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java.lang.Objectjava.lang.StringBuilder
public final class StringBuilder
A mutable sequence of characters. This class provides an API
compatible with StringBuffer
, but with no guarantee of
synchronization. This class is designed for use as a drop-in
replacement for StringBuffer
in places where the string
buffer was being used by a single thread (as is generally the
case). Where possible, it is recommended that this class be used in
preference to StringBuffer
as it will be faster under most
implementations.
A string builder implements a mutable sequence of characters.
A string builder 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 builders 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 builder (initially empty), appends the string representation of each operand to the string builder in turn, and then converts the contents of the string builder to a string. Overall, this avoids creating many temporary strings.x = new StringBuilder().append("a").append(4).append("c") .toString()
The principal operations on a StringBuilder
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 builder. The
append
method always adds these characters at the end
of the builder; the insert
method adds the characters at
a specified point.
For example, if z
refers to a string builder object
whose current contents are "start
", then
the method call z.append("le")
would cause the string
builder to contain "startle
", whereas
z.insert(4, "le")
would alter the string builder to
contain "starlet
".
In general, if sb refers to an instance of a StringBuilder
,
then sb.append(x)
has the same effect as
sb.insert(sb.length(), x)
.
Every string builder has a capacity. As long as the length of the character sequence contained in the string builder 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
,
StringBuffer
Constructor Summary | |
---|---|
StringBuilder()
Constructs a string builder with no characters in it and an initial capacity of 16 characters. |
|
StringBuilder(int length)
Constructs a string builder with no characters in it and an initial capacity specified by the length argument. |
|
StringBuilder(String s)
Constructs a string builder so that it represents the same sequence of characters as the string argument; in other words, the initial contents of the string builder is a copy of the argument string. |
Method Summary | |
---|---|
StringBuilder |
append(boolean b)
Appends the string representation of the boolean
argument to the string builder. |
StringBuilder |
append(char c)
Appends the string representation of the char
argument to this string builder. |
StringBuilder |
append(char[] chars)
Appends the string representation of the char array
argument to this string builder. |
StringBuilder |
append(char[] chars,
int offset,
int len)
Appends the string representation of a subarray of the char array argument to this string builder. |
StringBuilder |
append(double d)
Appends the string representation of the double
argument to this string builder. |
StringBuilder |
append(float f)
Appends the string representation of the float
argument to this string builder. |
StringBuilder |
append(int i)
Appends the string representation of the int
argument to this string builder. |
StringBuilder |
append(long l)
Appends the string representation of the long
argument to this string builder. |
StringBuilder |
append(Object aObject)
Appends the string representation of the Object
argument to this string builder. |
StringBuilder |
append(String s)
Appends the string to this string builder. |
int |
capacity()
Returns the current capacity of the string builder. |
char |
charAt(int i)
The specified character of the sequence currently represented by the string builder, as indicated by the index argument,
is returned. |
StringBuilder |
delete(int start,
int end)
Removes the characters in a substring of this StringBuilder . |
StringBuilder |
deleteCharAt(int index)
Removes the character at the specified position in this StringBuilder (shortening the StringBuilder
by one character). |
void |
ensureCapacity(int capacity)
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 builder into the destination character array dst . |
StringBuilder |
insert(int offset,
boolean b)
Inserts the string representation of the boolean
argument into this string builder. |
StringBuilder |
insert(int offset,
char c)
Inserts the string representation of the char
argument into this string builder. |
StringBuilder |
insert(int offset,
char[] chars)
Inserts the string representation of the char array
argument into this string builder. |
StringBuilder |
insert(int offset,
double d)
Inserts the string representation of the double
argument into this string builder. |
StringBuilder |
insert(int offset,
float f)
Inserts the string representation of the float
argument into this string builder. |
StringBuilder |
insert(int offset,
int i)
Inserts the string representation of the second int
argument into this string builder. |
StringBuilder |
insert(int offset,
long l)
Inserts the string representation of the long
argument into this string builder. |
StringBuilder |
insert(int offset,
Object obj)
Inserts the string representation of the Object
argument into this string builder. |
StringBuilder |
insert(int offset,
String s)
Inserts the string into this string builder. |
int |
length()
Returns the length (character count) of this string builder. |
StringBuilder |
reverse()
The character sequence contained in this string builder is replaced by the reverse of the sequence. |
void |
setCharAt(int index,
char c)
The character at the specified index of this string builder is set to ch . |
void |
setLength(int length)
Sets the length of this string builder. |
String |
toString()
Converts to a string representing the data in this string builder. |
Methods inherited from class java.lang.Object |
---|
equals, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Constructor Detail |
---|
public StringBuilder()
public StringBuilder(int length)
length
argument.
length
- the initial capacity.
NegativeArraySizeException
- if the length
argument is less than 0
.public StringBuilder(String s)
16
plus the length of the string argument.
s
- the initial contents of the builder.Method Detail |
---|
public int length()
public int capacity()
public void ensureCapacity(int capacity)
minimumCapacity
argument.
2
.
minimumCapacity
argument is nonpositive, this
method takes no action and simply returns.
capacity
- the minimum desired capacity.public void setLength(int length)
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 builder, the string builder 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 builder so that
length becomes the newLength
argument.
The newLength
argument must be greater than or equal
to 0
.
length
- the new length of the buffer.
IndexOutOfBoundsException
- if the
newLength
argument is negative.length()
public char charAt(int i)
index
argument,
is returned. The first character of a string builder 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 builder.
i
- the index of the desired character.
IndexOutOfBoundsException
- if index
is
negative or greater than or equal to length()
.length()
public void setCharAt(int index, char c)
ch
. The string builder 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 builder.
index
- the index of the character to modify.c
- the new 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 builder.srcEnd
- stop copying at this offset in the string builder.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 builder.
dstBegin+srcEnd-srcBegin
is greater than
dst.length
public StringBuilder insert(int offset, String s)
The characters of the String
argument are inserted, in
order, into this string builder at the indicated offset, moving up any
characters originally above that position and increasing the length
of this string builder by the length of the argument. If
str
is null
, then the four characters
"null"
are inserted into this string builder.
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 builder.
offset
- the offset.s
- a string.
StringBuilder
object.
StringIndexOutOfBoundsException
- if the offset is invalid.length()
public StringBuilder insert(int offset, Object obj)
Object
argument into this string builder.
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 builder 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 builder.
offset
- the offset.obj
- an Object
.
StringBuilder
object.
StringIndexOutOfBoundsException
- if the offset is invalid.String.valueOf(java.lang.Object)
,
insert(int, java.lang.String)
,
length()
public StringBuilder insert(int offset, char[] chars)
char
array
argument into this string builder.
The characters of the array argument are inserted into the
contents of this string builder at the position indicated by
offset
. The length of this string builder 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
StringBuilder
object at the position indicated by
offset
.
offset
- the offset.chars
- a character array.
StringBuilder
object.
StringIndexOutOfBoundsException
- if the offset is invalid.public StringBuilder insert(int offset, boolean b)
boolean
argument into this string builder.
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 builder 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 builder.
offset
- the offset.b
- a boolean
.
StringBuilder
object.
StringIndexOutOfBoundsException
- if the offset is invalid.String.valueOf(boolean)
,
insert(int, java.lang.String)
,
length()
public StringBuilder insert(int offset, char c)
char
argument into this string builder.
The second argument is inserted into the contents of this string
builder at the position indicated by offset
. The length
of this string builder 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 StringBuilder
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 builder.
offset
- the offset.c
- a char
.
StringBuilder
object.
IndexOutOfBoundsException
- if the offset is invalid.length()
public StringBuilder insert(int offset, int i)
int
argument into this string builder.
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 builder 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 builder.
offset
- the offset.i
- an int
.
StringBuilder
object.
StringIndexOutOfBoundsException
- if the offset is invalid.String.valueOf(int)
,
insert(int, java.lang.String)
,
length()
public StringBuilder insert(int offset, long l)
long
argument into this string builder.
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 builder 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 builder.
offset
- the offset.l
- a long
.
StringBuilder
object.
StringIndexOutOfBoundsException
- if the offset is invalid.String.valueOf(long)
,
insert(int, java.lang.String)
,
length()
public StringBuilder insert(int offset, float f)
float
argument into this string builder.
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 builder 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 builder.
offset
- the offset.f
- a float
.
StringBuilder
object.
StringIndexOutOfBoundsException
- if the offset is invalid.String.valueOf(float)
,
insert(int, java.lang.String)
,
length()
public StringBuilder insert(int offset, double d)
double
argument into this string builder.
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 builder 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 builder.
offset
- the offset.d
- a double
.
StringBuilder
object.
StringIndexOutOfBoundsException
- if the offset is invalid.String.valueOf(double)
,
insert(int, java.lang.String)
,
length()
public StringBuilder append(String s)
The characters of the String
argument are appended, in
order, to the contents of this string builder, increasing the
length of this string builder by the length of the argument.
If str
is null
, then the four characters
"null"
are appended to this string builder.
Let n be the length of the old character sequence, the one
contained in the string builder 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
.
s
- a string.
StringBuilder
.public StringBuilder append(Object aObject)
Object
argument to this string builder.
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 builder.
aObject
- an Object
.
StringBuilder
object.String.valueOf(java.lang.Object)
,
append(java.lang.String)
public StringBuilder append(char[] chars, int offset, int len)
char
array argument to this string builder.
Characters of the character array str
, starting at
index offset
, are appended, in order, to the contents
of this string builder. The length of this string builder 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 StringBuilder
object.
chars
- the characters to be appended.offset
- the index of the first character to append.len
- the number of characters to append.
StringBuilder
object.public StringBuilder append(char[] chars)
char
array
argument to this string builder.
The characters of the array argument are appended, in order, to the contents of this string builder. 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 StringBuilder
object.
chars
- the characters to be appended.
StringBuilder
object.public StringBuilder append(boolean b)
boolean
argument to the string builder.
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 builder.
b
- a boolean
.
StringBuilder
.String.valueOf(boolean)
,
append(java.lang.String)
public StringBuilder append(char c)
char
argument to this string builder.
The argument is appended to the contents of this string builder.
The length of this string builder 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
StringBuilder
object.
c
- a char
.
StringBuilder
object.public StringBuilder append(int i)
int
argument to this string builder.
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 builder.
i
- an int
.
StringBuilder
object.String.valueOf(int)
,
append(java.lang.String)
public StringBuilder append(long l)
long
argument to this string builder.
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 builder.
l
- a long
.
StringBuilder
object.String.valueOf(long)
,
append(java.lang.String)
public StringBuilder append(double d)
double
argument to this string builder.
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 builder.
d
- a double
.
StringBuilder
object.String.valueOf(double)
,
append(java.lang.String)
public StringBuilder append(float f)
float
argument to this string builder.
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 builder.
f
- a float
.
StringBuilder
object.String.valueOf(float)
,
append(java.lang.String)
public StringBuilder delete(int start, int end)
StringBuilder
.
The substring begins at the specified start
and extends to
the character at index end - 1
or to the end of the
StringBuilder
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 StringBuilder deleteCharAt(int index)
StringBuilder
(shortening the StringBuilder
by one character).
index
- Index of character to remove
StringIndexOutOfBoundsException
- if the index
is negative or greater than or equal to
length()
.public StringBuilder reverse()
Let n be the length of the old character sequence, the one
contained in the string builder 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.
StringBuilder
object..public String toString()
String
object is allocated and initialized to
contain the character sequence currently represented by this
string builder. This String
is then returned. Subsequent
changes to the string builder 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 builder. Any subsequent operation that alters
the content or capacity of the string builder 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 builder.
toString
in class Object
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