StringBuffer
public
final
class
StringBuffer
extends Object
implements
Appendable,
CharSequence,
Serializable
A thread-safe, mutable sequence of characters.
A string buffer is like a String
, but can be modified. At any
point in time it contains some particular sequence of characters, but
the length and content of the sequence can be changed through certain
method calls.
String 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.
Note that while StringBuffer
is designed to be safe to use
concurrently from multiple threads, if the constructor or the
append
or insert
operation is passed a source sequence
that is shared across threads, the calling code must ensure
that the operation has a consistent and unchanging view of the source
sequence for the duration of the operation.
This could be satisfied by the caller holding a lock during the
operation's call, by using an immutable source sequence, or by not
sharing the source sequence across threads.
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.
Unless otherwise noted, passing a null
argument to a constructor
or method in this class will cause a NullPointerException
to be
thrown.
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.
Summary
Public constructors |
StringBuffer()
Constructs a string buffer with no characters in it and an
initial capacity of 16 characters.
|
StringBuffer(int capacity)
Constructs a string buffer with no characters in it and
the specified initial capacity.
|
StringBuffer(String str)
Constructs a string buffer initialized to the contents of the
specified string.
|
StringBuffer(CharSequence seq)
Constructs a string buffer that contains the same characters
as the specified CharSequence .
|
Public methods |
StringBuffer
|
append(boolean b)
|
StringBuffer
|
append(long lng)
|
StringBuffer
|
append(char c)
Appends the specified character to this Appendable.
|
StringBuffer
|
append(Object obj)
|
StringBuffer
|
append(char[] str, int offset, int len)
|
StringBuffer
|
append(double d)
|
StringBuffer
|
append(char[] str)
|
StringBuffer
|
append(String str)
|
StringBuffer
|
append(StringBuffer sb)
Appends the specified StringBuffer to this sequence.
|
StringBuffer
|
append(float f)
|
StringBuffer
|
append(int i)
|
StringBuffer
|
append(CharSequence s, int start, int end)
Appends a subsequence of the specified character sequence to this
Appendable.
|
StringBuffer
|
append(CharSequence s)
Appends the specified CharSequence to this
sequence.
|
StringBuffer
|
appendCodePoint(int codePoint)
|
int
|
capacity()
|
char
|
charAt(int index)
Returns the char value at the specified index.
|
int
|
codePointAt(int index)
|
int
|
codePointBefore(int index)
|
int
|
codePointCount(int beginIndex, int endIndex)
|
StringBuffer
|
delete(int start, int end)
|
StringBuffer
|
deleteCharAt(int index)
|
void
|
ensureCapacity(int minimumCapacity)
|
void
|
getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
|
int
|
indexOf(String str)
|
int
|
indexOf(String str, int fromIndex)
|
StringBuffer
|
insert(int offset, char[] str)
|
StringBuffer
|
insert(int offset, float f)
|
StringBuffer
|
insert(int dstOffset, CharSequence s)
|
StringBuffer
|
insert(int offset, char c)
|
StringBuffer
|
insert(int offset, long l)
|
StringBuffer
|
insert(int index, char[] str, int offset, int len)
|
StringBuffer
|
insert(int offset, int i)
|
StringBuffer
|
insert(int offset, String str)
|
StringBuffer
|
insert(int offset, double d)
|
StringBuffer
|
insert(int dstOffset, CharSequence s, int start, int end)
|
StringBuffer
|
insert(int offset, Object obj)
|
StringBuffer
|
insert(int offset, boolean b)
|
int
|
lastIndexOf(String str, int fromIndex)
|
int
|
lastIndexOf(String str)
|
int
|
length()
Returns the length of this character sequence.
|
int
|
offsetByCodePoints(int index, int codePointOffset)
|
StringBuffer
|
replace(int start, int end, String str)
|
StringBuffer
|
reverse()
|
void
|
setCharAt(int index, char ch)
|
void
|
setLength(int newLength)
|
CharSequence
|
subSequence(int start, int end)
Returns a CharSequence that is a subsequence of this sequence.
|
String
|
substring(int start, int end)
|
String
|
substring(int start)
|
String
|
toString()
Returns a string representation of the object.
|
void
|
trimToSize()
|
Inherited methods |
From class
java.lang.Object
Object
|
clone()
Creates and returns a copy of this object.
|
boolean
|
equals(Object obj)
Indicates whether some other object is "equal to" this one.
|
void
|
finalize()
Called by the garbage collector on an object when garbage collection
determines that there are no more references to the object.
|
final
Class<?>
|
getClass()
Returns the runtime class of this Object .
|
int
|
hashCode()
Returns a hash code value for the object.
|
final
void
|
notify()
Wakes up a single thread that is waiting on this object's
monitor.
|
final
void
|
notifyAll()
Wakes up all threads that are waiting on this object's monitor.
|
String
|
toString()
Returns a string representation of the object.
|
final
void
|
wait(long timeout, int nanos)
Causes the current thread to wait until another thread invokes the
notify() method or the
notifyAll() method for this object, or
some other thread interrupts the current thread, or a certain
amount of real time has elapsed.
|
final
void
|
wait(long timeout)
Causes the current thread to wait until either another thread invokes the
notify() method or the
notifyAll() method for this object, or a
specified amount of time has elapsed.
|
final
void
|
wait()
Causes the current thread to wait until another thread invokes the
notify() method or the
notifyAll() method for this object.
|
|
|
From interface
java.lang.CharSequence
abstract
char
|
charAt(int index)
Returns the char value at the specified index.
|
default
IntStream
|
chars()
Returns a stream of int zero-extending the char values
from this sequence.
|
default
IntStream
|
codePoints()
Returns a stream of code point values from this sequence.
|
abstract
int
|
length()
Returns the length of this character sequence.
|
abstract
CharSequence
|
subSequence(int start, int end)
Returns a CharSequence that is a subsequence of this sequence.
|
abstract
String
|
toString()
Returns a string containing the characters in this sequence in the same
order as this sequence.
|
|
Public constructors
StringBuffer
public StringBuffer ()
Constructs a string buffer with no characters in it and an
initial capacity of 16 characters.
StringBuffer
public StringBuffer (int capacity)
Constructs a string buffer with no characters in it and
the specified initial capacity.
Parameters |
capacity |
int : the initial capacity. |
StringBuffer
public StringBuffer (String str)
Constructs a string buffer initialized to the contents of the
specified string. The initial capacity of the string buffer is
16
plus the length of the string argument.
Parameters |
str |
String : the initial contents of the buffer. |
StringBuffer
public StringBuffer (CharSequence seq)
Constructs a string buffer that contains the same characters
as the specified 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.
Parameters |
seq |
CharSequence : the sequence to copy. |
Public methods
append
public StringBuffer append (char c)
Appends the specified character to this Appendable.
Parameters |
c |
char : The character to append |
append
public StringBuffer append (char[] str,
int offset,
int len)
Parameters |
str |
char |
offset |
int |
len |
int |
append
public StringBuffer append (StringBuffer sb)
Appends the specified StringBuffer
to this sequence.
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
).
Parameters |
sb |
StringBuffer : the StringBuffer to append. |
append
public StringBuffer append (CharSequence s,
int start,
int end)
Appends a subsequence of the specified character sequence to this
Appendable.
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))
Parameters |
s |
CharSequence : The character sequence from which a subsequence will be
appended. If csq is null, then characters
will be appended as if csq contained the four
characters "null". |
start |
int : The index of the first character in the subsequence |
end |
int : The index of the character following the last character in the
subsequence |
append
public StringBuffer append (CharSequence s)
Appends the specified 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.
Parameters |
s |
CharSequence : the CharSequence to append. |
appendCodePoint
public StringBuffer appendCodePoint (int codePoint)
capacity
public int capacity ()
charAt
public char charAt (int index)
Returns the 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.
Parameters |
index |
int : the index of the char value to be returned |
Returns |
char |
the specified char value |
codePointAt
public int codePointAt (int index)
codePointBefore
public int codePointBefore (int index)
codePointCount
public int codePointCount (int beginIndex,
int endIndex)
Parameters |
beginIndex |
int |
endIndex |
int |
delete
public StringBuffer delete (int start,
int end)
Parameters |
start |
int |
end |
int |
ensureCapacity
public void ensureCapacity (int minimumCapacity)
Parameters |
minimumCapacity |
int |
getChars
public void getChars (int srcBegin,
int srcEnd,
char[] dst,
int dstBegin)
Parameters |
srcBegin |
int |
srcEnd |
int |
dst |
char |
dstBegin |
int |
indexOf
public int indexOf (String str)
indexOf
public int indexOf (String str,
int fromIndex)
Parameters |
str |
String |
fromIndex |
int |
insert
public StringBuffer insert (int offset,
char[] str)
Parameters |
offset |
int |
str |
char |
insert
public StringBuffer insert (int offset,
float f)
Parameters |
offset |
int |
f |
float |
insert
public StringBuffer insert (int offset,
char c)
Parameters |
offset |
int |
c |
char |
insert
public StringBuffer insert (int offset,
long l)
Parameters |
offset |
int |
l |
long |
insert
public StringBuffer insert (int index,
char[] str,
int offset,
int len)
Parameters |
index |
int |
str |
char |
offset |
int |
len |
int |
insert
public StringBuffer insert (int offset,
int i)
Parameters |
offset |
int |
i |
int |
insert
public StringBuffer insert (int offset,
String str)
Parameters |
offset |
int |
str |
String |
insert
public StringBuffer insert (int offset,
double d)
Parameters |
offset |
int |
d |
double |
insert
public StringBuffer insert (int dstOffset,
CharSequence s,
int start,
int end)
Parameters |
dstOffset |
int |
s |
CharSequence |
start |
int |
end |
int |
insert
public StringBuffer insert (int offset,
Object obj)
Parameters |
offset |
int |
obj |
Object |
insert
public StringBuffer insert (int offset,
boolean b)
Parameters |
offset |
int |
b |
boolean |
lastIndexOf
public int lastIndexOf (String str,
int fromIndex)
Parameters |
str |
String |
fromIndex |
int |
lastIndexOf
public int lastIndexOf (String str)
length
public int length ()
Returns the length of this character sequence. The length is the number
of 16-bit char
s in the sequence.
Returns |
int |
the number of char s in this sequence |
offsetByCodePoints
public int offsetByCodePoints (int index,
int codePointOffset)
Parameters |
index |
int |
codePointOffset |
int |
replace
public StringBuffer replace (int start,
int end,
String str)
Parameters |
start |
int |
end |
int |
str |
String |
setCharAt
public void setCharAt (int index,
char ch)
Parameters |
index |
int |
ch |
char |
setLength
public void setLength (int newLength)
subSequence
public CharSequence subSequence (int start,
int end)
Returns a 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 char
s) of the
returned sequence is end - start, so if start == end
then an empty sequence is returned.
Parameters |
start |
int : the start index, inclusive |
end |
int : the end index, exclusive |
substring
public String substring (int start,
int end)
Parameters |
start |
int |
end |
int |
substring
public String substring (int start)
toString
public String toString ()
Returns a string representation of the object. In general, the
toString
method returns a string that
"textually represents" this object. The result should
be a concise but informative representation that is easy for a
person to read.
It is recommended that all subclasses override this method.
The toString
method for class Object
returns a string consisting of the name of the class of which the
object is an instance, the at-sign character `@
', and
the unsigned hexadecimal representation of the hash code of the
object. In other words, this method returns a string equal to the
value of:
getClass().getName() + '@' + Integer.toHexString(hashCode())
Returns |
String |
a string representation of the object. |
trimToSize
public void trimToSize ()