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
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
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
the method call
z.append("le") would cause the string
buffer to contain
z.insert(4, "le") would alter the string buffer to
In general, if sb refers to an instance of a
sb.append(x) has the same effect as
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
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
As of release JDK 5, this class has been supplemented with an equivalent
class designed for use by a single thread,
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.
Public Constructor Summary
Constructs a string buffer with no characters in it and an initial capacity of 16 characters.
Constructs a string buffer with no characters in it and the specified initial capacity.