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java.lang

Class StringBuilder

Implemented Interfaces:
Appendable, CharSequence, Serializable
public final class StringBuilder
extends Object
implements Serializable, CharSequence, Appendable
StringBuilder represents a changeable String. It provides the operations required to modify the StringBuilder, including insert, replace, delete, append, and reverse. It like StringBuffer, but is not synchronized. It is ideal for use when it is known that the object will only be used from a single thread.

StringBuilders 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 StringBuilder 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 StringBuilder operation:
a + b
is the same as
new StringBuilder().append(a).append(b).toString().

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

Since:
1.5
See Also:
String, StringBuffer, Serialized Form

Constructor Summary

StringBuilder()
Create a new StringBuilder with default capacity 16.
StringBuilder(int capacity)
Create an empty StringBuilder with the specified initial capacity.
StringBuilder(CharSequence seq)
Create a new StringBuilder with the characters in the specified CharSequence.
StringBuilder(String str)
Create a new StringBuilder with the characters in the specified String.

Method Summary

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

Methods inherited from class java.lang.Object

clone, equals, extends Object> getClass, finalize, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

StringBuilder

public StringBuilder()
Create a new StringBuilder with default capacity 16.

StringBuilder

public StringBuilder(int capacity)
Create an empty StringBuilder with the specified initial capacity.
Parameters:
capacity - the initial capacity
Throws:
NegativeArraySizeException - if capacity is negative

StringBuilder

public StringBuilder(CharSequence seq)
Create a new StringBuilder with the characters in the specified CharSequence. Initial capacity will be the length of the sequence plus 16; if the sequence reports a length less than or equal to 0, then the initial capacity will be 16.
Parameters:
seq - the initializing CharSequence
Throws:
NullPointerException - if str is null

StringBuilder

public StringBuilder(String str)
Create a new StringBuilder 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 Details

append

public StringBuilder append(boolean bool)
Append the String value of the argument to this StringBuilder. Uses String.valueOf() to convert to String.
Parameters:
bool - the boolean to convert and append
Returns:
this StringBuilder
See Also:
String.valueOf(boolean)

append

public StringBuilder append(char ch)
Append the char to this StringBuilder.
Specified by:
append in interface Appendable
Parameters:
ch - the char to append
Returns:
this StringBuilder

append

public StringBuilder append(char[] data)
Append the char array to this StringBuilder. 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 StringBuilder
Throws:
NullPointerException - if str is null
See Also:
append(char[],int,int)

append

public StringBuilder append(char[] data,
                            int offset,
                            int count)
Append part of the char array to this StringBuilder. 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 StringBuilder
Throws:
NullPointerException - if str is null
IndexOutOfBoundsException - if offset or count is out of range (while unspecified, this is a StringIndexOutOfBoundsException)

append

public StringBuilder append(double dnum)
Append the String value of the argument to this StringBuilder. Uses String.valueOf() to convert to String.
Parameters:
dnum - the double to convert and append
Returns:
this StringBuilder
See Also:
String.valueOf(double)

append

public StringBuilder append(float fnum)
Append the String value of the argument to this StringBuilder. Uses String.valueOf() to convert to String.
Parameters:
fnum - the float to convert and append
Returns:
this StringBuilder
See Also:
String.valueOf(float)

append

public StringBuilder append(int inum)
Append the String value of the argument to this StringBuilder. Uses String.valueOf() to convert to String.
Parameters:
inum - the int to convert and append
Returns:
this StringBuilder
See Also:
String.valueOf(int)

append

public StringBuilder append(CharSequence seq)
Append the characters in the CharSequence to this buffer.
Specified by:
append in interface Appendable
Parameters:
seq - the CharSequence providing the characters
Returns:
this StringBuilder

append

public StringBuilder append(CharSequence seq,
                            int start,
                            int end)
Append some characters from the CharSequence to this buffer. If the argument is null, the four characters "null" are appended.
Specified by:
append in interface Appendable
Parameters:
seq - the CharSequence providing the characters
start - the starting index
end - one past the final index
Returns:
this StringBuilder

append

public StringBuilder append(Object obj)
Append the String value of the argument to this StringBuilder. Uses String.valueOf() to convert to String.
Parameters:
obj - the Object to convert and append
Returns:
this StringBuilder
See Also:
String.valueOf(Object), append(String)

append

public StringBuilder append(String str)
Append the String to this StringBuilder. If str is null, the String "null" is appended.
Parameters:
str - the String to append
Returns:
this StringBuilder

append

public StringBuilder append(StringBuffer stringBuffer)
Append the StringBuilder value of the argument to this StringBuilder. This behaves the same as append((Object) stringBuffer), except it is more efficient.
Parameters:
stringBuffer - the StringBuilder to convert and append
Returns:
this StringBuilder
See Also:
append(Object)

append

public StringBuilder append(long lnum)
Append the String value of the argument to this StringBuilder. Uses String.valueOf() to convert to String.
Parameters:
lnum - the long to convert and append
Returns:
this StringBuilder
See Also:
String.valueOf(long)

appendCodePoint

public StringBuilder appendCodePoint(int code)
Append the code point to this StringBuilder. This is like #append(char), but will append two characters if a supplementary code point is given.
Parameters:
code - the code point to append
Returns:
this StringBuilder
Since:
1.5
See Also:
Character.toChars(int,char[],int)

capacity

public int capacity()
Get the total number of characters this StringBuilder can support before it must be grown. Not to be confused with length.
Returns:
the capacity of this StringBuilder
See Also:
length(), ensureCapacity(int)

charAt

public char charAt(int index)
Get the character at the specified index.
Specified by:
charAt in interface CharSequence
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() (while unspecified, this is a StringIndexOutOfBoundsException)

codePointAt

public int codePointAt(int index)
Get the code point at the specified index. This is like #charAt(int), but if the character is the start of a surrogate pair, and the following character completes the pair, then the corresponding supplementary code point is returned.
Parameters:
index - the index of the codepoint to get, starting at 0
Returns:
the codepoint at the specified index
Throws:
IndexOutOfBoundsException - if index is negative or >= length()
Since:
1.5

codePointBefore

public int codePointBefore(int index)
Get the code point before the specified index. This is like #codePointAt(int), but checks the characters at index-1 and index-2 to see if they form a supplementary code point.
Parameters:
index - the index just past the codepoint to get, starting at 0
Returns:
the codepoint at the specified index
Throws:
IndexOutOfBoundsException - if index is negative or >= length()
Since:
1.5

codePointCount

public int codePointCount(int beginIndex,
                          int endIndex)
Returns the number of Unicode code points in the specified sub sequence. Surrogate pairs count as one code point.
Parameters:
beginIndex - the start of the subarray
endIndex - the index after the last char in the subarray
Returns:
the number of code points
Throws:
IndexOutOfBoundsException - if beginIndex is less than zero or greater than endIndex or if endIndex is greater than the length of this StringBuilder

delete

public StringBuilder delete(int start,
                            int end)
Delete characters from this StringBuilder. 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 StringBuilder
Throws:
StringIndexOutOfBoundsException - if start or end are out of bounds

deleteCharAt

public StringBuilder deleteCharAt(int index)
Delete a character from this StringBuilder.
Parameters:
index - the index of the character to delete
Returns:
this StringBuilder
Throws:
StringIndexOutOfBoundsException - if index is out of bounds

ensureCapacity

public void ensureCapacity(int minimumCapacity)
Increase the capacity of this StringBuilder. 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()

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)

indexOf

public int indexOf(String str)
Finds the first instance of a substring in this StringBuilder.
Parameters:
str - String to find
Returns:
location (base 0) of the String, or -1 if not found
Throws:
NullPointerException - if str is null
See Also:
indexOf(String,int)

indexOf

public int indexOf(String str,
                   int fromIndex)
Finds the first instance of a String in this StringBuilder, 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

insert

public StringBuilder insert(int offset,
                            boolean bool)
Insert the String value of the argument into this StringBuilder. 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 StringBuilder
Throws:
StringIndexOutOfBoundsException - if offset is out of bounds
See Also:
String.valueOf(boolean)

insert

public StringBuilder insert(int offset,
                            char ch)
Insert the char argument into this StringBuilder.
Parameters:
offset - the place to insert in this buffer
ch - the char to insert
Returns:
this StringBuilder
Throws:
StringIndexOutOfBoundsException - if offset is out of bounds

insert

public StringBuilder insert(int offset,
                            char[] data)
Insert the char[] argument into this StringBuilder.
Parameters:
offset - the place to insert in this buffer
data - the char[] to insert
Returns:
this StringBuilder
Throws:
NullPointerException - if data is null
StringIndexOutOfBoundsException - if offset is out of bounds
See Also:
insert(int,char[],int,int)

insert

public StringBuilder insert(int offset,
                            char[] str,
                            int str_offset,
                            int len)
Insert a subarray of the char[] argument into this StringBuilder.
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 StringBuilder
Throws:
NullPointerException - if str is null
StringIndexOutOfBoundsException - if any index is out of bounds

insert

public StringBuilder insert(int offset,
                            double dnum)
Insert the String value of the argument into this StringBuilder. 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 StringBuilder
Throws:
StringIndexOutOfBoundsException - if offset is out of bounds
See Also:
String.valueOf(double)

insert

public StringBuilder insert(int offset,
                            float fnum)
Insert the String value of the argument into this StringBuilder. 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 StringBuilder
Throws:
StringIndexOutOfBoundsException - if offset is out of bounds
See Also:
String.valueOf(float)

insert

public StringBuilder insert(int offset,
                            int inum)
Insert the String value of the argument into this StringBuilder. 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 StringBuilder
Throws:
StringIndexOutOfBoundsException - if offset is out of bounds
See Also:
String.valueOf(int)

insert

public StringBuilder insert(int offset,
                            CharSequence sequence)
Insert the CharSequence argument into this StringBuilder. If the sequence is null, the String "null" is used instead.
Parameters:
offset - the place to insert in this buffer
sequence - the CharSequence to insert
Returns:
this StringBuilder
Throws:
IndexOutOfBoundsException - if offset is out of bounds

insert

public StringBuilder insert(int offset,
                            CharSequence sequence,
                            int start,
                            int end)
Insert a subsequence of the CharSequence argument into this StringBuilder. If the sequence is null, the String "null" is used instead.
Parameters:
offset - the place to insert in this buffer
sequence - the CharSequence to insert
start - the starting index of the subsequence
end - one past the ending index of the subsequence
Returns:
this StringBuilder
Throws:
IndexOutOfBoundsException - if offset, start, or end are out of bounds

insert

public StringBuilder insert(int offset,
                            Object obj)
Insert the String value of the argument into this StringBuilder. 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 StringBuilder
Throws:
StringIndexOutOfBoundsException - if offset is out of bounds
See Also:
String.valueOf(Object)

insert

public StringBuilder insert(int offset,
                            String str)
Insert the String argument into this StringBuilder. 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 StringBuilder
Throws:
StringIndexOutOfBoundsException - if offset is out of bounds

insert

public StringBuilder insert(int offset,
                            long lnum)
Insert the String value of the argument into this StringBuilder. 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 StringBuilder
Throws:
StringIndexOutOfBoundsException - if offset is out of bounds
See Also:
String.valueOf(long)

lastIndexOf

public int lastIndexOf(String str)
Finds the last instance of a substring in this StringBuilder.
Parameters:
str - String to find
Returns:
location (base 0) of the String, or -1 if not found
Throws:
NullPointerException - if str is null
See Also:
lastIndexOf(String,int)

lastIndexOf

public int lastIndexOf(String str,
                       int fromIndex)
Finds the last instance of a String in this StringBuilder, 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

length

public int length()
Get the length of the String this StringBuilder would create. Not to be confused with the capacity of the StringBuilder.
Specified by:
length in interface CharSequence
Returns:
the length of this StringBuilder
See Also:
capacity(), setLength(int)

replace

public StringBuilder 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 StringBuilder, 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 StringBuilder
Throws:
StringIndexOutOfBoundsException - if start or end are out of bounds
NullPointerException - if str is null

reverse

public StringBuilder reverse()
Reverse the characters in this StringBuilder. The same sequence of characters exists, but in the reverse index ordering.
Returns:
this StringBuilder

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)

setLength

public void setLength(int newLength)
Set the length of this StringBuilder. 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()

subSequence

public CharSequence subSequence(int beginIndex,
                                int endIndex)
Creates a substring of this StringBuilder, starting at a specified index and ending at one character before a specified index. This is implemented the same as substring(beginIndex, endIndex), to satisfy the CharSequence interface.
Specified by:
subSequence in interface CharSequence
Parameters:
beginIndex - index to start at (inclusive, base 0)
endIndex - index to end at (exclusive)
Returns:
new String which is a substring of this StringBuilder
Throws:
IndexOutOfBoundsException - if beginIndex or endIndex is out of bounds
See Also:
substring(int,int)

substring

public String substring(int beginIndex)
Creates a substring of this StringBuilder, starting at a specified index and ending at the end of this StringBuilder.
Parameters:
beginIndex - index to start substring (base 0)
Returns:
new String which is a substring of this StringBuilder
Throws:
StringIndexOutOfBoundsException - if beginIndex is out of bounds
See Also:
substring(int,int)

substring

public String substring(int beginIndex,
                        int endIndex)
Creates a substring of this StringBuilder, 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 StringBuilder
Throws:
StringIndexOutOfBoundsException - if beginIndex or endIndex is out of bounds

toString

public String toString()
Convert this StringBuilder to a String. The String is composed of the characters currently in this StringBuilder. Note that the result is a copy, and that future modifications to this buffer do not affect the String.
Specified by:
toString in interface CharSequence
Overrides:
toString in interface Object
Returns:
the characters in this StringBuilder

trimToSize

public void trimToSize()
StringBuilder.java -- Unsynchronized growable strings Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005 Free Software Foundation, Inc. This file is part of GNU Classpath. GNU Classpath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Classpath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Classpath; see the file COPYING. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination. As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.

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