 1)is in the low surrogate range,(index - 2)is not negative, andcharAt value(index - 2)is in the high surrogate range, then the supplementary code point value of the surrogate pair is returned. ifcharAt valueindex - 1If it is an unpaired low surrogate or a high surrogate, then the surrogate value is returned.
    
    Parameter
    
    index- the index following the code point to be returned.
    
    Result
    
    The Unicode code point value before the given index.
    
    Exception
    
    IndexOutOfBoundsException- ifindexThe argument is less than 1 or greater than the length of this sequence.
  - codePointCount
```
public int codePointCount(int beginIndex,
                          int endIndex)
```
    Returns the number of Unicode code points in the specified text range of this sequence. The text range starts at the specifiedbeginIndex, and extends tocharat indexendIndex - 1 。 Therefore, the length of the text range (incharin s) isendIndex-beginIndex 。 Unpaired surrogates in this sequence count as one code point each.
    
    Parameter
    
    beginIndex- the first character of the text range.charthe index of.
    
    endIndex- the last character of the text range.charthe index after.
    
    Result
    
    The number of Unicode code points in the specified text range.
    
    Exception
    
    IndexOutOfBoundsException- ifbeginIndexis negative, orendIndexgreater than the length of this sequence, orbeginIndexgreater thanendIndex 。
  - offsetByCodePoints
```
public int offsetByCodePoints(int index,
                              int codePointOffset)
```
    Returns the index in this sequence that starts from the givenindexOffsetcodePointOffsetcode point. indexandcodePointOffsetUnpaired surrogates in the given text range count as one code point each.
    
    Parameter
    
    index- the index to be offset.
    
    codePointOffset- the offset in code points.
    
    Result
    
    index in this sequence
    
    Exception
    
    IndexOutOfBoundsException- ifindexis negative or greater than the length of this sequence, or ifcodePointOffsetis positive and fromindexthe substring startingindexhas fewer thancodePointOffsetcode point, or ifcodePointOffsetis negative andindexthe substring beforeindexless than the absolute valuecodePointOffsetcode point.
  - getChars
```
public void getChars(int srcBegin,
                     int srcEnd,
                     char[] dst,
                     int dstBegin)
```
    Copy characters from this sequence into the destination character arraydst 。 The first character to be copied is the indexsrcBegin ; The last character to be copied is located at indexsrcEnd-1 。 the total number of characters to be copied issrcEnd-srcBegin 。 characters are copied todstOf subdstfrom indexdstBeginStarts at and ends at the index:
    dstbegin + (srcEnd-srcBegin) - 1
    Parameter
    
    srcBegin- Start copying at this offset.
    
    srcEnd- Stop copying at this offset.
    
    dst- The array into which the data is to be copied.
    
    dstBegin- offset todst 。
    
    Exception
    
    IndexOutOfBoundsException- if any of the following conditions is satisfied:
    
    srcBeginis negative
    
    dstBeginis negative
    
    srcBeginthe argument is greater thansrcEndparameters.
    
    srcEndgreater thanthis.length() 。
    
    dstBegin+srcEnd-srcBegingreater thandst.length
  - setCharAt
```
public void setCharAt(int index,
                      char ch)
```
    The character at the specified index is set toch 。 The sequence is altered to represent a new character sequence identical to the old character sequence, except that it contains located atchcharacters ofindex 。
    The index parameter must be greater than or equal to0, and less than the length of this sequence.
    
    Parameter
    
    index- the index of the character to be modified.
    
    ch- The new character.
    
    Exception
    
    IndexOutOfBoundsException- ifindexis negative or greater than or equal to.length() 。
  - substring
```
public String substring(int start)
```
    returns a newString, which contains a subsequence of the characters currently contained in this character sequence. The substring starts at the specified index and extends to the end of this sequence.
    
    Parameter
    
    start- the starting index, inclusive.
    
    Result
    
    - The new string.
    
    Exception
    
    StringIndexOutOfBoundsException- ifstartless than zero, or greater than the length of this object.
  - subSequence
```
public CharSequence subSequence(int start,
                                int end)
```
    Returns a new character sequence that is a subsequence of this sequence.
    The form of calling this method
    
    sb.subSequence(begin, end)
    The behavior is exactly the same as calling
    sb.substring(begin, end)
    This method is provided so that this class can implementCharSequenceInterface.
    Specified by:
    
    subSequenceIn the interfaceCharSequence
    
    Parameter
    
    start- the starting index, inclusive.
    
    end- the ending index, exclusive.
    
    Result
    
    the specified subsequence
    
    Exception
    
    IndexOutOfBoundsException- ifstartorendis negative, ifendgreater thanlength(), or ifstartgreater thanend
  - substring
```
public String substring(int start,
                        int end)
```
    returns a newString, containing a subsequence of the characters currently contained in this sequence. Substring from the specifiedstartstarts, and extends to the indexend - 1character at.
    
    Parameter
    
    start- the starting index, inclusive.
    
    end- the ending index, exclusive.
    
    Result
    
    - The new string.
    
    Exception
    
    StringIndexOutOfBoundsException- ifstartorendis negative or greater thanlength(), orstartgreater thanend 。
  - chars
```
public IntStream chars()
```
    returninta stream of the elements in this sequencecharThe value is zero-extended. any mapping toa character that is a surrogate code pointare all uninterpreted.
    When a terminal stream operation begins, the stream is bound to the sequence (specifically, for mutable sequences, the stream'sspliteratorYeslate-binding ）。 If the sequence is modified during the operation, the result is undefined.
    
    Specified by:
    
    charsIn the interfaceCharSequence
    
    Result
    
    An IntStream of char values from this sequence.
    
    Starting from the following version:
    
    9
  - codePoints
```
public IntStream codePoints()
```
    Returns a stream of code point values from this sequence. Any surrogate pairs encountered in the sequence are combined, just likesame as Character.toCodePoint, the result is passed to the stream. Any other code unit (including ordinary BMP characters, unpaired surrogates, and undefined code units) will be zero-extended tointthe value, then passed to the stream.
    When a terminal stream operation begins, the stream is bound to the sequence (specifically, for mutable sequences, the stream'sspliteratorYeslate-binding ）。 If the sequence is modified during the operation, the result is undefined.
    
    Specified by:
    
    codePointsIn the interfaceCharSequence
    
    Result
    
    The IntStream of Unicode code points points to this sequence.
    
    Starting from the following version:
    
    9

Class StringBuilder

Constructor Summary

Method Summary

Class java.lang. declaring methodsObject

Interface java.lang. declaring methodsCharSequence

Constructor Detail

StringBuilder

StringBuilder

StringBuilder

StringBuilder

Method Detail

compareTo

append

append

append

append

append

append

append

append

append

append

append

append

append

appendCodePoint

delete

deleteCharAt

replace

insert

insert

insert

insert

insert

insert

insert

insert

insert

insert

insert

insert

indexOf

indexOf

lastIndexOf

lastIndexOf

reverse

length

capacity

ensureCapacity

trimToSize

setLength

charAt

codePointAt

codePointBefore

codePointCount

offsetByCodePoints

getChars

setCharAt

substring

subSequence

substring

chars

codePoints