StringBuilder

public final class StringBuilder extends Object
implements Appendable CharSequence Serializable CharSequence

A mutable sequence of characters. This class provides an API compatible with StringBuffer, but with no guarantee of synchronization. This class is designed for use as a drop-in replacement for StringBuffer in places where the string buffer was being used by a single thread (as is generally the case). Where possible, it is recommended that this class be used in preference to StringBuffer as it will be faster under most implementations.

The principal operations on a StringBuilder 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 builder. The append method always adds these characters at the end of the builder; the insert method adds the characters at a specified point.

For example, if z refers to a string builder object whose current contents are "start", then the method call z.append("le") would cause the string builder to contain "startle", whereas z.insert(4, "le") would alter the string builder to contain "starlet".

In general, if sb refers to an instance of a StringBuilder, then sb.append(x) has the same effect as sb.insert(sb.length(), x).

Every string builder has a capacity. As long as the length of the character sequence contained in the string builder does not exceed the capacity, it is not necessary to allocate a new internal buffer. If the internal buffer overflows, it is automatically made larger.

Instances of StringBuilder are not safe for use by multiple threads. If such synchronization is required then it is recommended that StringBuffer be used.

Unless otherwise noted, passing a null argument to a constructor or method in this class will cause a NullPointerException to be thrown.

See Also

• StringBuffer
• String

Public Constructor Summary

	StringBuilder() Constructs a string builder with no characters in it and an initial capacity of 16 characters.
	StringBuilder(int capacity) Constructs a string builder with no characters in it and an initial capacity specified by the capacity argument.
	StringBuilder(String str) Constructs a string builder initialized to the contents of the specified string.
	StringBuilder(CharSequence seq) Constructs a string builder that contains the same characters as the specified CharSequence.

Public Method Summary

StringBuilder	append(boolean b)
StringBuilder	append(long lng)
StringBuilder	append(char c) Appends the specified character to this Appendable.
StringBuilder	append(Object obj)
StringBuilder	append(char[] str, int offset, int len)
StringBuilder	append(double d)
StringBuilder	append(char[] str)
StringBuilder	append(String str)
StringBuilder	append(StringBuffer sb) Appends the specified StringBuffer to this sequence.
StringBuilder	append(float f)
StringBuilder	append(int i)
StringBuilder	append(CharSequence s, int start, int end) Appends a subsequence of the specified character sequence to this Appendable.
StringBuilder	append(CharSequence s) Appends the specified character sequence to this Appendable.
StringBuilder	appendCodePoint(int codePoint)
int	capacity()
char	charAt(int i) Returns the char value at the specified index.
int	codePointAt(int i)
int	codePointBefore(int i)
int	codePointCount(int i, int j)
StringBuilder	delete(int start, int end)
StringBuilder	deleteCharAt(int index)
void	ensureCapacity(int i)
void	getChars(int i, int j, char[] buf, int k)
int	indexOf(String s)
int	indexOf(String s, int i)
StringBuilder	insert(int offset, char[] str)
StringBuilder	insert(int offset, float f)
StringBuilder	insert(int dstOffset, CharSequence s)
StringBuilder	insert(int offset, char c)
StringBuilder	insert(int offset, long l)
StringBuilder	insert(int index, char[] str, int offset, int len)
StringBuilder	insert(int offset, int i)
StringBuilder	insert(int offset, String str)
StringBuilder	insert(int offset, double d)
StringBuilder	insert(int dstOffset, CharSequence s, int start, int end)
StringBuilder	insert(int offset, Object obj)
StringBuilder	insert(int offset, boolean b)
int	lastIndexOf(String s, int i)
int	lastIndexOf(String s)
int	length() Returns the length of this character sequence.
int	offsetByCodePoints(int i, int j)
StringBuilder	replace(int start, int end, String str)
StringBuilder	reverse()
void	setCharAt(int i, char c)
void	setLength(int i)
CharSequence	subSequence(int i, int j) Returns a CharSequence that is a subsequence of this sequence.
String	substring(int i, int j)
String	substring(int i)
String	toString() Returns a string containing a concise, human-readable description of this object.
void	trimToSize()

Inherited Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

From interface java.lang.Appendable

abstract Appendable	append(char c) Appends the specified character to this Appendable.
abstract Appendable	append(CharSequence csq, int start, int end) Appends a subsequence of the specified character sequence to this Appendable.
abstract Appendable	append(CharSequence csq) Appends the specified character sequence to this Appendable.

From interface java.lang.CharSequence

abstract char	charAt(int index) Returns the char value at the specified index.
IntStream	chars() Returns a stream of int zero-extending the char values from this sequence.
IntStream	codePoints() Returns a stream of code point values from this sequence.
abstract int	length() Returns the length of this character sequence.
abstract CharSequence	subSequence(int start, int end) Returns a CharSequence that is a subsequence of this sequence.
abstract String	toString() Returns a string containing the characters in this sequence in the same order as this sequence.

Public Constructors

public StringBuilder ()

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

public StringBuilder (int capacity)

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

Parameters

capacity	the initial capacity.

Throws

NegativeArraySizeException	if the capacity argument is less than 0.

public StringBuilder (String str)

Constructs a string builder initialized to the contents of the specified string. The initial capacity of the string builder is 16 plus the length of the string argument.

Parameters

str	the initial contents of the buffer.

public StringBuilder (CharSequence seq)

Constructs a string builder that contains the same characters as the specified CharSequence. The initial capacity of the string builder is 16 plus the length of the CharSequence argument.

Parameters

seq	the sequence to copy.

Public Methods

public StringBuilder append (boolean b)

Parameters

b

public StringBuilder append (long lng)

Parameters

lng

public StringBuilder append (char c)

Appends the specified character to this Appendable.

Parameters

c	The character to append

Returns

• A reference to this Appendable

public StringBuilder append (Object obj)

Parameters

obj

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

Parameters

str
offset
len

Throws

IndexOutOfBoundsException

public StringBuilder append (double d)

Parameters

d

public StringBuilder append (char[] str)

Parameters

str

public StringBuilder append (String str)

Parameters

str

public StringBuilder append (StringBuffer sb)

Appends the specified StringBuffer to this sequence.

The characters of the StringBuffer argument are appended, in order, to this sequence, increasing the length of this sequence by the length of the argument. If sb is null, then the four characters "null" are appended to this sequence.

Let n be the length of this character sequence 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 sb.

Parameters

sb	the StringBuffer to append.

Returns

• a reference to this object.

public StringBuilder append (float f)

Parameters

f

public StringBuilder append (int i)

Parameters

i

public StringBuilder append (CharSequence s, int start, int end)

Appends a subsequence of the specified character sequence to this Appendable.

An invocation of this method of the form out.append(csq, start, end) when csq is not null, behaves in exactly the same way as the invocation

     out.append(csq.subSequence(start, end)) 

Parameters

s	The character sequence from which a subsequence will be appended. If csq is null, then characters will be appended as if csq contained the four characters "null".
start	The index of the first character in the subsequence
end	The index of the character following the last character in the subsequence

Returns

• A reference to this Appendable

Throws

IndexOutOfBoundsException

public StringBuilder append (CharSequence s)

Appends the specified character sequence to this Appendable.

Depending on which class implements the character sequence csq, the entire sequence may not be appended. For instance, if csq is a CharBuffer then the subsequence to append is defined by the buffer's position and limit.

Parameters

s	The character sequence to append. If csq is null, then the four characters "null" are appended to this Appendable.

Returns

• A reference to this Appendable

public StringBuilder appendCodePoint (int codePoint)

Parameters

codePoint

public int capacity ()

public char charAt (int i)

Returns the char value at the specified index. An index ranges from zero to length() - 1. The first char value of the sequence is at index zero, the next at index one, and so on, as for array indexing.

If the char value specified by the index is a surrogate, the surrogate value is returned.

Parameters

i	the index of the char value to be returned

Returns

• the specified char value

public int codePointAt (int i)

Parameters

i

public int codePointBefore (int i)

Parameters

i

public int codePointCount (int i, int j)

Parameters

i
j

public StringBuilder delete (int start, int end)

Parameters

start
end

Throws

StringIndexOutOfBoundsException

public StringBuilder deleteCharAt (int index)

Parameters

index

Throws

StringIndexOutOfBoundsException

public void ensureCapacity (int i)

Parameters

i

public void getChars (int i, int j, char[] buf, int k)

Parameters

i
j
buf
k

public int indexOf (String s)

Parameters

s

public int indexOf (String s, int i)

Parameters

s
i

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

Parameters

offset
str

Throws

StringIndexOutOfBoundsException

public StringBuilder insert (int offset, float f)

Parameters

offset
f

Throws

StringIndexOutOfBoundsException

public StringBuilder insert (int dstOffset, CharSequence s)

Parameters

dstOffset
s

Throws

IndexOutOfBoundsException

public StringBuilder insert (int offset, char c)

Parameters

offset
c

Throws

IndexOutOfBoundsException

public StringBuilder insert (int offset, long l)

Parameters

offset
l

Throws

StringIndexOutOfBoundsException

public StringBuilder insert (int index, char[] str, int offset, int len)

Parameters

index
str
offset
len

Throws

StringIndexOutOfBoundsException

public StringBuilder insert (int offset, int i)

Parameters

offset
i

Throws

StringIndexOutOfBoundsException

public StringBuilder insert (int offset, String str)

Parameters

offset
str

Throws

StringIndexOutOfBoundsException

public StringBuilder insert (int offset, double d)

Parameters

offset
d

Throws

StringIndexOutOfBoundsException

public StringBuilder insert (int dstOffset, CharSequence s, int start, int end)

Parameters

dstOffset
s
start
end

Throws

IndexOutOfBoundsException

public StringBuilder insert (int offset, Object obj)

Parameters

offset
obj

Throws

StringIndexOutOfBoundsException

public StringBuilder insert (int offset, boolean b)

Parameters

offset
b

Throws

StringIndexOutOfBoundsException

public int lastIndexOf (String s, int i)

Parameters

s
i

public int lastIndexOf (String s)

Parameters

s

public int length ()

Returns the length of this character sequence. The length is the number of 16-bit chars in the sequence.

Returns

• the number of chars in this sequence

public int offsetByCodePoints (int i, int j)

Parameters

i
j

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

Parameters

start
end
str

Throws

StringIndexOutOfBoundsException

public StringBuilder reverse ()

public void setCharAt (int i, char c)

Parameters

i
c

public void setLength (int i)

Parameters

i

public CharSequence subSequence (int i, int j)

Returns a CharSequence that is a subsequence of this sequence. The subsequence starts with the char value at the specified index and ends with the char value at index end - 1. The length (in chars) of the returned sequence is end - start, so if start == end then an empty sequence is returned.

Parameters

i	the start index, inclusive
j	the end index, exclusive

Returns

• the specified subsequence

public String substring (int i, int j)

Parameters

i
j

public String substring (int i)

Parameters

i

public String toString ()

Returns a string containing a concise, human-readable description of this object. Subclasses are encouraged to override this method and provide an implementation that takes into account the object's type and data. The default implementation is equivalent to the following expression:

   getClass().getName() + '@' + Integer.toHexString(hashCode())

See Writing a useful toString method if you intend implementing your own toString method.

Returns

• a printable representation of this object.

public void trimToSize ()