java.lang
Class StringBuffer

java.lang.Object
  java.lang.StringBuffer

public final class StringBuffer
extends Object

StringBuffer represents a changeable String. It provides the operations required to modify the StringBuffer, including insert, replace, delete, append, and reverse. It is thread-safe; meaning that all modifications to a buffer are in synchronized methods.

StringBuffers are variable-length in nature, so even if you initialize them to a certain size, they can still grow larger than that. Capacity indicates the number of characters the StringBuffer can have in it before it has to grow (growing the char array is an expensive operation involving new).

Incidentally, compilers often implement the String operator "+" by using a StringBuffer operation:
a + b
is the same as
new StringBuffer().append(a).append(b).toString().

Classpath's StringBuffer is capable of sharing memory with Strings for efficiency. This will help when a StringBuffer is converted to a String and the StringBuffer is not changed after that (quite common when performing string concatenation).

Since:

1.0

See Also:

String

Constructor Summary

StringBuffer()
Create a new StringBuffer with default capacity 16.

StringBuffer(int capacity)
Create an empty StringBuffer with the specified initial capacity.

StringBuffer(String str)
Create a new StringBuffer with the characters in the specified String.

Method Summary

StringBuffer	append(boolean bool) Append the String value of the argument to this StringBuffer.
StringBuffer	append(char ch) Append the char to this StringBuffer.
StringBuffer	append(char[] data) Append the char array to this StringBuffer.
StringBuffer	append(char[] data, int offset, int count) Append part of the char array to this StringBuffer.
StringBuffer	append(double dnum) Append the String value of the argument to this StringBuffer.
StringBuffer	append(float fnum) Append the String value of the argument to this StringBuffer.
StringBuffer	append(int inum) Append the String value of the argument to this StringBuffer.
StringBuffer	append(long lnum) Append the String value of the argument to this StringBuffer.
StringBuffer	append(Object obj) Append the String value of the argument to this StringBuffer.
StringBuffer	append(String str) Append the String to this StringBuffer.
StringBuffer	append(StringBuffer stringBuffer) Append the StringBuffer value of the argument to this StringBuffer.
int	capacity() Get the total number of characters this StringBuffer can support before it must be grown.
char	charAt(int index) Get the character at the specified index.
StringBuffer	delete(int start, int end) Delete characters from this StringBuffer.
StringBuffer	deleteCharAt(int index) Delete a character from this StringBuffer.
void	ensureCapacity(int minimumCapacity) Increase the capacity of this StringBuffer.
void	getChars(int srcOffset, int srcEnd, char[] dst, int dstOffset) Get the specified array of characters.
int	indexOf(String str) Finds the first instance of a substring in this StringBuffer.
int	indexOf(String str, int fromIndex) Finds the first instance of a String in this StringBuffer, starting at a given index.
StringBuffer	insert(int offset, boolean bool) Insert the String value of the argument into this StringBuffer.
StringBuffer	insert(int offset, char ch) Insert the char argument into this StringBuffer.
StringBuffer	insert(int offset, char[] data) Insert the char[] argument into this StringBuffer.
StringBuffer	insert(int offset, char[] str, int str_offset, int len) Insert a subarray of the char[] argument into this StringBuffer.
StringBuffer	insert(int offset, double dnum) Insert the String value of the argument into this StringBuffer.
StringBuffer	insert(int offset, float fnum) Insert the String value of the argument into this StringBuffer.
StringBuffer	insert(int offset, int inum) Insert the String value of the argument into this StringBuffer.
StringBuffer	insert(int offset, long lnum) Insert the String value of the argument into this StringBuffer.
StringBuffer	insert(int offset, Object obj) Insert the String value of the argument into this StringBuffer.
StringBuffer	insert(int offset, String str) Insert the String argument into this StringBuffer.
int	lastIndexOf(String str) Finds the last instance of a substring in this StringBuffer.
int	lastIndexOf(String str, int fromIndex) Finds the last instance of a String in this StringBuffer, starting at a given index.
int	length() Get the length of the String this StringBuffer would create.
StringBuffer	replace(int start, int end, String str) Replace characters between index start (inclusive) and end (exclusive) with str.
StringBuffer	reverse() Reverse the characters in this StringBuffer.
void	setCharAt(int index, char ch) Set the character at the specified index.
void	setLength(int newLength) Set the length of this StringBuffer.
String	substring(int beginIndex) Creates a substring of this StringBuffer, starting at a specified index and ending at the end of this StringBuffer.
String	substring(int beginIndex, int endIndex) Creates a substring of this StringBuffer, starting at a specified index and ending at one character before a specified index.
String	toString() Convert this StringBuffer to a String.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

StringBuffer

public StringBuffer()

Create a new StringBuffer with default capacity 16.

StringBuffer

public StringBuffer(int capacity)

Create an empty StringBuffer with the specified initial capacity.

Parameters:

capacity - the initial capacity

Throws:

NegativeArraySizeException - if capacity is negative

StringBuffer

public StringBuffer(String str)

Create a new StringBuffer with the characters in the specified String. Initial capacity will be the size of the String plus 16.

Parameters:

str - the String to convert

Throws:

NullPointerException - if str is null

Method Detail

length

public int length()

Get the length of the String this StringBuffer would create. Not to be confused with the capacity of the StringBuffer.

Returns:

the length of this StringBuffer

See Also:

capacity(), setLength(int)

capacity

public int capacity()

Get the total number of characters this StringBuffer can support before it must be grown. Not to be confused with length.

Returns:

the capacity of this StringBuffer

See Also:

length(), ensureCapacity(int)

ensureCapacity

public void ensureCapacity(int minimumCapacity)

Increase the capacity of this StringBuffer. This will ensure that an expensive growing operation will not occur until minimumCapacity is reached. The buffer is grown to the larger of minimumCapacity and capacity() * 2 + 2, if it is not already large enough.

Parameters:

minimumCapacity - the new capacity

See Also:

capacity()

setLength

public void setLength(int newLength)

Set the length of this StringBuffer. If the new length is greater than the current length, all the new characters are set to '\0'. If the new length is less than the current length, the first newLength characters of the old array will be preserved, and the remaining characters are truncated.

Parameters:

newLength - the new length

Throws:

IndexOutOfBoundsException - if the new length is negative (while unspecified, this is a StringIndexOutOfBoundsException)

See Also:

length()

charAt

public char charAt(int index)

Get the character at the specified index.

Parameters:

index - the index of the character to get, starting at 0

Returns:

the character at the specified index

Throws:

IndexOutOfBoundsException - if index is negative or >= length()

getChars

public void getChars(int srcOffset,
                     int srcEnd,
                     char[] dst,
                     int dstOffset)

Get the specified array of characters. srcOffset - srcEnd characters will be copied into the array you pass in.

Parameters:

srcOffset - the index to start copying from (inclusive)

srcEnd - the index to stop copying from (exclusive)

dst - the array to copy into

dstOffset - the index to start copying into

Throws:

NullPointerException - if dst is null

IndexOutOfBoundsException - if any source or target indices are out of range (while unspecified, source problems cause a StringIndexOutOfBoundsException, and dest problems cause an ArrayIndexOutOfBoundsException)

See Also:

System.arraycopy(Object, int, Object, int, int)

setCharAt

public void setCharAt(int index,
                      char ch)

Set the character at the specified index.

Parameters:

index - the index of the character to set starting at 0

ch - the value to set that character to

Throws:

IndexOutOfBoundsException - if index is negative or >= length() (while unspecified, this is a StringIndexOutOfBoundsException)

append

public StringBuffer append(Object obj)

Append the String value of the argument to this StringBuffer. Uses String.valueOf() to convert to String.

Parameters:

obj - the Object to convert and append

Returns:

this StringBuffer

See Also:

String.valueOf(Object), append(String)

append

public StringBuffer append(String str)

Append the String to this StringBuffer. If str is null, the String "null" is appended.

Parameters:

str - the String to append

Returns:

this StringBuffer

append

public StringBuffer append(StringBuffer stringBuffer)

Append the StringBuffer value of the argument to this StringBuffer. This behaves the same as append((Object) stringBuffer), except it is more efficient.

Parameters:

stringBuffer - the StringBuffer to convert and append

Returns:

this StringBuffer

Since:

1.4

See Also:

append(Object)

append

public StringBuffer append(char[] data)

Append the char array to this StringBuffer. This is similar (but more efficient) than append(new String(data)), except in the case of null.

Parameters:

data - the char[] to append

Returns:

this StringBuffer

Throws:

NullPointerException - if str is null

See Also:

append(char[], int, int)

append

public StringBuffer append(char[] data,
                           int offset,
                           int count)

Append part of the char array to this StringBuffer. This is similar (but more efficient) than append(new String(data, offset, count)), except in the case of null.

Parameters:

data - the char[] to append

offset - the start location in str

count - the number of characters to get from str

Returns:

this StringBuffer

Throws:

NullPointerException - if str is null

IndexOutOfBoundsException - if offset or count is out of range (while unspecified, this is a StringIndexOutOfBoundsException)

append

public StringBuffer append(boolean bool)

Append the String value of the argument to this StringBuffer. Uses String.valueOf() to convert to String.

Parameters:

bool - the boolean to convert and append

Returns:

this StringBuffer

See Also:

String.valueOf(boolean)

append

public StringBuffer append(char ch)

Append the char to this StringBuffer.

Parameters:

ch - the char to append

Returns:

this StringBuffer

append

public StringBuffer append(int inum)

Append the String value of the argument to this StringBuffer. Uses String.valueOf() to convert to String.

Parameters:

inum - the int to convert and append

Returns:

this StringBuffer

See Also:

String.valueOf(int)

append

public StringBuffer append(long lnum)

Append the String value of the argument to this StringBuffer. Uses String.valueOf() to convert to String.

Parameters:

lnum - the long to convert and append

Returns:

this StringBuffer

See Also:

String.valueOf(long)

append

public StringBuffer append(float fnum)

Append the String value of the argument to this StringBuffer. Uses String.valueOf() to convert to String.

Parameters:

fnum - the float to convert and append

Returns:

this StringBuffer

See Also:

String.valueOf(float)

append

public StringBuffer append(double dnum)

Append the String value of the argument to this StringBuffer. Uses String.valueOf() to convert to String.

Parameters:

dnum - the double to convert and append

Returns:

this StringBuffer

See Also:

String.valueOf(double)

delete

public StringBuffer delete(int start,
                           int end)

Delete characters from this StringBuffer. delete(10, 12) will delete 10 and 11, but not 12. It is harmless for end to be larger than length().

Parameters:

start - the first character to delete

end - the index after the last character to delete

Returns:

this StringBuffer

Throws:

StringIndexOutOfBoundsException - if start or end are out of bounds

Since:

1.2

deleteCharAt

public StringBuffer deleteCharAt(int index)

Delete a character from this StringBuffer.

Parameters:

index - the index of the character to delete

Returns:

this StringBuffer

Throws:

StringIndexOutOfBoundsException - if index is out of bounds

Since:

1.2

replace

public StringBuffer replace(int start,
                            int end,
                            String str)

Replace characters between index start (inclusive) and end (exclusive) with str. If end is larger than the size of this StringBuffer, all characters after start are replaced.

Parameters:

start - the beginning index of characters to delete (inclusive)

end - the ending index of characters to delete (exclusive)

str - the new String to insert

Returns:

this StringBuffer

Throws:

StringIndexOutOfBoundsException - if start or end are out of bounds

NullPointerException - if str is null

Since:

1.2

substring

public String substring(int beginIndex)

Creates a substring of this StringBuffer, starting at a specified index and ending at the end of this StringBuffer.

Parameters:

beginIndex - index to start substring (base 0)

Returns:

new String which is a substring of this StringBuffer

Throws:

StringIndexOutOfBoundsException - if beginIndex is out of bounds

Since:

1.2

See Also:

substring(int, int)

substring

public String substring(int beginIndex,
                        int endIndex)

Creates a substring of this StringBuffer, starting at a specified index and ending at one character before a specified index.

Parameters:

beginIndex - index to start at (inclusive, base 0)

endIndex - index to end at (exclusive)

Returns:

new String which is a substring of this StringBuffer

Throws:

StringIndexOutOfBoundsException - if beginIndex or endIndex is out of bounds

Since:

1.2

insert

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

Insert a subarray of the char[] argument into this StringBuffer.

Parameters:

offset - the place to insert in this buffer

str - the char[] to insert

str_offset - the index in str to start inserting from

len - the number of characters to insert

Returns:

this StringBuffer

Throws:

NullPointerException - if str is null

StringIndexOutOfBoundsException - if any index is out of bounds

Since:

1.2

insert

public StringBuffer insert(int offset,
                           Object obj)

Insert the String value of the argument into this StringBuffer. Uses String.valueOf() to convert to String.

Parameters:

offset - the place to insert in this buffer

obj - the Object to convert and insert

Returns:

this StringBuffer

Throws:

StringIndexOutOfBoundsException - if offset is out of bounds

See Also:

String.valueOf(Object)

insert

public StringBuffer insert(int offset,
                           String str)

Insert the String argument into this StringBuffer. If str is null, the String "null" is used instead.

Parameters:

offset - the place to insert in this buffer

str - the String to insert

Returns:

this StringBuffer

Throws:

StringIndexOutOfBoundsException - if offset is out of bounds

insert

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

Insert the char[] argument into this StringBuffer.

Parameters:

offset - the place to insert in this buffer

data - the char[] to insert

Returns:

this StringBuffer

Throws:

NullPointerException - if data is null

StringIndexOutOfBoundsException - if offset is out of bounds

See Also:

insert(int, char[], int, int)

insert

public StringBuffer insert(int offset,
                           boolean bool)

Insert the String value of the argument into this StringBuffer. Uses String.valueOf() to convert to String.

Parameters:

offset - the place to insert in this buffer

bool - the boolean to convert and insert

Returns:

this StringBuffer

Throws:

StringIndexOutOfBoundsException - if offset is out of bounds

See Also:

String.valueOf(boolean)

insert

public StringBuffer insert(int offset,
                           char ch)

Insert the char argument into this StringBuffer.

Parameters:

offset - the place to insert in this buffer

ch - the char to insert

Returns:

this StringBuffer

Throws:

StringIndexOutOfBoundsException - if offset is out of bounds

insert

public StringBuffer insert(int offset,
                           int inum)

Insert the String value of the argument into this StringBuffer. Uses String.valueOf() to convert to String.

Parameters:

offset - the place to insert in this buffer

inum - the int to convert and insert

Returns:

this StringBuffer

Throws:

StringIndexOutOfBoundsException - if offset is out of bounds

See Also:

String.valueOf(int)

insert

public StringBuffer insert(int offset,
                           long lnum)

Insert the String value of the argument into this StringBuffer. Uses String.valueOf() to convert to String.

Parameters:

offset - the place to insert in this buffer

lnum - the long to convert and insert

Returns:

this StringBuffer

Throws:

StringIndexOutOfBoundsException - if offset is out of bounds

See Also:

String.valueOf(long)

insert

public StringBuffer insert(int offset,
                           float fnum)

Insert the String value of the argument into this StringBuffer. Uses String.valueOf() to convert to String.

Parameters:

offset - the place to insert in this buffer

fnum - the float to convert and insert

Returns:

this StringBuffer

Throws:

StringIndexOutOfBoundsException - if offset is out of bounds

See Also:

String.valueOf(float)

insert

public StringBuffer insert(int offset,
                           double dnum)

Insert the String value of the argument into this StringBuffer. Uses String.valueOf() to convert to String.

Parameters:

offset - the place to insert in this buffer

dnum - the double to convert and insert

Returns:

this StringBuffer

Throws:

StringIndexOutOfBoundsException - if offset is out of bounds

See Also:

String.valueOf(double)

indexOf

public int indexOf(String str)

Finds the first instance of a substring in this StringBuffer.

Parameters:

str - String to find

Returns:

location (base 0) of the String, or -1 if not found

Throws:

NullPointerException - if str is null

Since:

1.4

See Also:

indexOf(String, int)

indexOf

public int indexOf(String str,
                   int fromIndex)

Finds the first instance of a String in this StringBuffer, starting at a given index. If starting index is less than 0, the search starts at the beginning of this String. If the starting index is greater than the length of this String, or the substring is not found, -1 is returned.

Parameters:

str - String to find

fromIndex - index to start the search

Returns:

location (base 0) of the String, or -1 if not found

Throws:

NullPointerException - if str is null

Since:

1.4

lastIndexOf

public int lastIndexOf(String str)

Finds the last instance of a substring in this StringBuffer.

Parameters:

str - String to find

Returns:

location (base 0) of the String, or -1 if not found

Throws:

NullPointerException - if str is null

Since:

1.4

See Also:

lastIndexOf(String, int)

lastIndexOf

public int lastIndexOf(String str,
                       int fromIndex)

Finds the last instance of a String in this StringBuffer, starting at a given index. If starting index is greater than the maximum valid index, then the search begins at the end of this String. If the starting index is less than zero, or the substring is not found, -1 is returned.

Parameters:

str - String to find

fromIndex - index to start the search

Returns:

location (base 0) of the String, or -1 if not found

Throws:

NullPointerException - if str is null

Since:

1.4

reverse

public StringBuffer reverse()

Reverse the characters in this StringBuffer. The same sequence of characters exists, but in the reverse index ordering.

Returns:

this StringBuffer

toString

public String toString()

Convert this StringBuffer to a String. The String is composed of the characters currently in this StringBuffer. Note that the result is a copy, and that future modifications to this buffer do not affect the String.

Overrides:

toString in class Object

Returns:

the characters in this StringBuffer

See Also:

Object.getClass(), Object.hashCode(), Class.getName(), Integer.toHexString(int)