java.lang.Object java.lang.StringBuilder
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.
StringBuffer
,
String
,
Serialized FormConstructor Summary | |
---|---|
StringBuilder()
Constructs a string builder with no characters in it and an initial capacity of 16 characters. |
|
StringBuilder(CharSequence seq)
Constructs a string builder that contains the same characters as the specified CharSequence . |
|
StringBuilder(int capacity)
Constructs a string builder with no characters in it and an initial capacity specified by the capacity argument. |
|
StringBuilder(String str)
Constructs a string builder initialized to the contents of the specified string. |
Method Summary | |
---|---|
StringBuilder |
append(boolean b)
Appends the string representation of the boolean
argument to the sequence. |
StringBuilder |
append(char c)
Appends the string representation of the char
argument to this sequence. |
StringBuilder |
append(char[] str)
Appends the string representation of the char array
argument to this sequence. |
StringBuilder |
append(char[] str,
int offset,
int len)
Appends the string representation of a subarray of the char array argument to this sequence. |
StringBuilder |
append(CharSequence s)
Appends the specified CharSequence to this
sequence. |
StringBuilder |
append(CharSequence s,
int srcOffset,
int len)
Appends a subsequence of the specified CharSequence to this
sequence. |
StringBuilder |
append(double d)
Appends the string representation of the double
argument to this sequence. |
StringBuilder |
append(float f)
Appends the string representation of the float
argument to this sequence. |
StringBuilder |
append(int i)
Appends the string representation of the int
argument to this sequence. |
StringBuilder |
append(long lng)
Appends the string representation of the long
argument to this sequence. |
StringBuilder |
append(Object obj)
Appends the string representation of the Object
argument. |
StringBuilder |
append(String str)
Appends the specified string to this character sequence. |
StringBuilder |
append(StringBuffer sb)
Appends the specified StringBuffer to this sequence. |
StringBuilder |
appendCodePoint(int codePoint)
Appends the string representation of the codePoint
argument to this sequence. |
int |
capacity()
Returns the current capacity. |
char |
charAt(int index)
Returns the char value in this sequence at the specified index. |
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. |
StringBuilder |
delete(int start,
int end)
Removes the characters in a substring of this sequence. |
StringBuilder |
deleteCharAt(int index)
Removes the character at the specified position in this sequence. |
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)
Characters are copied from this sequence into the destination character array dst . |
int |
indexOf(String str)
Returns the index within this string of the first occurrence of the specified substring. |
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. |
StringBuilder |
insert(int offset,
boolean b)
Inserts the string representation of the boolean
argument into this sequence. |
StringBuilder |
insert(int offset,
char c)
Inserts the string representation of the char
argument into this sequence. |
StringBuilder |
insert(int offset,
char[] str)
Inserts the string representation of the char array
argument into this sequence. |
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. |
StringBuilder |
insert(int dstOffset,
CharSequence s)
Inserts the specified CharSequence into this sequence. |
StringBuilder |
insert(int dstOffset,
CharSequence s,
int srcOffset,
int len)
Inserts a subsequence of the specified CharSequence into
this sequence. |
StringBuilder |
insert(int offset,
double d)
Inserts the string representation of the double
argument into this sequence. |
StringBuilder |
insert(int offset,
float f)
Inserts the string representation of the float
argument into this sequence. |
StringBuilder |
insert(int offset,
int i)
Inserts the string representation of the second int
argument into this sequence. |
StringBuilder |
insert(int offset,
long l)
Inserts the string representation of the long
argument into this sequence. |
StringBuilder |
insert(int offset,
Object obj)
Inserts the string representation of the Object
argument 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 this string of the rightmost occurrence of the specified substring. |
int |
lastIndexOf(String str,
int fromIndex)
Returns the index within this string of the last occurrence of the specified substring. |
int |
length()
Returns the length (character count). |
StringBuilder |
replace(int start,
int end,
String str)
Replaces the characters in a substring of this sequence with characters in the specified String . |
StringBuilder |
reverse()
Causes this character sequence to be replaced by the reverse 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 that contains a subsequence of
characters currently contained in this character sequence. |
String |
substring(int start,
int end)
Returns a new String that contains a subsequence of
characters currently contained in this sequence. |
String |
toString()
Returns a string representing the data in this sequence. |
void |
trimToSize()
Attempts to reduce storage used for the character sequence. |
Methods inherited from class java.lang.Object |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Methods inherited from interface java.lang.CharSequence |
---|
charAt, length, subSequence |
Constructor Detail |
---|
public StringBuilder()
public StringBuilder(int capacity)
capacity
argument.
capacity
- the initial capacity.
NegativeArraySizeException
- if the capacity
argument is less than 0
.public StringBuilder(String str)
16
plus the length of the string argument.
str
- the initial contents of the buffer.
NullPointerException
- if str
is null
public StringBuilder(CharSequence seq)
CharSequence
. The initial capacity of
the string builder is 16
plus the length of the
CharSequence
argument.
seq
- the sequence to copy.
NullPointerException
- if seq
is null
Method Detail |
---|
public StringBuilder append(Object obj)
Object
argument.
The argument is converted to a string as if by the method
String.valueOf
, and the characters of that
string are then appended to this sequence.
obj
- an Object
.
String.valueOf(java.lang.Object)
,
append(java.lang.String)
public StringBuilder append(String str)
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)
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)
CharSequence
to this
sequence.
The characters of the CharSequence
argument are appended,
in order, increasing the length of this sequence by the length of the
argument.
The result of this method is exactly the same as if it were an
invocation of this.append(s, 0, s.length());
If s
is null
, then the four characters
"null"
are appended.
append
in interface Appendable
s
- the CharSequence
to append.
public StringBuilder append(CharSequence s, int srcOffset, int len)
CharSequence
to this
sequence.
Characters of the CharSequence
argument, starting at
index srcOffset
, are appended, in order, to the contents of
this sequence. The length of this sequence is increased by the value of
len
.
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 s, if k is less than n;
otherwise, it is equal to the character at index k+srcOffset-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"
.
s
- the CharSequence
to append.srcOffset
- the index of the first character in s to be
appended.len
- the number of characters in s to be appended.
public StringBuilder append(char[] str)
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)
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.
public StringBuilder append(boolean b)
boolean
argument to the sequence.
The argument is converted to a string as if by the method
String.valueOf
, and the characters of that
string are then appended to this sequence.
b
- a boolean
.
String.valueOf(boolean)
,
append(java.lang.String)
public StringBuilder append(char c)
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)
int
argument to this sequence.
The argument is converted to a string as if by the method
String.valueOf
, and the characters of that
string are then appended to this sequence.
i
- an int
.
String.valueOf(int)
,
append(java.lang.String)
public StringBuilder append(long lng)
long
argument to this sequence.
The argument is converted to a string as if by the method
String.valueOf
, and the characters of that
string are then appended to this sequence.
lng
- a long
.
String.valueOf(long)
,
append(java.lang.String)
public StringBuilder append(float f)
float
argument to this sequence.
The argument is converted to a string as if by the method
String.valueOf
, and the characters of that
string are then appended to this string sequence.
f
- a float
.
String.valueOf(float)
,
append(java.lang.String)
public StringBuilder append(double d)
double
argument to this sequence.
The argument is converted to a string as if by the method
String.valueOf
, and the characters of that
string are then appended to this sequence.
d
- a double
.
String.valueOf(double)
,
append(java.lang.String)
public StringBuilder appendCodePoint(int codePoint)
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 point
public StringBuilder delete(int start, int end)
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.
public StringBuilder deleteCharAt(int index)
index
- Index of character to remove
public StringBuilder replace(int start, int end, String str)
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.
public StringBuilder insert(int index, char[] str, int offset, int len)
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.
public StringBuilder insert(int offset, Object obj)
Object
argument into this character sequence.
The second argument is converted to a string as if by the method
String.valueOf
, and the characters of that
string are then inserted into this 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
.
String.valueOf(java.lang.Object)
,
insert(int, java.lang.String)
,
length()
public StringBuilder insert(int offset, String str)
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.
length()
public StringBuilder insert(int offset, char[] str)
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 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 position indicated by
offset
.
offset
- the offset.str
- a character array.
public StringBuilder insert(int dstOffset, CharSequence s)
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 inserted
public StringBuilder insert(int dstOffset, CharSequence s, int srcOffset, int len)
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 character at index k in this sequence becomes equal to:
dstOffset
+srcOffset-dstOffset
in
the argument s
, if k is not less than
dstOffset
but is less than dstOffset+len
-len
in this sequence,
if k is not less than dstOffset+len
The dstOffset argument must be greater than or equal to
0
, and less than or equal to the length of this
sequence.
The srcOffset argument must be greater than or equal to
0
, 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.srcOffset
- the index of the first character in s to be
inserted.len
- the number of characters in s to be inserted.
public StringBuilder insert(int offset, boolean b)
boolean
argument into this sequence.
The second argument is converted to a string as if by the method
String.valueOf
, and the characters of that
string are then inserted into this 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
.
String.valueOf(boolean)
,
insert(int, java.lang.String)
,
length()
public StringBuilder insert(int offset, char c)
char
argument into this sequence.
The second argument is inserted into the contents of this sequence
at the position indicated by offset
. The length
of this sequence increases by one.
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 inserted
into
this character sequence at the position indicated by
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
.
length()
public StringBuilder insert(int offset, int i)
int
argument into this sequence.
The second argument is converted to a string as if by the method
String.valueOf
, and the characters of that
string are then inserted into this 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
.
String.valueOf(int)
,
insert(int, java.lang.String)
,
length()
public StringBuilder insert(int offset, long l)
long
argument into this sequence.
The second argument is converted to a string as if by the method
String.valueOf
, and the characters of that
string are then inserted into this sequence at the position
indicated by 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
.
String.valueOf(long)
,
insert(int, java.lang.String)
,
length()
public StringBuilder insert(int offset, float f)
float
argument into this sequence.
The second argument is converted to a string as if by the method
String.valueOf
, and the characters of that
string are then inserted into this 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
.
String.valueOf(float)
,
insert(int, java.lang.String)
,
length()
public StringBuilder insert(int offset, double d)
double
argument into this sequence.
The second argument is converted to a string as if by the method
String.valueOf
, and the characters of that
string are then inserted into this 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
.
String.valueOf(double)
,
insert(int, java.lang.String)
,
length()
public int indexOf(String str)
isthis.toString().startsWith(str, k)
true
.
str
- any string.
-1
is returned.public int indexOf(String str, int fromIndex)
If no such value of k exists, then -1 is returned.k >= Math.min(fromIndex, str.length()) && this.toString().startsWith(str, k)
str
- the substring for which to search.fromIndex
- the index from which to start the search.
public int lastIndexOf(String str)
this.length()
.
The returned index is the largest value k such that
is true.this.toString().startsWith(str, k)
str
- the substring to search for.
-1
is returned.public int lastIndexOf(String str, int fromIndex)
If no such value of k exists, then -1 is returned.k <= Math.min(fromIndex, str.length()) && this.toString().startsWith(str, k)
str
- the substring to search for.fromIndex
- the index to start the search from.
public StringBuilder reverse()
char
values) just prior to
execution of the reverse
method. Then the
characrer 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()
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()
length
in interface CharSequence
public int capacity()
public void ensureCapacity(int minimumCapacity)
minimumCapacity
argument.
2
.
minimumCapacity
argument is nonpositive, this
method takes no action and simply returns.
minimumCapacity
- the minimum desired capacity.public void trimToSize()
capacity()
method.
public void setLength(int newLength)
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 length
IndexOutOfBoundsException
- if the
newLength
argument is negative.public char charAt(int index)
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)
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
values
index
IndexOutOfBoundsException
- if the index
argument is negative or not less than the length of this
sequence.public int codePointBefore(int index)
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 returned
IndexOutOfBoundsException
- if the index
argument is less than 1 or greater than the length
of this sequence.public void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
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
.
NullPointerException
- if dst
is
null
.
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)
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)
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)
An invocation of this method of the form
behaves in exactly the same way as the invocationsb.subSequence(begin, end)
This method is provided so that this class can implement thesb.substring(begin, end)
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 endpublic String substring(int start, int end)
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
.