java.lang StringBuffer

java.lang
StringBuffer

Declaration
public final class StringBuffer
java.lang.Object
|
+--java.lang.StringBuffer
Description
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:
x = new StringBuffer().append(“a”).append(4).append(“c”)
.toString()
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.
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.

Constructors
StringBuffer()
StringBuffer(int length)
StringBuffer(String str)
Methods
StringBuffer append(boolean b)
StringBuffer append(char c)
StringBuffer append(char[] str)
StringBuffer append(char[] str, int offset, int len)
StringBuffer append(double d)
StringBuffer append(float f)
StringBuffer append(int i)
StringBuffer append(long l)
StringBuffer append(Object obj)
StringBuffer append(String str)
int capacity()
char charAt(int index)
StringBuffer delete(int start, int end)
StringBuffer deleteCharAt(int index)
void ensureCapacity(int minimumCapacity)
void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
StringBuffer insert(int offset, boolean b)
StringBuffer insert(int offset, char c)
StringBuffer insert(int offset, char[] str)
StringBuffer insert(int offset, double d)
StringBuffer insert(int offset, float f)
StringBuffer insert(int offset, int i)
StringBuffer insert(int offset, long l)
StringBuffer insert(int offset, Object obj)
StringBuffer insert(int offset, String str)
int length()
StringBuffer reverse()
void setCharAt(int index, char ch)
void setLength(int newLength)
String toString()



Methods inherited from class Object
equals(Object), getClass(), hashCode(), notify(), notifyAll(), wait(), wait(), wait()



Constructors
StringBuffer()
Declaration:
public StringBuffer()
Description:
Constructs a string buffer with no characters in it and an initial capacity of 16 characters.
StringBuffer(int)
Declaration:
public StringBuffer(int length)
Description:
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 - if the length argument is less than 0.
StringBuffer(String)
Declaration:
public StringBuffer(java.lang.String str)
Description:
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. The initial capacity of
the string buffer is 16 plus the length of the string argument.
Parameters:
str - the initial contents of the buffer.
Methods
length()
Declaration:
public int length()
Description:
Returns the length (character count) of this string buffer.
Returns: the length of the sequence of characters currently represented by this string buffer.
capacity()
Declaration:
public int capacity()



Description:
Returns the current capacity of the String buffer. The capacity is the amount of storage available for newly
inserted characters; beyond which an allocation will occur.
Returns: the current capacity of this string buffer.
ensureCapacity(int)
Declaration:
public void ensureCapacity(int minimumCapacity)
Description:
Ensures that the capacity of the buffer is at least equal to the specified minimum. 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.
setLength(int)
Declaration:
public void setLength(int newLength)
Description:
Sets the length of this string buffer. This string buffer is altered to represent a new character sequence whose
length is specified by the argument. For every nonnegative index k less than 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.
Parameters:
newLength - the new length of the buffer.
Throws:
IndexOutOfBoundsException - if the newLength argument is negative.
See Also: length()
charAt(int)
Declaration:
public char charAt(int index)



getChars(int, int, char[], int)
224
Description:
The specified character of the sequence currently represented by the string buffer, as indicated by the
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.
Parameters:
index - the index of the desired character.
Returns: the character at the specified index of this string buffer.
Throws:
IndexOutOfBoundsException - if index is negative or greater than or equal to length().
See Also: length()
getChars(int, int, char[], int)
Declaration:
public void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
Description:
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 - 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.
Throws:
NullPointerException - if dst is null.
IndexOutOfBoundsException - if any of the following is true:
• srcBegin is negative
• dstBegin is negative
• the 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
setCharAt(int, char)
Declaration:
public void setCharAt(int index, char ch)

Description:
The character at the specified index of this string buffer is set to 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.
Parameters:
index - the index of the character to modify.
ch - the new character.
Throws:
IndexOutOfBoundsException - if index is negative or greater than or equal to length().
See Also: length()
append(Object)
Declaration:
public java.lang.StringBuffer append(java.lang.Object obj)
Description:
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, and the characters of that
string are then appended to this string buffer.
Parameters:
obj - an Object.
Returns: a reference to this StringBuffer object.
See Also: String.valueOf(Object), append(String)
append(String)
Declaration:
public java.lang.StringBuffer append(java.lang.String str)
Description:
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. 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.
Parameters:
str - a string.
Returns: a reference to this StringBuffer.
append(char[])
Declaration:
public java.lang.StringBuffer append(char[] str)



append(char[], int, int)

Description:
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.
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.
Parameters:
str - the characters to be appended.
Returns: a reference to this StringBuffer object.
append(char[], int, int)
Declaration:
public java.lang.StringBuffer append(char[] str, int offset, int len)
Description:
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.
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.
Parameters:
str - the characters to be appended.
offset - the index of the first character to append.
len - the number of characters to append.
Returns: a reference to this StringBuffer object.
append(boolean)
Declaration:
public java.lang.StringBuffer append(boolean b)
Description:
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, and the characters of that
string are then appended to this string buffer.
Parameters:
b - a boolean.
Returns: a reference to this StringBuffer.
See Also: String.valueOf(boolean), append(String)
append(char)
Declaration:
public java.lang.StringBuffer append(char c)



Description:
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
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.
Parameters:
c - a char.
Returns: a reference to this StringBuffer object.
append(int)
Declaration:
public java.lang.StringBuffer append(int i)
Description:
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, and the characters of that
string are then appended to this string buffer.
Parameters:
i - an int.
Returns: a reference to this StringBuffer object.
See Also: String.valueOf(int), append(String)
append(long)
Declaration:
public java.lang.StringBuffer append(long l)
Description:
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, and the characters of that
string are then appended to this string buffer.
Parameters:
l - a long.
Returns: a reference to this StringBuffer object.
See Also: String.valueOf(long), append(String)
append(float)
Declaration:
public java.lang.StringBuffer append(float f)
Description:
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, and the characters of that
string are then appended to this string buffer.