public final class StringBuilder extends Object implements Serializable, CharSequence
A mutable sequence of characters. This class provides an API compatible with StringBuffer
, but with no guarantee of synchronization. This class is designed for use as a drop-in replacement for StringBuffer
in places where the string buffer was being used by a single thread (as is generally the case). Where possible, it is recommended that this class be used in preference to StringBuffer
as it will be faster under most implementations.
The principal operations on a StringBuilder
are the append
and insert
methods, which are overloaded so as to accept data of any type. Each effectively converts a given datum to a string and then appends or inserts the characters of that string to the string builder. The append
method always adds these characters at the end of the builder; the insert
method adds the characters at a specified point.
For example, if z
refers to a string builder object whose current contents are "start
", then the method call z.append("le")
would cause the string builder to contain "startle
", whereas z.insert(4, "le")
would alter the string builder to contain "starlet
".
In general, if sb refers to an instance of a StringBuilder
, then sb.append(x)
has the same effect as sb.insert(sb.length(), x)
.
Every 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 is automatically made larger.
Instances of StringBuilder
are not safe for use by multiple threads. If such synchronization is required then it is recommended that StringBuffer
be used.
Unless otherwise noted, passing a null
argument to a constructor or method in this class will cause a NullPointerException
to be thrown.
StringBuffer
, String
, Serialized Formpublic StringBuilder()
Constructs a string builder with no characters in it and an initial capacity of 16 characters.
public StringBuilder(int capacity)
Constructs a string builder with no characters in it and an initial capacity specified by the capacity
argument.
capacity
- the initial capacity.NegativeArraySizeException
- if the capacity
argument is less than 0
.public StringBuilder(String str)
Constructs a string builder initialized to the contents of the specified string. The initial capacity of the string builder is 16
plus the length of the string argument.
str
- the initial contents of the buffer.public StringBuilder(CharSequence seq)
Constructs a string builder that contains the same characters as the specified CharSequence
. The initial capacity of the string builder is 16
plus the length of the CharSequence
argument.
seq
- the sequence to copy.public StringBuilder append(Object obj)
Appends the string representation of the Object
argument.
The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(Object)
, and the characters of that string were then appended
to this character sequence.
obj
- an Object
.public StringBuilder append(String str)
Appends the specified string to this character sequence.
The characters of the String
argument are appended, in order, increasing the length of this sequence by the length of the argument. If str
is null
, then the four characters "null"
are appended.
Let n be the length of this character sequence just prior to execution of the append
method. Then the character at index k in the new character sequence is equal to the character at index k in the old character sequence, if k is less than n; otherwise, it is equal to the character at index k-n in the argument str
.
str
- a string.public StringBuilder append(StringBuffer sb)
Appends the specified StringBuffer
to this sequence.
The characters of the StringBuffer
argument are appended, in order, to this sequence, increasing the length of this sequence by the length of the argument. If sb
is null
, then the four characters "null"
are appended to this sequence.
Let n be the length of this character sequence just prior to execution of the append
method. Then the character at index k in the new character sequence is equal to the character at index k in the old character sequence, if k is less than n; otherwise, it is equal to the character at index k-n in the argument sb
.
sb
- the StringBuffer
to append.public StringBuilder append(CharSequence s)
Description copied from interface: Appendable
Appends the specified character sequence to this Appendable
.
Depending on which class implements the character sequence csq
, the entire sequence may not be appended. For instance, if csq
is a CharBuffer
then the subsequence to append is defined by the buffer's position and limit.
append
in interface Appendable
s
- The character sequence to append. If csq
is null
, then the four characters "null"
are appended to this Appendable.Appendable
public StringBuilder append(CharSequence s, int start, int end)
Appends a subsequence of the specified CharSequence
to this sequence.
Characters of the argument s
, starting at index start
, are appended, in order, to the contents of this sequence up to the (exclusive) index end
. The length of this sequence is increased by the value of end - start
.
Let n be the length of this character sequence just prior to execution of the append
method. Then the character at index k in this character sequence becomes equal to the character at index k in this sequence, if k is less than n; otherwise, it is equal to the character at index k+start-n in the argument s
.
If s
is null
, then this method appends characters as if the s parameter was a sequence containing the four characters "null"
.
append
in interface Appendable
s
- the sequence to append.start
- the starting index of the subsequence to be appended.end
- the end index of the subsequence to be appended.IndexOutOfBoundsException
- if start
is negative, or start
is greater than end
or end
is greater than s.length()
public StringBuilder append(char[] str)
Appends the string representation of the char
array argument 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 exactly as if the argument were converted to a string by the method String.valueOf(char[])
, and the characters of that string were then appended
to this character sequence.
str
- the characters to be appended.public StringBuilder append(char[] str, int offset, int len)
Appends the string representation of a subarray of the char
array argument to this sequence.
Characters of the char
array str
, starting at index offset
, are appended, in order, to the contents of this sequence. The length of this sequence increases by the value of len
.
The overall effect is exactly as if the arguments were converted to a string by the method String.valueOf(char[],int,int)
, and the characters of that string were then appended
to this character sequence.
str
- the characters to be appended.offset
- the index of the first char
to append.len
- the number of char
s to append.IndexOutOfBoundsException
- if offset < 0
or len < 0
or offset+len > str.length
public StringBuilder append(boolean b)
Appends the string representation of the boolean
argument to the sequence.
The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(boolean)
, and the characters of that string were then appended
to this character sequence.
b
- a boolean
.public StringBuilder append(char c)
Appends the string representation of the char
argument to this sequence.
The argument is appended to the contents of this sequence. The length of this sequence increases by 1
.
The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(char)
, and the character in that string were then appended
to this character sequence.
append
in interface Appendable
c
- a char
.public StringBuilder append(int i)
Appends the string representation of the int
argument to this sequence.
The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(int)
, and the characters of that string were then appended
to this character sequence.
i
- an int
.public StringBuilder append(long lng)
Appends the string representation of the long
argument to this sequence.
The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(long)
, and the characters of that string were then appended
to this character sequence.
lng
- a long
.public StringBuilder append(float f)
Appends the string representation of the float
argument to this sequence.
The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(float)
, and the characters of that string were then appended
to this character sequence.
f
- a float
.public StringBuilder append(double d)
Appends the string representation of the double
argument to this sequence.
The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(double)
, and the characters of that string were then appended
to this character sequence.
d
- a double
.public StringBuilder appendCodePoint(int codePoint)
Appends the string representation of the codePoint
argument to this sequence.
The argument is appended to the contents of this sequence. The length of this sequence increases by Character.charCount(codePoint)
.
The overall effect is exactly as if the argument were converted to a char
array by the method Character.toChars(int)
and the character in that array were then appended
to this character sequence.
codePoint
- a Unicode code pointpublic StringBuilder delete(int start, int end)
Removes the characters in a substring of this sequence. The substring begins at the specified start
and extends to the character at index end - 1
or to the end of the sequence if no such character exists. If start
is equal to end
, no changes are made.
start
- The beginning index, inclusive.end
- The ending index, exclusive.StringIndexOutOfBoundsException
- if start
is negative, greater than length()
, or greater than end
.public StringBuilder deleteCharAt(int index)
Removes the char
at the specified position in this sequence. This sequence is shortened by one char
.
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 char
s to remove by calling Character.charCount(thisSequence.codePointAt(index))
, where thisSequence
is this sequence.
index
- Index of char
to removeStringIndexOutOfBoundsException
- if the index
is negative or greater than or equal to length()
.public StringBuilder replace(int start, int end, String str)
Replaces the characters in a substring of this sequence with characters in the specified String
. The substring begins at the specified start
and extends to the character at index 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 String
is inserted at start
. (This sequence will be lengthened to accommodate the specified String if necessary.)
start
- The beginning index, inclusive.end
- The ending index, exclusive.str
- String that will replace previous contents.StringIndexOutOfBoundsException
- if start
is negative, greater than length()
, or greater than end
.public StringBuilder insert(int index, char[] str, int offset, int len)
Inserts the string representation of a subarray of the str
array argument into this sequence. The subarray begins at the specified offset
and extends len
char
s. The characters of the subarray are inserted into this sequence at the position indicated by index
. The length of this sequence increases by len
char
s.
index
- position at which to insert subarray.str
- A char
array.offset
- the index of the first char
in subarray to be inserted.len
- the number of char
s in the subarray to be inserted.StringIndexOutOfBoundsException
- if index
is negative or greater than length()
, or offset
or len
are negative, or (offset+len)
is greater than str.length
.public StringBuilder insert(int offset, Object obj)
Inserts the string representation of the Object
argument into this character sequence.
The overall effect is exactly as if the second argument were converted to a string by the method String.valueOf(Object)
, and the characters of that string were then inserted
into this character sequence at the indicated offset.
The offset
argument must be greater than or equal to 0
, and less than or equal to the length of this sequence.
offset
- the offset.obj
- an Object
.StringIndexOutOfBoundsException
- if the offset is invalid.public StringBuilder insert(int offset, String str)
Inserts the string into this character sequence.
The characters of the 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 str
is null
, then the four characters "null"
are inserted into this sequence.
The character at index k in the new character sequence is equal to:
offset
-offset
in the argument str
, if k is not less than offset
but is less than offset+str.length()
-str.length()
in the old character sequence, if k is not less than offset+str.length()
The offset
argument must be greater than or equal to 0
, and less than or equal to the length of this sequence.
offset
- the offset.str
- a string.StringIndexOutOfBoundsException
- if the offset is invalid.public StringBuilder insert(int offset, char[] str)
Inserts the string representation of the char
array argument into this sequence.
The characters of the array argument are inserted into the contents of this sequence at the position indicated by offset
. The length of this sequence increases by the length of the argument.
The overall effect is exactly as if the second argument were converted to a string by the method String.valueOf(char[])
, and the characters of that string were then inserted
into this character sequence at the indicated offset.
The offset
argument must be greater than or equal to 0
, and less than or equal to the length of this sequence.
offset
- the offset.str
- a character array.StringIndexOutOfBoundsException
- if the offset is invalid.public StringBuilder insert(int dstOffset, CharSequence s)
Inserts the specified CharSequence
into this sequence.
The characters of the 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.
The result of this method is exactly the same as if it were an invocation of this object's insert
(dstOffset, s, 0, s.length()) method.
If s
is null
, then the four characters "null"
are inserted into this sequence.
dstOffset
- the offset.s
- the sequence to be insertedIndexOutOfBoundsException
- if the offset is invalid.public StringBuilder insert(int dstOffset, CharSequence s, int start, int end)
Inserts a subsequence of the specified CharSequence
into this sequence.
The subsequence of the argument s
specified by start
and 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 end - start
.
The character at index k in this sequence becomes equal to:
dstOffset
+start-dstOffset
in the argument s
, if k is greater than or equal to dstOffset
but is less than dstOffset+end-start
-(end-start)
in this sequence, if k is greater than or equal to dstOffset+end-start
The dstOffset
argument must be greater than or equal to 0
, and less than or equal to the length of this sequence.
The start argument must be nonnegative, and not greater than end
.
The end argument must be greater than or equal to start
, and less than or equal to the length of s.
If s
is null
, then this method inserts characters as if the s parameter was a sequence containing the four characters "null"
.
dstOffset
- the offset in this sequence.s
- the sequence to be inserted.start
- the starting index of the subsequence to be inserted.end
- the end index of the subsequence to be inserted.IndexOutOfBoundsException
- if dstOffset
is negative or greater than this.length()
, or start
or end
are negative, or start
is greater than end
or end
is greater than s.length()
public StringBuilder insert(int offset, boolean b)
Inserts the string representation of the boolean
argument into this sequence.
The overall effect is exactly as if the second argument were converted to a string by the method String.valueOf(boolean)
, and the characters of that string were then inserted
into this character sequence at the indicated offset.
The offset
argument must be greater than or equal to 0
, and less than or equal to the length of this sequence.
offset
- the offset.b
- a boolean
.StringIndexOutOfBoundsException
- if the offset is invalid.public StringBuilder insert(int offset, char c)
Inserts the string representation of the char
argument into this sequence.
The overall effect is exactly as if the second argument were converted to a string by the method String.valueOf(char)
, and the character in that string were then inserted
into this character sequence at the indicated offset.
The offset
argument must be greater than or equal to 0
, and less than or equal to the length of this sequence.
offset
- the offset.c
- a char
.IndexOutOfBoundsException
- if the offset is invalid.public StringBuilder insert(int offset, int i)
Inserts the string representation of the second int
argument into this sequence.
The overall effect is exactly as if the second argument were converted to a string by the method String.valueOf(int)
, and the characters of that string were then inserted
into this character sequence at the indicated offset.
The offset
argument must be greater than or equal to 0
, and less than or equal to the length of this sequence.
offset
- the offset.i
- an int
.StringIndexOutOfBoundsException
- if the offset is invalid.public StringBuilder insert(int offset, long l)
Inserts the string representation of the long
argument into this sequence.
The overall effect is exactly as if the second argument were converted to a string by the method String.valueOf(long)
, and the characters of that string were then inserted
into this character sequence at the indicated offset.
The offset
argument must be greater than or equal to 0
, and less than or equal to the length of this sequence.
offset
- the offset.l
- a long
.StringIndexOutOfBoundsException
- if the offset is invalid.public StringBuilder insert(int offset, float f)
Inserts the string representation of the float
argument into this sequence.
The overall effect is exactly as if the second argument were converted to a string by the method String.valueOf(float)
, and the characters of that string were then inserted
into this character sequence at the indicated offset.
The offset
argument must be greater than or equal to 0
, and less than or equal to the length of this sequence.
offset
- the offset.f
- a float
.StringIndexOutOfBoundsException
- if the offset is invalid.public StringBuilder insert(int offset, double d)
Inserts the string representation of the double
argument into this sequence.
The overall effect is exactly as if the second argument were converted to a string by the method String.valueOf(double)
, and the characters of that string were then inserted
into this character sequence at the indicated offset.
The offset
argument must be greater than or equal to 0
, and less than or equal to the length of this sequence.
offset
- the offset.d
- a double
.StringIndexOutOfBoundsException
- if the offset is invalid.public int indexOf(String str)
Returns the index within this string of the first occurrence of the specified substring. The integer returned is the smallest value k such that:
this.toString().startsWith(str, <i>k</i>)is
true
. str
- any string.-1
is returned.public int indexOf(String str, int fromIndex)
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 k
for which:
k >= Math.min(fromIndex, this.length()) && this.toString().startsWith(str, k)If no such value of k exists, then -1 is returned.
str
- the substring for which to search.fromIndex
- the index from which to start the search.public int lastIndexOf(String str)
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 this.length()
. The returned index is the largest value k such that
this.toString().startsWith(str, k)is true.
str
- the substring to search for.-1
is returned.public int lastIndexOf(String str, int fromIndex)
Returns the index within this string of the last occurrence of the specified substring. The integer returned is the largest value k such that:
k <= Math.min(fromIndex, this.length()) && this.toString().startsWith(str, k)If no such value of k exists, then -1 is returned.
str
- the substring to search for.fromIndex
- the index to start the search from.public StringBuilder reverse()
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 n be the character length of this character sequence (not the length in char
values) just prior to execution of the reverse
method. Then the character at index k in the new character sequence is equal to the character at index n-k-1 in the old character sequence.
Note that the reverse operation may result in producing surrogate pairs that were unpaired low-surrogates and high-surrogates before the operation. For example, reversing "\uDC00\uD800" produces "\uD800\uDC00" which is a valid surrogate pair.
public String toString()
Returns a string representing the data in this sequence. A new String
object is allocated and initialized to contain the character sequence currently represented by this object. This String
is then returned. Subsequent changes to this sequence do not affect the contents of the String
.
toString
in interface CharSequence
public int length()
Returns the length (character count).
length
in interface CharSequence
public int capacity()
Returns the current capacity. The capacity is the amount of storage available for newly inserted characters, beyond which an allocation will occur.
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, then a new internal array is allocated with greater capacity. The new capacity is the larger of:
minimumCapacity
argument. 2
. minimumCapacity
argument is nonpositive, this method takes no action and simply returns. Note that subsequent operations on this object can reduce the actual capacity below that requested here. minimumCapacity
- the minimum desired capacity.public void trimToSize()
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 capacity()
method.
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 nonnegative index k less than newLength
, the character at index k in the new character sequence is the same as the character at index k in the old sequence if k is less than the length of the old character sequence; otherwise, it is the null character '\u0000'
. In other words, if the newLength
argument is less than the current length, the length is changed to the specified length.
If the newLength
argument is greater than or equal to the current length, sufficient null characters ('\u0000'
) are appended so that length becomes the newLength
argument.
The newLength
argument must be greater than or equal to 0
.
newLength
- the new lengthIndexOutOfBoundsException
- if the newLength
argument is negative.public char charAt(int index)
Returns the char
value in this sequence at the specified index. The first char
value is at index 0
, the next at index 1
, and so on, as in array indexing.
The index argument must be greater than or equal to 0
, and less than the length of this sequence.
If the char
value specified by the index is a surrogate, the surrogate value is returned.
charAt
in interface CharSequence
index
- the index of the desired char
value.char
value at the specified index.IndexOutOfBoundsException
- if index
is negative or greater than or equal to length()
.public int codePointAt(int index)
Returns the character (Unicode code point) at the specified index. The index refers to char
values (Unicode code units) and ranges from 0
to length()
- 1
.
If the char
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 char
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 char
value at the given index is returned.
index
- the index to the char
valuesindex
IndexOutOfBoundsException
- if the index
argument is negative or not less than the length of this sequence.public int codePointBefore(int index)
Returns the character (Unicode code point) before the specified index. The index refers to char
values (Unicode code units) and ranges from 1
to length()
.
If the char
value at (index - 1)
is in the low-surrogate range, (index - 2)
is not negative, and the char
value at (index -
2)
is in the high-surrogate range, then the supplementary code point value of the surrogate pair is returned. If the char
value at index -
1
is an unpaired low-surrogate or a high-surrogate, the surrogate value is returned.
index
- the index following the code point that should be returnedIndexOutOfBoundsException
- if the index
argument is less than 1 or greater than the length of this sequence.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 begins at the specified beginIndex
and extends to the char
at index endIndex - 1
. Thus the length (in char
s) of the text range is endIndex-beginIndex
. Unpaired surrogates within this sequence count as one code point each.
beginIndex
- the index to the first char
of the text range.endIndex
- the index after the last char
of the text range.IndexOutOfBoundsException
- if the beginIndex
is negative, or endIndex
is larger than the length of this sequence, or beginIndex
is larger than endIndex
.public int offsetByCodePoints(int index, int codePointOffset)
Returns the index within this sequence that is offset from the given index
by codePointOffset
code points. Unpaired surrogates within the text range given by index
and codePointOffset
count as one code point each.
index
- the index to be offsetcodePointOffset
- the offset in code pointsIndexOutOfBoundsException
- if index
is negative or larger then the length of this sequence, or if codePointOffset
is positive and the subsequence starting with index
has fewer than codePointOffset
code points, or if codePointOffset
is negative and the subsequence before index
has fewer than the absolute value of codePointOffset
code points.public void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
Characters are copied from this sequence into the destination character array dst
. The first character to be copied is at index srcBegin
; the last character to be copied is at index srcEnd-1
. The total number of characters to be copied is srcEnd-srcBegin
. The characters are copied into the subarray of dst
starting at index dstBegin
and ending at index:
dstbegin + (srcEnd-srcBegin) - 1
srcBegin
- start copying at this offset.srcEnd
- stop copying at this offset.dst
- the array to copy the data into.dstBegin
- offset into dst
.IndexOutOfBoundsException
- if any of the following is true: srcBegin
is negative dstBegin
is negative srcBegin
argument is greater than the srcEnd
argument. srcEnd
is greater than this.length()
. dstBegin+srcEnd-srcBegin
is greater than dst.length
public void setCharAt(int index, char ch)
The character at the specified index is set to ch
. This sequence is altered to represent a new character sequence that is identical to the old character sequence, except that it contains the character ch
at position index
.
The index argument must be greater than or equal to 0
, and less than the length of this sequence.
index
- the index of the character to modify.ch
- the new character.IndexOutOfBoundsException
- if index
is negative or greater than or equal to length()
.public String substring(int start)
Returns a new 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.
start
- The beginning index, inclusive.StringIndexOutOfBoundsException
- if start
is less than zero, or greater than the length of this object.public CharSequence subSequence(int start, int end)
Returns a new character sequence that is a subsequence of this sequence.
An invocation of this method of the form
sb.subSequence(begin, end)behaves in exactly the same way as the invocation
sb.substring(begin, end)This method is provided so that this class can implement the
CharSequence
interface.subSequence
in interface CharSequence
start
- the start index, inclusive.end
- the end index, exclusive.IndexOutOfBoundsException
- if start
or end
are negative, if end
is greater than length()
, or if start
is greater than end
public String substring(int start, int end)
Returns a new String
that contains a subsequence of characters currently contained in this sequence. The substring begins at the specified start
and extends to the character at index end - 1
.
start
- The beginning index, inclusive.end
- The ending index, exclusive.StringIndexOutOfBoundsException
- if start
or end
are negative or greater than length()
, or start
is greater than end
.
© 1993–2017, Oracle and/or its affiliates. All rights reserved.
Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.