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JavaTM 2 Platform Std. Ed. v1.4.2 |
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java.lang.Object java.lang.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
,
Serialized FormConstructor 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(double d)
Appends the string representation of the double
argument to this string buffer. |
StringBuffer |
append(float f)
Appends the string representation of the float
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. |
StringBuffer |
append(StringBuffer sb)
Appends the specified StringBuffer to this StringBuffer. |
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 . |
int |
indexOf(String str)
Returns the index within this string of the first occurrence of the specified substring. |
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. |
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 index,
char[] str,
int offset,
int len)
Inserts the string representation of a subarray of the str
array argument into this string buffer. |
StringBuffer |
insert(int offset,
double d)
Inserts the string representation of the double
argument into this string buffer. |
StringBuffer |
insert(int offset,
float f)
Inserts the string representation of the float
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 |
lastIndexOf(String str)
Returns the index within this string of the rightmost occurrence of the specified substring. |
int |
lastIndexOf(String str,
int fromIndex)
Returns the index within this string of the last occurrence of the specified substring. |
int |
length()
Returns the length (character count) of this string buffer. |
StringBuffer |
replace(int start,
int end,
String str)
Replaces the characters in a substring of this StringBuffer
with characters in the specified String . |
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. |
CharSequence |
subSequence(int start,
int end)
Returns a new character sequence that is a subsequence of this sequence. |
String |
substring(int start)
Returns a new String that contains a subsequence of
characters currently contained in this StringBuffer .The
substring begins at the specified index and extends to the end of the
StringBuffer . |
String |
substring(int start,
int end)
Returns a new String that contains a subsequence of
characters currently contained in this StringBuffer . |
String |
toString()
Converts to a string representing the data in this string buffer. |
Methods inherited from class java.lang.Object |
clone, equals, finalize, 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.
NullPointerException
- if str
is null
Method Detail |
public int length()
length
in interface CharSequence
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 '\u0000'
.
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.
charAt
in interface CharSequence
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 index 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(StringBuffer sb)
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
.
The method ensureCapacity is first called on this StringBuffer with the new buffer length as its argument. (This ensures that the storage of this StringBuffer is adequate to contain the additional characters being appended.)
sb
- the StringBuffer to append.
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 append(float f)
float
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.
f
- a float
.
StringBuffer
object.String.valueOf(float)
,
append(java.lang.String)
public StringBuffer append(double d)
double
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.
d
- a double
.
StringBuffer
object.String.valueOf(double)
,
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 replace(int start, int end, String str)
StringBuffer
with characters in the specified String
. 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. First the
characters in the substring are removed and then the specified
String
is inserted at start
. (The
StringBuffer
will be lengthened to accommodate the
specified String if necessary.)
start
- The beginning index, inclusive.end
- The ending index, exclusive.str
- String that will replace previous contents.
StringIndexOutOfBoundsException
- if start
is negative, greater than length()
, or
greater than end
.public String substring(int start)
String
that contains a subsequence of
characters currently contained in this StringBuffer
.The
substring begins at the specified index and extends to the end of the
StringBuffer
.
start
- The beginning index, inclusive.
StringIndexOutOfBoundsException
- if start
is
less than zero, or greater than the length of this
StringBuffer
.public CharSequence subSequence(int start, int end)
An invocation of this method of the form
behaves in exactly the same way as the invocationsb.subSequence(begin, end)
This method is provided so that the StringBuffer class can implement thesb.substring(begin, end)
CharSequence
interface.
subSequence
in interface CharSequence
start
- the start index, inclusive.end
- the end index, exclusive.
IndexOutOfBoundsException
- if start or end are negative,
if end is greater than length(),
or if start is greater than endpublic String substring(int start, int end)
String
that contains a subsequence of
characters currently contained in this StringBuffer
. The
substring begins at the specified start
and
extends to the character at index end - 1
. An
exception is thrown if
start
- The beginning index, inclusive.end
- The ending index, exclusive.
StringIndexOutOfBoundsException
- if start
or end
are negative or greater than
length()
, or start
is
greater than end
.public StringBuffer insert(int index, char[] str, int offset, int len)
str
array argument into this string buffer. The subarray begins at the
specified offset
and extends len
characters.
The characters of the subarray are inserted into this string buffer at
the position indicated by index
. The length of this
StringBuffer
increases by len
characters.
index
- position at which to insert subarray.str
- A character array.offset
- the index of the first character in subarray to
to be inserted.len
- the number of characters in the subarray to
to be inserted.
StringIndexOutOfBoundsException
- if index
is negative or greater than length()
, or
offset
or len
are negative, or
(offset+len)
is greater than
str.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 insert(int offset, float f)
float
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.f
- a float
.
StringBuffer
object.
StringIndexOutOfBoundsException
- if the offset is invalid.String.valueOf(float)
,
insert(int, java.lang.String)
,
length()
public StringBuffer insert(int offset, double d)
double
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.d
- a double
.
StringBuffer
object.
StringIndexOutOfBoundsException
- if the offset is invalid.String.valueOf(double)
,
insert(int, java.lang.String)
,
length()
public int indexOf(String str)
isthis.toString().startsWith(str, k)
true
.
str
- any string.
-1
is returned.
NullPointerException
- if str
is
null
.public int indexOf(String str, int fromIndex)
If no such value of k exists, then -1 is returned.k >= Math.min(fromIndex, str.length()) && this.toString().startsWith(str, k)
str
- the substring for which to search.fromIndex
- the index from which to start the search.
NullPointerException
- if str
is
null
.public int lastIndexOf(String str)
this.length()
.
The returned index is the largest value k such that
is true.this.toString().startsWith(str, k)
str
- the substring to search for.
-1
is returned.
NullPointerException
- if str
is
null
.public int lastIndexOf(String str, int fromIndex)
If no such value of k exists, then -1 is returned.k <= Math.min(fromIndex, str.length()) && this.toString().startsWith(str, k)
str
- the substring to search for.fromIndex
- the index to start the search from.
NullPointerException
- if str
is
null
.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 interface CharSequence
toString
in class Object
|
JavaTM 2 Platform Std. Ed. v1.4.2 |
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