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SUMMARY: INNER | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD |
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
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.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 '