java.lang.StringBufferString buffers are safe for use by multiple threads. The methods are synchronized where necessary so that all the operations on any particular instance behave as if they occur in some serial order that is consistent with the order of the method calls made by each of the individual threads involved.
The principal operations on a StringBuffer 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 buffer. The
append method always adds these characters at the end
of the buffer; the insert method adds the characters at
a specified point.
For example, if z refers to a string buffer object
whose current contents are "start", then
the method call z.append("le") would cause the string
buffer to contain "startle", whereas
z.insert(4, "le") would alter the string buffer to
contain "starlet".
In general, if sb refers to an instance of a StringBuffer,
then sb.append(x) has the same effect as
sb.insert(sb.length(), x).
Whenever an operation occurs involving a source sequence (such as appending or inserting from a source sequence) this class synchronizes only on the string buffer performing the operation, not on the source.
Every string buffer has a capacity. As long as the length of the character sequence contained in the string buffer does not exceed the capacity, it is not necessary to allocate a new internal buffer array. If the internal buffer overflows, it is automatically made larger. As of release JDK 5, this class has been supplemented with an equivalent class designed for use by a single thread, StringBuilder. The StringBuilder class should generally be used in preference to this one, as it supports all of the same operations but it is faster, as it performs no synchronization.
| Constructor Summary | ||
| StringBuffer() Constructs a string buffer with no characters in it and an
initial capacity of 16 characters. |
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| StringBuffer(int capacity) Constructs a string buffer with no characters in it and
the specified initial capacity. |
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| StringBuffer(CharSequence seq) Constructs a string buffer that contains the same characters
as the specified CharSequence. |
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| StringBuffer(String str) Constructs a string buffer initialized to the contents of the
specified string. |
| Method Summary | ||
| append(boolean b) Appends the string representation of the boolean
argument to the sequence. |
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| append(char c) Appends the specified character to this Appendable. |
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| append(char[] str) Appends the string representation of the char array
argument to this sequence. |
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| append(char[] str, int offset, int len) Appends the string representation of a subarray of the
char array argument to this sequence. |
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| append(double d) Appends the string representation of the double
argument to this sequence. |
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| append(float f) Appends the string representation of the float
argument to this sequence. |
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| append(int i) Appends the string representation of the int
argument to this sequence. |
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| append(CharSequence s) Appends the specified CharSequence to this
sequence. |
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| append(CharSequence s, int start, int end) Appends a subsequence of the specified character sequence to this
Appendable. |
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| append(Object obj) Appends the string representation of the Object
argument. |
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| append(String str) Appends the specified string to this character sequence. |
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| append(StringBuffer sb) Appends the specified StringBuffer to this sequence. |
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| append(long lng) Appends the string representation of the long
argument to this sequence. |
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| appendCodePoint(int codePoint) Appends the string representation of the codePoint
argument to this sequence. |
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int |
capacity() Returns the current capacity. |
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char |
charAt(int index) Returns the char value at the specified index. |
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int |
codePointAt(int index) Returns the character (Unicode code point) at the specified
index. |
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int |
codePointBefore(int index) Returns the character (Unicode code point) before the specified
index. |
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int |
codePointCount(int beginIndex, int endIndex) Returns the number of Unicode code points in the specified text
range of this sequence. |
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| delete(int start, int end) Removes the characters in a substring of this sequence. |
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| deleteCharAt(int index) Removes the char at the specified position in this
sequence. |
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void |
ensureCapacity(int minimumCapacity) Ensures that the capacity is at least equal to the specified minimum. |
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void |
getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) Characters are copied from this sequence into the
destination character array dst. |
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int |
indexOf(String str) Returns the index within this string of the first occurrence of the
specified substring. |
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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. |
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| insert(int offset, boolean b) Inserts the string representation of the boolean
argument into this sequence. |
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| insert(int offset, char c) Inserts the string representation of the char
argument into this sequence. |
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| insert(int offset, char[] str) Inserts the string representation of the char array
argument into this sequence. |
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| insert(int index, char[] str, int offset, int len) Inserts the string representation of a subarray of the str
array argument into this sequence. |
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| insert(int offset, double d) Inserts the string representation of the double
argument into this sequence. |
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| insert(int offset, float f) Inserts the string representation of the float
argument into this sequence. |
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| insert(int offset, int i) Inserts the string representation of the second int
argument into this sequence. |
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| insert(int dstOffset, CharSequence s) Inserts the specified CharSequence into this sequence. |
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| insert(int dstOffset, CharSequence s, int start, int end) Inserts a subsequence of the specified CharSequence into
this sequence. |
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| insert(int offset, Object obj) Inserts the string representation of the Object
argument into this character sequence. |
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| insert(int offset, String str) Inserts the string into this character sequence. |
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| insert(int offset, long l) Inserts the string representation of the long
argument into this sequence. |
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int |
lastIndexOf(String str) Returns the index within this string of the rightmost occurrence
of the specified substring. |
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int |
lastIndexOf(String str, int fromIndex) Returns the index within this string of the last occurrence of the
specified substring. |
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int |
length() Returns the length of this character sequence. |
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int |
offsetByCodePoints(int index, int codePointOffset) Returns the index within this sequence that is offset from the
given index by codePointOffset code
points. |
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| replace(int start, int end, String str) Replaces the characters in a substring of this sequence
with characters in the specified String. |
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| reverse() Causes this character sequence to be replaced by the reverse of
the sequence. |
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void |
setCharAt(int index, char ch) The character at the specified index is set to ch. |
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void |
setLength(int newLength) Sets the length of the character sequence. |
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| subSequence(int start, int end) Returns a new CharSequence that is a subsequence of this sequence. |
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| substring(int start) Returns a new String that contains a subsequence of
characters currently contained in this character sequence. |
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| substring(int start, int end) Returns a new String that contains a subsequence of
characters currently contained in this sequence. |
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| toString() Returns a string containing the characters in this sequence in the same
order as this sequence. |
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void |
trimToSize() Attempts to reduce storage used for the character sequence. |
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| Methods inherited from class java.lang.Object |
| clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
16 plus the length of the string argument.CharSequence. The initial capacity of
the string buffer is 16 plus the length of the
CharSequence argument.
If the length of the specified CharSequence is
less than or equal to zero, then an empty buffer of capacity
16 is returned.
chars in the sequence.chars in this sequenceminimumCapacity argument.
2.
minimumCapacity argument is nonpositive, this
method takes no action and simply returns.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 argument is negative.char value at the specified index. An index ranges from zero
to length() - 1. The first char value of the sequence is at
index zero, the next at index one, and so on, as for array
indexing.
If the char value specified by the index is a
surrogate, the surrogate
value is returned.
char value to be returnedchar valuechar values
(Unicode code units) and ranges from 0 to
java.lang.AbstractStringBuilder.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.
char valuesindexchar values
(Unicode code units) and ranges from 1 to java.lang.AbstractStringBuilder.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.
beginIndex and extends to the char at
index endIndex - 1. Thus the length (in
chars) of the text range is
endIndex-beginIndex. Unpaired surrogates within
this sequence count as one code point each.char of
the text range.char of
the text range.index by codePointOffset code
points. Unpaired surrogates within the text range given by
index and codePointOffset count as
one code point each.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
dst.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
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.
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.
Object.
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.
The characters of the StringBuffer argument are appended, in order, to the contents of this StringBuffer, increasing the length of this StringBuffer by the length of the argument. If sb is null, then the four characters "null" are appended to this StringBuffer.
Let n be the length of the old character sequence, the one
contained in the StringBuffer 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.
This method synchronizes on this (the destination)
object but does not synchronize on the source (sb).
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());
This method synchronizes on this (the destination)
object but does not synchronize on the source (s).
If s is null, then the four characters
"null" are appended.
CharSequence to append.An invocation of this method of the form out.append(csq, start, end) when csq is not null, behaves in exactly the same way as the invocation
out.append(csq.subSequence(start, end)) 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.
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.
char to append.chars to append.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.
boolean.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.
int.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.
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.
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.
float.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.
double.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.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 chars to remove by calling
Character.charCount(thisSequence.codePointAt(index)),
where thisSequence is this sequence.
char to removeString. 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.)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 is
less than zero, or greater than the length of this object.CharSequence that is a subsequence of this sequence.
The subsequence starts with the char value at the specified index and
ends with the char value at index end - 1. The length
(in chars) of the
returned sequence is end - start, so if start == end
then an empty sequence is returned. 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
or end are negative or greater than
length(), or start is
greater than end.str
array argument into this sequence. The subarray begins at the
specified offset and extends len chars.
The characters of the subarray are inserted into this sequence at
the position indicated by index. The length of this
sequence increases by len chars.char array.char in subarray to
be inserted.chars in the subarray to
be inserted.index
is negative or greater than length(), or
offset or len are negative, or
(offset+len) is greater than
str.length.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.
Object.
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.
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.
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.
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
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()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.
boolean.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.
char.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.
int.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.
long.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.
float.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.
double.isthis.toString().startsWith(str, k)
true.-1 is returned.
k >= Math.min(fromIndex, str.length()) &&
this.toString().startsWith(str, k)
If no such value of k exists, then -1 is returned.this.length().
The returned index is the largest value k such that
is true.this.toString().startsWith(str, k)
-1 is returned.
k <= Math.min(fromIndex, str.length()) &&
this.toString().startsWith(str, k)
If no such value of k exists, then -1 is returned.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.