implements Appendable CharSequence Serializable CharSequence
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.
See Also
Public Constructor Summary
|
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 Method Summary
| StringBuffer |
append(boolean b)
|
| synchronized StringBuffer |
append(long lng)
|
| synchronized StringBuffer |
append(char c)
Appends the specified character to this Appendable.
|
| StringBuffer | |
| synchronized StringBuffer |
append(char[] str, int offset, int len)
|
| synchronized StringBuffer |
append(double d)
|
| synchronized StringBuffer |
append(char[] str)
|
| synchronized StringBuffer | |
| synchronized StringBuffer | |
| synchronized StringBuffer |
append(float f)
|
| synchronized StringBuffer |
append(int i)
|
| synchronized StringBuffer |
append(CharSequence s, int start, int end)
Appends a subsequence of the specified character sequence to this
Appendable.
|
| synchronized StringBuffer | |
| StringBuffer |
appendCodePoint(int codePoint)
|
| synchronized int |
capacity()
|
| synchronized char |
charAt(int index)
Returns the
char value at the specified index. |
| synchronized int |
codePointAt(int index)
|
| synchronized int |
codePointBefore(int index)
|
| synchronized int |
codePointCount(int beginIndex, int endIndex)
|
| synchronized StringBuffer |
delete(int start, int end)
|
| synchronized StringBuffer |
deleteCharAt(int index)
|
| synchronized void |
ensureCapacity(int minimumCapacity)
|
| synchronized void |
getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
|
| int | |
| synchronized int | |
| synchronized StringBuffer |
insert(int offset, char[] str)
|
| StringBuffer |
insert(int offset, float f)
|
| StringBuffer |
insert(int dstOffset, CharSequence s)
|
| synchronized StringBuffer |
insert(int offset, char c)
|
| StringBuffer |
insert(int offset, long l)
|
| synchronized StringBuffer |
insert(int index, char[] str, int offset, int len)
|
| StringBuffer |
insert(int offset, int i)
|
| synchronized StringBuffer | |
| StringBuffer |
insert(int offset, double d)
|
| synchronized StringBuffer |
insert(int dstOffset, CharSequence s, int start, int end)
|
| StringBuffer | |
| StringBuffer |
insert(int offset, boolean b)
|
| synchronized int |
lastIndexOf(String str, int fromIndex)
|
| int | |
| synchronized int |
length()
Returns the length of this character sequence.
|
| synchronized int |
offsetByCodePoints(int index, int codePointOffset)
|
| synchronized StringBuffer | |
| synchronized StringBuffer |
reverse()
|
| synchronized void |
setCharAt(int index, char ch)
|
| synchronized void |
setLength(int newLength)
|
| synchronized CharSequence |
subSequence(int start, int end)
Returns a
CharSequence that is a subsequence of this sequence. |
| synchronized String |
substring(int start, int end)
|
| synchronized String |
substring(int start)
|
| synchronized String |
toString()
Returns a string containing a concise, human-readable description of this
object.
|
| synchronized void |
Inherited Method Summary
Public Constructors
public StringBuffer ()
Constructs a string buffer with no characters in it and an initial capacity of 16 characters.
public StringBuffer (int capacity)
Constructs a string buffer with no characters in it and the specified initial capacity.
Parameters
| capacity | the initial capacity. |
|---|
Throws
| NegativeArraySizeException | if the capacity
argument is less than 0.
|
|---|
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 | the initial contents of the buffer. |
|---|
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 | the sequence to copy. |
|---|
Public Methods
public synchronized StringBuffer append (char c)
Appends the specified character to this Appendable.
Parameters
| c | The character to append |
|---|
Returns
- A reference to this Appendable
public synchronized StringBuffer append (char[] str, int offset, int len)
public synchronized 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 | the StringBuffer to append. |
|---|
Returns
- a reference to this object.
public synchronized 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 | 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 | The index of the first character in the subsequence |
| end | The index of the character following the last character in the subsequence |
Returns
- A reference to this Appendable
Throws
| IndexOutOfBoundsException |
|---|
public synchronized 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 | the CharSequence to append. |
|---|
Returns
- a reference to this object.
public synchronized int capacity ()
public synchronized 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 | the index of the char value to be returned |
|---|
Returns
- the specified
charvalue
Throws
| IndexOutOfBoundsException |
|---|
See Also
public synchronized int codePointAt (int index)
Parameters
| index |
|---|
public synchronized int codePointBefore (int index)
Parameters
| index |
|---|
public synchronized int codePointCount (int beginIndex, int endIndex)
Parameters
| beginIndex | |
|---|---|
| endIndex |
public synchronized StringBuffer delete (int start, int end)
public synchronized StringBuffer deleteCharAt (int index)
public synchronized void ensureCapacity (int minimumCapacity)
Parameters
| minimumCapacity |
|---|
public synchronized void getChars (int srcBegin, int srcEnd, char[] dst, int dstBegin)
public synchronized StringBuffer insert (int offset, char[] str)
public StringBuffer insert (int offset, float f)
public StringBuffer insert (int dstOffset, CharSequence s)
public synchronized StringBuffer insert (int offset, char c)
public StringBuffer insert (int offset, long l)
public synchronized StringBuffer insert (int index, char[] str, int offset, int len)
public StringBuffer insert (int offset, int i)
public synchronized StringBuffer insert (int offset, String str)
public StringBuffer insert (int offset, double d)
public synchronized StringBuffer insert (int dstOffset, CharSequence s, int start, int end)
public StringBuffer insert (int offset, Object obj)
public StringBuffer insert (int offset, boolean b)
public synchronized int length ()
Returns the length of this character sequence. The length is the number
of 16-bit chars in the sequence.
Returns
- the number of
chars in this sequence
public synchronized int offsetByCodePoints (int index, int codePointOffset)
Parameters
| index | |
|---|---|
| codePointOffset |
public synchronized StringBuffer replace (int start, int end, String str)
public synchronized void setCharAt (int index, char ch)
public synchronized void setLength (int newLength)
public synchronized 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 chars) of the
returned sequence is end - start, so if start == end
then an empty sequence is returned.
Parameters
| start | the start index, inclusive |
|---|---|
| end | the end index, exclusive |
Returns
- the specified subsequence
Throws
| IndexOutOfBoundsException |
|---|
public synchronized String substring (int start, int end)
public synchronized String substring (int start)
public synchronized String toString ()
Returns a string containing a concise, human-readable description of this object. Subclasses are encouraged to override this method and provide an implementation that takes into account the object's type and data. The default implementation is equivalent to the following expression:
getClass().getName() + '@' + Integer.toHexString(hashCode())
See Writing a useful
toString method
if you intend implementing your own toString method.
Returns
- a printable representation of this object.