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§1.17 Class StringBuffer

public  class  java.lang.StringBuffer
    extends  java.lang.Object  (I-§1.12)
{
        // Constructors
    public StringBuffer();	§1.17.1
    public StringBuffer(int  length);	§1.17.2
    public StringBuffer(String  str);	§1.17.3

        // Methods
    public StringBuffer append(boolean  b);	§1.17.4
    public StringBuffer append(char  c);	§1.17.5
    public StringBuffer append(char  str[]);	§1.17.6
    public StringBuffer 	§1.17.7
                      append(char  str[], int  offset, int  len);
    public StringBuffer append(double  d);	§1.17.8
    public StringBuffer append(float  f);	§1.17.9
    public StringBuffer append(int  i);	§1.17.10
    public StringBuffer append(long  l);	§1.17.11
    public StringBuffer append(Object  obj);	§1.17.12
    public StringBuffer append(String  str);	§1.17.13
    public int capacity();	§1.17.14
    public char charAt(int  index);	§1.17.15
    public void ensureCapacity(int  minimumCapacity);	§1.17.16
    public void getChars(int  srcBegin, int  srcEnd,	§1.17.17
                                char  dst[], int  dstBegin);
    public StringBuffer insert(int  offset, boolean  b);	§1.17.18
    public StringBuffer insert(int  offset, char  c);	§1.17.19
    public StringBuffer insert(int  offset, char  str[]);	§1.17.20
    public StringBuffer insert(int  offset, double  d);	§1.17.21
    public StringBuffer insert(int  offset, float  f);	§1.17.22
    public StringBuffer insert(int  offset, int  i);	§1.17.23 
    public StringBuffer insert(int  offset, long  l);	§1.17.24
    public StringBuffer insert(int  offset, Object  obj);	§1.17.25
    public StringBuffer insert(int  offset, String  str);	§1.17.26
    public int length();	§1.17.27
    public StringBuffer reverse();	§1.17.28
    public void setCharAt(int  index, char  ch);	§1.17.29
    public void setLength(int  newLength);	§1.17.30
    public String toString();	§1.17.31
}

A string buffer implements a mutable sequence of characters.

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.

String buffers are used by the compiler to implement the binary string concatentation operator +. For example the code

x = "a"  +  4  +  "c"

is compiled to the equivalent of:

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" while z.insert(4, "le") would alter the string buffer to contain "starlet".

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.


See Also:: String (I-§1.16)
ByteArrayOutputStream (I-§2.4).

StringBuffer

public StringBuffer()

Constructs a string buffer with no characters in it, and an initial capacity of 16 characters.

StringBuffer

public StringBuffer(int  length)

Constructs a string buffer with no characters in it, and an initial capacity specified by the length argument.

Parameters:: length -the initial capacity
Throws: NegativeArraySizeException (I-§1.38); If the length argument is less than zero.

StringBuffer

public StringBuffer(String  str)

Constructs a string buffer so that it represents the same sequence of characters as the string argument. The initial capacity of the string buffer is 16 plus the length of the string argument.

Parameters:: str -the initial contents of the buffer

append

public StringBuffer append(boolean  b)

Appends the string representation of the boolean argument to the string buffer.

The argument is converted to a string as if by the method String.valueOf (I-§1.16.41), and the characters of that string are then appended (I-§1.17.13) to this string buffer.

Parameters:: b -a boolean
Returns:: this string buffer

append

public StringBuffer append(char  c)

Appends the string representation of the 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 one.

Parameters:: ch -a char
Returns:: this string buffer

append

public StringBuffer append(char  str[])

Appends the string representation of the 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.

Parameters:: str -the characters to be appended
Returns:: this string buffer

append

public StringBuffer append(char  str[], int  offset, int  len)

Appends the string representation of a subarray of the 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.

Parameters:: str -the characters to be appended; offset -index of first character to append; len -the number of characters to aappend
Returns:: this string buffer

append

public StringBuffer append(double  d)

Appends the string representation of the double argument to this string buffer.

The argument is converted to a string as if by the method String.valueOf (I-§1.16.45), and the characters of that string are then appended (I-§1.17.13) to this string buffer.

Parameters:: d -a double
Returns:: this string buffer

append

public StringBuffer append(float  f)

Appends the string representation of the float argument to this string buffer.

The argument is converted to a string as if by the method String.valueOf (I-§1.16.46), and the characters of that string are then appended (I-§1.17.13) to this string buffer.

Parameters:: f -a float
Returns:: this string buffer.

append

public StringBuffer append(int  i)

Appends the string representation of the int argument to this string buffer.

The argument is converted to a string as if by the method String.valueOf (I-§1.16.47), and the characters of that string are then appended (I-§1.17.13) to this string buffer.

Parameters:: i -an int
Returns:: this string buffer.

append

public StringBuffer append(long  l)

Appends the string representation of the long argument to this string buffer.

The argument is converted to a string as if by the method String.valueOf (I-§1.16.48), and the characters of that string are then appended (I-§1.17.13) to this string buffer.

Parameters:: l -a long
Returns:: this string buffer.

append

public StringBuffer append(Object  obj)

Appends the string representation of the Object argument to this string buffer.

The argument is converted to a string as if by the method String.valueOf (I-§1.17.3), and the characters of that string are then appended (I-§1.17.13) to this string buffer.

Parameters:: obj -an Object
Returns:: this string buffer.

append

public StringBuffer append(String  str)

Appends the string to this string buffer.

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.

Parameters:: str -a string
Returns:: this string buffer.

capacity

public int capacity()

Returns:: the current capacity of this string buffer.

charAt

public char charAt(int  index)

Determines the character at a specific index in this string buffer.

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 (I-§1.17.27) of this string buffer.

Parameters:: index -the index of the desired character
Returns:: the character at the specified index of this string buffer.
Throws: StringIndexOutOfBoundsException (I-§1.44); If the index is invalid.

ensureCapacity

public void ensureCapacity(int  minimumCapacity)

If the current capacity of this string buffer is less than the argument, then a new internal buffer is allocated with greater capacity. The new capacity is the larger of:

the minimumCapacity argument

twice the old capacity, plus 2

If the minimumCapacity argument is nonpositive, this method takes no action and simply returns.

Parameters:: minimumCapacity -the minimum desired capacity

getChars

public void getChars(int  srcBegin, int  srcEnd,                                         char  dst[],  int  dstBegin)

Characters are copied from this string buffer into the destination character array 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.

Parameters:: srcBegin -begin copy 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
Throws: StringIndexOutOfBoundsException (I-§1.44); If there is an invalid index into the buffer.

insert

public StringBuffer insert(int  offset, boolean  b)

Inserts the string representation of the boolean argument into this string buffer.

The second argument is converted to a string as if by the method String.valueOf (I-§1.16.41), and the characters of that string are then inserted (I-§1.17.26) 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 (I-§1.17.27) of this string buffer.

Parameters:: offset -the offset; b -a boolean
Returns:: this string buffer.
Throws: StringIndexOutOfBoundsException (I-§1.44); If the offset is invalid.

insert

public StringBuffer  insert(int  offset, char  c)

Inserts the string representation of the 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 offset argument must be greater than or equal to 0, and less than or equal to the length (I-§1.17.27) of this string buffer.

Parameters:: offset -the offset; ch -a char
Returns:: this string buffer.
Throws: StringIndexOutOfBoundsException (I-§1.44); If the offset is invalid.

insert

public StringBuffer insert(int  offset, char  str[])

Inserts the string representation of the 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.

Parameters:: offset -the offset; ch -a character array
Returns:: this string buffer.
Throws: StringIndexOutOfBoundsException (I-§1.44); If the offset is invalid.

insert

public StringBuffer insert(int  offset, double  d)

Inserts the string representation of the double argument into this string buffer.

The second argument is converted to a string as if by the method String.valueOf (I-§1.16.45), and the characters of that string are then inserted (I-§1.17.26) 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 (I-§1.17.27) of this string buffer.

Parameters:: offset -the offset; b -a double
Returns:: this string buffer.
Throws: StringIndexOutOfBoundsException (I-§1.44); If the offset is invalid.

insert

public StringBuffer insert(int  offset, float  f)

Inserts the string representation of the float argument into this string buffer.

The second argument is converted to a string as if by the method String.valueOf (I-§1.16.46), and the characters of that string are then inserted (I-§1.17.26) 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 (I-§1.17.27) of this string buffer.

Parameters:: offset -the offset; b -a float
Returns:: this string buffer.
Throws: StringIndexOutOfBoundsException (I-§1.44); If the offset is invalid.

insert

public StringBuffer insert(int  offset, int  i)

Inserts the string representation of the second int argument into this string buffer.

The second argument is converted to a string as if by the method String.valueOf (I-§1.16.47), and the characters of that string are then inserted (I-§1.17.26) 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 (I-§1.17.27) of this string buffer.

Parameters:: offset -the offset; b -an int
Returns:: this string buffer.
Throws: StringIndexOutOfBoundsException (I-§1.44); If the offset is invalid.

insert

public StringBuffer insert(int  offset, long  l)

Inserts the string representation of the long argument into this string buffer.

The second argument is converted to a string as if by the method String.valueOf (I-§1.16.48), and the characters of that string are then inserted (I-§1.17.26) 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 (I-§1.17.27) of this string buffer.

Parameters:: offset -the offset; b -a long
Returns:: this string buffer.
Throws: StringIndexOutOfBoundsException (I-§1.44); If the offset is invalid.

insert

public StringBuffer  insert(int  offset, Object  obj)

Inserts the string representation of the Object argument into this string buffer.

The second argument is converted to a string as if by the method String.valueOf (I-§1.16.49), and the characters of that string are then inserted (I-§1.17.26) 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 (I-§1.17.27) of this string buffer.

Parameters:: offset -the offset; b -an Object
Returns:: this string buffer.
Throws: StringIndexOutOfBoundsException (I-§1.44); If the offset is invalid.

insert

public StringBuffer  insert(int  offset, String  str)

Inserts the string into this string buffer.

The characters of the String argument are inserted, in order, into this string buffer at the indicated offset. The length of the of this string buffer is increased by the length of the argument.

The offset argument must be greater than or equal to 0, and less than or equal to the length (I-§1.17.27) of this string buffer.

Parameters:: offset -the offset; str -a string
Returns:: this string buffer.
Throws: StringIndexOutOfBoundsException (I-§1.44); If the offset is invalid.

length

public int length()

Returns:: the number of characters in this string buffer..

reverses ¹

public StringBuffer reverse()

The character sequence contained in this string buffer is replaced by the reverse of the sequence.

Returns:: this string buffer.

setCharAt

public void  setCharAt(int  index, char  ch)

The character at the specified index of this string buffer is set to ch.

The offset argument must be greater than or equal to 0, and less than the length (I-§1.17.27) of this string buffer.

Parameters:: index -the index of the character to modify; ch -the new character
Throws: StringIndexOutOfBoundsException (I-§1.44); If the index is invalid.

setLength

public void setLength(int  newLength)

If the newLength argument is less than the current length (I-§1.17.27) 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 zero.

Parameters:: newLength -the new length of the buffer
Throws: StringIndexOutOfBoundsException (I-§1.44); If the newLength argument is invalid.

toString

public String toString()

A new 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.

Returns:: a string representation of the string buffer.
Overrides:: toString in class Object (I-§1.12.9).

¹ This method is new in Java 1.1.

Packages  This Package  Prev  Next  Index

§1.17 Class StringBuffer

StringBuffer

StringBuffer

StringBuffer

append

append

append

append

append

append

append

append

append

append

capacity

charAt

ensureCapacity

getChars

insert

insert

insert

insert

insert

insert

insert

insert

insert

length

reverses1

setCharAt

setLength

toString

reverses ¹