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java.lang.Objectjava.lang.StringBuffer
@TransactionType(value=SUPPORTS) public final class StringBuffer
A string buffer implements a 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.
String buffers are used by the compiler to implement the binary string
concatenation operator +
. For example, the code:
x = "a" + 4 + "c"
is compiled to the equivalent of:
which creates a new string buffer (initially empty), appends the string representation of each operand to the string buffer in turn, and then converts the contents of the string buffer to a string. Overall, this avoids creating many temporary strings.x = new StringBuffer().append("a").append(4).append("c").toString()
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)
.
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.
ByteArrayOutputStream
,
String
Constructor Summary | |
---|---|
StringBuffer()
Constructs a string buffer with no characters in it and an initial capacity of 16 characters. |
|
StringBuffer(int length)
Constructs a string buffer with no characters in it and an initial capacity specified by the length argument. |
|
StringBuffer(String str)
Constructs a string buffer so that it represents the same sequence of characters as the string argument; in other words, the initial contents of the string buffer is a copy of the argument string. |
Method Summary | |
---|---|
StringBuffer |
append(boolean b)
Appends the string representation of the boolean argument
to the string buffer. |
StringBuffer |
append(char c)
Appends the string representation of the char argument to
this string buffer. |
StringBuffer |
append(char[] str)
Appends the string representation of the char array
argument to this string buffer. |
StringBuffer |
append(char[] str,
int offset,
int len)
Appends the string representation of a subarray of the char
array argument to this string buffer. |
StringBuffer |
append(int i)
Appends the string representation of the int argument to
this string buffer. |
StringBuffer |
append(long l)
Appends the string representation of the long argument to
this string buffer. |
StringBuffer |
append(Object obj)
Appends the string representation of the Object argument
to this string buffer. |
StringBuffer |
append(String str)
Appends the string to this string buffer. |
int |
capacity()
Returns the current capacity of the String buffer. |
char |
charAt(int index)
The specified character of the sequence currently represented by the string buffer, as indicated by the index argument, is
returned. |
StringBuffer |
delete(int start,
int end)
Removes the characters in a substring of this StringBuffer . |
StringBuffer |
deleteCharAt(int index)
Removes the character at the specified position in this StringBuffer (shortening the StringBuffer
by one character). |
void |
ensureCapacity(int minimumCapacity)
Ensures that the capacity of the buffer is at least equal to the specified minimum. |
void |
getChars(int srcBegin,
int srcEnd,
char[] dst,
int dstBegin)
Characters are copied from this string buffer into the destination character array dst . |
StringBuffer |
insert(int offset,
boolean b)
Inserts the string representation of the boolean argument
into this string buffer. |
StringBuffer |
insert(int offset,
char c)
Inserts the string representation of the char argument
into this string buffer. |
StringBuffer |
insert(int offset,
char[] str)
Inserts the string representation of the char array
argument into this string buffer. |
StringBuffer |
insert(int offset,
int i)
Inserts the string representation of the second int
argument into this string buffer. |
StringBuffer |
insert(int offset,
long l)
Inserts the string representation of the long argument
into this string buffer. |
StringBuffer |
insert(int offset,
Object obj)
Inserts the string representation of the Object argument
into this string buffer. |
StringBuffer |
insert(int offset,
String str)
Inserts the string into this string buffer. |
int |
length()
Returns the length (character count) of this string buffer. |
StringBuffer |
reverse()
The character sequence contained in this string buffer is replaced by the reverse of the sequence. |
void |
setCharAt(int index,
char ch)
The character at the specified index of this string buffer is set to ch . |
void |
setLength(int newLength)
Sets the length of this string buffer. |
String |
toString()
Converts to a string representing the data in this string buffer. |
Methods inherited from class java.lang.Object |
---|
equals, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Constructor Detail |
---|
public StringBuffer()
public StringBuffer(int length)
length
argument.
length
- the initial capacity.
NegativeArraySizeException
- if the length
argument is less than
0
.public StringBuffer(String str)
16
plus the length of the
string argument.
str
- the initial contents of the buffer.Method Detail |
---|
public int length()
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 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 ' '
.
In other words, if the newLength
argument is less than the
current length of the string buffer, the string buffer is truncated to
contain exactly the number of characters given by the
newLength
argument.
If the newLength
argument is greater than or equal to the
current length, sufficient null characters ('\u0000'
)
are appended to the string buffer so that length becomes the
newLength
argument.
The newLength
argument must be greater than or equal to
0
.
newLength
- the new length of the buffer.
IndexOutOfBoundsException
- if the newLength
argument is negative.length()
public char charAt(int index)
index
argument, is
returned. The first character of a string buffer is at index
0
, the next at index 1
, and so on, for
array indexing.
The index argument must be greater than or equal to 0
,
and less than the length of this string buffer.
index
- the index of the desired character.
IndexOutOfBoundsException
- if index
is negative or greater than or
equal to length()
.length()
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 in the string buffer.srcEnd
- stop copying at this offset in the string buffer.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()
, the current length of this
string buffer.
dstBegin+srcEnd-srcBegin
is greater
than dst.length
public void setCharAt(int index, char ch)
ch
. The string buffer 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 offset argument must be greater than or equal to 0
,
and less than the length of this string buffer.
index
- the index of the character to modify.ch
- the new character.
IndexOutOfBoundsException
- if index
is negative or greater than or
equal to length()
.length()
public StringBuffer append(Object obj)
Object
argument
to this string buffer.
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 buffer.
obj
- an Object
.
StringBuffer
object.String.valueOf(java.lang.Object)
,
append(java.lang.String)
public StringBuffer append(String str)
The characters of the String
argument are appended, in
order, to the contents of this string buffer, increasing the length of
this string buffer by the length of the argument. If str
is null
, then the four characters "null"
are appended to this string buffer.
Let n be the length of the old character sequence, the one
contained in the string buffer 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.
StringBuffer
.public StringBuffer append(char[] str)
char
array
argument to this string buffer.
The characters of the array argument are appended, in order, to the contents of this string buffer. The length of this string buffer 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
StringBuffer
object.
str
- the characters to be appended.
StringBuffer
object.public StringBuffer append(char[] str, int offset, int len)
char
array argument to this string buffer.
Characters of the character array str
, starting at index
offset
, are appended, in order, to the contents of this
string buffer. The length of this string buffer 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 StringBuffer
object.
str
- the characters to be appended.offset
- the index of the first character to append.len
- the number of characters to append.
StringBuffer
object.public StringBuffer append(boolean b)
boolean
argument
to the string buffer.
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 buffer.
b
- a boolean
.
StringBuffer
.String.valueOf(boolean)
,
append(java.lang.String)
public StringBuffer append(char c)
char
argument to
this string buffer.
The argument is appended to the contents of this string buffer. The
length of this string buffer 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
StringBuffer
object.
c
- a char
.
StringBuffer
object.public StringBuffer append(int i)
int
argument to
this string buffer.
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 buffer.
i
- an int
.
StringBuffer
object.String.valueOf(int)
,
append(java.lang.String)
public StringBuffer append(long l)
long
argument to
this string buffer.
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 buffer.
l
- a long
.
StringBuffer
object.String.valueOf(long)
,
append(java.lang.String)
public StringBuffer delete(int start, int end)
StringBuffer
.
The substring begins at the specified start
and extends to
the character at index end - 1
or to the end of the
StringBuffer
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.
StringIndexOutOfBoundsException
- if start
is negative, greater than
length()
, or greater than end
.public StringBuffer deleteCharAt(int index)
StringBuffer
(shortening the StringBuffer
by one character).
index
- Index of character to remove
StringIndexOutOfBoundsException
- if the index
is negative or greater than or
equal to length()
.public StringBuffer insert(int offset, Object obj)
Object
argument
into this string buffer.
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 string buffer 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 string buffer.
offset
- the offset.obj
- an Object
.
StringBuffer
object.
StringIndexOutOfBoundsException
- if the offset is invalid.String.valueOf(java.lang.Object)
,
insert(int, java.lang.String)
,
length()
public StringBuffer insert(int offset, String str)
The characters of the String
argument are inserted, in
order, into this string buffer at the indicated offset, moving up any
characters originally above that position and increasing the length of
this string buffer by the length of the argument. If str
is null
, then the four characters "null"
are inserted into this string buffer.
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 string buffer.
offset
- the offset.str
- a string.
StringBuffer
object.
StringIndexOutOfBoundsException
- if the offset is invalid.length()
public StringBuffer insert(int offset, char[] str)
char
array
argument into this string buffer.
The characters of the array argument are inserted into the contents of
this string buffer at the position indicated by offset
.
The length of this string buffer 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
StringBuffer
object at the position indicated by
offset
.
offset
- the offset.str
- a character array.
StringBuffer
object.
StringIndexOutOfBoundsException
- if the offset is invalid.public StringBuffer insert(int offset, boolean b)
boolean
argument
into this string buffer.
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 string buffer 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 string buffer.
offset
- the offset.b
- a boolean
.
StringBuffer
object.
StringIndexOutOfBoundsException
- if the offset is invalid.String.valueOf(boolean)
,
insert(int, java.lang.String)
,
length()
public StringBuffer insert(int offset, char c)
char
argument
into this string buffer.
The second argument is inserted into the contents of this string buffer
at the position indicated by offset
. The length of this
string buffer 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
StringBuffer
object 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 string buffer.
offset
- the offset.c
- a char
.
StringBuffer
object.
IndexOutOfBoundsException
- if the offset is invalid.length()
public StringBuffer insert(int offset, int i)
int
argument into this string buffer.
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 string buffer 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 string buffer.
offset
- the offset.i
- an int
.
StringBuffer
object.
StringIndexOutOfBoundsException
- if the offset is invalid.String.valueOf(int)
,
insert(int, java.lang.String)
,
length()
public StringBuffer insert(int offset, long l)
long
argument
into this string buffer.
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 string buffer 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 string buffer.
offset
- the offset.l
- a long
.
StringBuffer
object.
StringIndexOutOfBoundsException
- if the offset is invalid.String.valueOf(long)
,
insert(int, java.lang.String)
,
length()
public StringBuffer reverse()
Let n be the length of the old character sequence, the one
contained in the string buffer 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.
StringBuffer
object..public String toString()
String
object is allocated and initialized to contain the
character sequence currently represented by this string buffer. This
String
is then returned. Subsequent changes to the string
buffer do not affect the contents of the String
.
Implementation advice: This method can be coded so as to create a new
String
object without allocating new memory to hold a copy
of the character sequence. Instead, the string can share the memory used
by the string buffer. Any subsequent operation that alters the content or
capacity of the string buffer must then make a copy of the internal
buffer at that time. This strategy is effective for reducing the amount
of memory allocated by a string concatenation operation when it is
implemented using a string buffer.
toString
in class Object
|
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