Added in API level 1

StringBuilder

public final class StringBuilder
extends Object implements Appendable, CharSequence, Serializable, Comparable<StringBuilder>

java.lang.Object
   ↳ java.lang.StringBuilder


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:

Summary

Public constructors

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 methods

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()

Returns the current capacity.

char charAt(int index)

Returns the char value in this sequence at the specified index.

IntStream chars()

Returns a stream of int zero-extending the char values from this sequence.

int codePointAt(int index)

Returns the character (Unicode code point) at the specified index.

int codePointBefore(int index)

Returns the character (Unicode code point) before the specified index.

int codePointCount(int beginIndex, int endIndex)

Returns the number of Unicode code points in the specified text range of this sequence.

IntStream codePoints()

Returns a stream of code point values from this sequence.

int compareTo(StringBuilder another)

Compares two StringBuilder instances lexicographically.

StringBuilder delete(int start, int end)
StringBuilder deleteCharAt(int index)
void ensureCapacity(int minimumCapacity)

Ensures that the capacity is at least equal to the specified minimum.

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

Characters are copied from this sequence into the destination character array dst.

int indexOf(String str)
int indexOf(String str, int fromIndex)
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 str, int fromIndex)
int lastIndexOf(String str)
int length()

Returns the length (character count).

int offsetByCodePoints(int index, int codePointOffset)

Returns the index within this sequence that is offset from the given index by codePointOffset code points.

StringBuilder replace(int start, int end, String str)
StringBuilder reverse()
void setCharAt(int index, char ch)

The character at the specified index is set to ch.

void setLength(int newLength)

Sets the length of the character sequence.

CharSequence subSequence(int start, int end)

Returns a new character sequence that is a subsequence of this sequence.

String substring(int start, int end)

Returns a new String that contains a subsequence of characters currently contained in this sequence.

String substring(int start)

Returns a new String that contains a subsequence of characters currently contained in this character sequence.

String toString()

Returns a string representation of the object.

void trimToSize()

Attempts to reduce storage used for the character sequence.

Inherited methods

Public constructors

StringBuilder

Added in API level 1
public StringBuilder ()

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

StringBuilder

Added in API level 1
public StringBuilder (int capacity)

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

Parameters
capacity int: the initial capacity.

Throws
NegativeArraySizeException if the capacity argument is less than 0.

StringBuilder

Added in API level 1
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 String: the initial contents of the buffer.

StringBuilder

Added in API level 1
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 CharSequence: the sequence to copy.

Public methods

append

Added in API level 1
public StringBuilder append (boolean b)

Parameters
b boolean

Returns
StringBuilder

append

Added in API level 1
public StringBuilder append (long lng)

Parameters
lng long

Returns
StringBuilder

append

Added in API level 1
public StringBuilder append (char c)

Appends the specified character to this Appendable.

Parameters
c char: The character to append

Returns
StringBuilder A reference to this Appendable

append

Added in API level 1
public StringBuilder append (Object obj)

Parameters
obj Object

Returns
StringBuilder

append

Added in API level 1
public StringBuilder append (char[] str, 
                int offset, 
                int len)

Parameters
str char

offset int

len int

Returns
StringBuilder

Throws
IndexOutOfBoundsException

append

Added in API level 1
public StringBuilder append (double d)

Parameters
d double

Returns
StringBuilder

append

Added in API level 1
public StringBuilder append (char[] str)

Parameters
str char

Returns
StringBuilder

append

Added in API level 1
public StringBuilder append (String str)

Parameters
str String

Returns
StringBuilder

append

Added in API level 1
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 StringBuffer: the StringBuffer to append.

Returns
StringBuilder a reference to this object.

append

Added in API level 1
public StringBuilder append (float f)

Parameters
f float

Returns
StringBuilder

append

Added in API level 1
public StringBuilder append (int i)

Parameters
i int

Returns
StringBuilder

append

Added in API level 1
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 CharSequence: 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 int: The index of the first character in the subsequence

end int: The index of the character following the last character in the subsequence

Returns
StringBuilder A reference to this Appendable

Throws
IndexOutOfBoundsException

append

Added in API level 1
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 CharSequence: The character sequence to append. If csq is null, then the four characters "null" are appended to this Appendable.

Returns
StringBuilder A reference to this Appendable

appendCodePoint

Added in API level 1
public StringBuilder appendCodePoint (int codePoint)

Parameters
codePoint int

Returns
StringBuilder

capacity

Added in API level 1
public int capacity ()

Returns the current capacity. The capacity is the amount of storage available for newly inserted characters, beyond which an allocation will occur.

Returns
int the current capacity

charAt

Added in API level 1
public char charAt (int index)

Returns the char value in this sequence at the specified index. The first char value is at index 0, the next at index 1, and so on, as in array indexing.

The index argument must be greater than or equal to 0, and less than the length of this sequence.

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

Parameters
index int: the index of the desired char value.

Returns
char the char value at the specified index.

Throws
IndexOutOfBoundsException if index is negative or greater than or equal to length().

chars

Added in API level 24
public IntStream chars ()

Returns a stream of int zero-extending the char values from this sequence. Any char which maps to a surrogate code point is passed through uninterpreted.

The stream binds to this sequence when the terminal stream operation commences (specifically, for mutable sequences the spliterator for the stream is late-binding). If the sequence is modified during that operation then the result is undefined.

Returns
IntStream an IntStream of char values from this sequence

codePointAt

Added in API level 1
public int codePointAt (int index)

Returns the character (Unicode code point) at the specified index. The index refers to char values (Unicode code units) and ranges from 0 to length()- 1.

If the char value specified at the given index is in the high-surrogate range, the following index is less than the length of this sequence, and the char value at the following index is in the low-surrogate range, then the supplementary code point corresponding to this surrogate pair is returned. Otherwise, the char value at the given index is returned.

Parameters
index int: the index to the char values

Returns
int the code point value of the character at the index

Throws
IndexOutOfBoundsException if the index argument is negative or not less than the length of this sequence.

codePointBefore

Added in API level 1
public int codePointBefore (int index)

Returns the character (Unicode code point) before the specified index. The index refers to char values (Unicode code units) and ranges from 1 to length().

If the char value at (index - 1) is in the low-surrogate range, (index - 2) is not negative, and the char value at (index - 2) is in the high-surrogate range, then the supplementary code point value of the surrogate pair is returned. If the char value at index - 1 is an unpaired low-surrogate or a high-surrogate, the surrogate value is returned.

Parameters
index int: the index following the code point that should be returned

Returns
int the Unicode code point value before the given index.

Throws
IndexOutOfBoundsException if the index argument is less than 1 or greater than the length of this sequence.

codePointCount

Added in API level 1
public int codePointCount (int beginIndex, 
                int endIndex)

Returns the number of Unicode code points in the specified text range of this sequence. The text range begins at the specified beginIndex and extends to the char at index endIndex - 1. Thus the length (in chars) of the text range is endIndex-beginIndex. Unpaired surrogates within this sequence count as one code point each.

Parameters
beginIndex int: the index to the first char of the text range.

endIndex int: the index after the last char of the text range.

Returns
int the number of Unicode code points in the specified text range

Throws
IndexOutOfBoundsException if the beginIndex is negative, or endIndex is larger than the length of this sequence, or beginIndex is larger than endIndex.

codePoints

Added in API level 24
public IntStream codePoints ()

Returns a stream of code point values from this sequence. Any surrogate pairs encountered in the sequence are combined as if by Character.toCodePoint and the result is passed to the stream. Any other code units, including ordinary BMP characters, unpaired surrogates, and undefined code units, are zero-extended to int values which are then passed to the stream.

The stream binds to this sequence when the terminal stream operation commences (specifically, for mutable sequences the spliterator for the stream is late-binding). If the sequence is modified during that operation then the result is undefined.

Returns
IntStream an IntStream of Unicode code points from this sequence

compareTo

Added in API level 34
public int compareTo (StringBuilder another)

Compares two StringBuilder instances lexicographically. This method follows the same rules for lexicographical comparison as defined in the CharSequence.compare(this, another) method.

For finer-grained, locale-sensitive String comparison, refer to Collator.

Parameters
another StringBuilder: the StringBuilder to be compared with

Returns
int the value 0 if this StringBuilder contains the same character sequence as that of the argument StringBuilder; a negative integer if this StringBuilder is lexicographically less than the StringBuilder argument; or a positive integer if this StringBuilder is lexicographically greater than the StringBuilder argument.

delete

Added in API level 1
public StringBuilder delete (int start, 
                int end)

Parameters
start int

end int

Returns
StringBuilder

Throws
StringIndexOutOfBoundsException

deleteCharAt

Added in API level 1
public StringBuilder deleteCharAt (int index)

Parameters
index int

Returns
StringBuilder

Throws
StringIndexOutOfBoundsException

ensureCapacity

Added in API level 1
public void ensureCapacity (int minimumCapacity)

Ensures that the capacity is at least equal to the specified minimum. If the current capacity is less than the argument, then a new internal array 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. Note that subsequent operations on this object can reduce the actual capacity below that requested here.

Parameters
minimumCapacity int: the minimum desired capacity.

getChars

Added in API level 1
public void getChars (int srcBegin, 
                int srcEnd, 
                char[] dst, 
                int dstBegin)

Characters are copied from this sequence 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 int: start copying at this offset.

srcEnd int: stop copying at this offset.

dst char: the array to copy the data into.

dstBegin int: offset into dst.

Throws
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().
  • dstBegin+srcEnd-srcBegin is greater than dst.length

indexOf

Added in API level 1
public int indexOf (String str)

Parameters
str String

Returns
int

indexOf

Added in API level 1
public int indexOf (String str, 
                int fromIndex)

Parameters
str String

fromIndex int

Returns
int

insert

Added in API level 1
public StringBuilder insert (int offset, 
                char[] str)

Parameters
offset int

str char

Returns
StringBuilder

Throws
StringIndexOutOfBoundsException

insert

Added in API level 1
public StringBuilder insert (int offset, 
                float f)

Parameters
offset int

f float

Returns
StringBuilder

Throws
StringIndexOutOfBoundsException

insert

Added in API level 1
public StringBuilder insert (int dstOffset, 
                CharSequence s)

Parameters
dstOffset int

s CharSequence

Returns
StringBuilder

Throws
IndexOutOfBoundsException

insert

Added in API level 1
public StringBuilder insert (int offset, 
                char c)

Parameters
offset int

c char

Returns
StringBuilder

Throws
IndexOutOfBoundsException

insert

Added in API level 1
public StringBuilder insert (int offset, 
                long l)

Parameters
offset int

l long

Returns
StringBuilder

Throws
StringIndexOutOfBoundsException

insert

Added in API level 1
public StringBuilder insert (int index, 
                char[] str, 
                int offset, 
                int len)

Parameters
index int

str char

offset int

len int

Returns
StringBuilder

Throws
StringIndexOutOfBoundsException

insert

Added in API level 1
public StringBuilder insert (int offset, 
                int i)

Parameters
offset int

i int

Returns
StringBuilder

Throws
StringIndexOutOfBoundsException

insert

Added in API level 1
public StringBuilder insert (int offset, 
                String str)

Parameters
offset int

str String

Returns
StringBuilder

Throws
StringIndexOutOfBoundsException

insert

Added in API level 1
public StringBuilder insert (int offset, 
                double d)

Parameters
offset int

d double

Returns
StringBuilder

Throws
StringIndexOutOfBoundsException

insert

Added in API level 1
public StringBuilder insert (int dstOffset, 
                CharSequence s, 
                int start, 
                int end)

Parameters
dstOffset int

s CharSequence

start int

end int

Returns
StringBuilder

Throws
IndexOutOfBoundsException

insert

Added in API level 1
public StringBuilder insert (int offset, 
                Object obj)

Parameters
offset int

obj Object

Returns
StringBuilder

Throws
StringIndexOutOfBoundsException

insert

Added in API level 1
public StringBuilder insert (int offset, 
                boolean b)

Parameters
offset int

b boolean

Returns
StringBuilder

Throws
StringIndexOutOfBoundsException

lastIndexOf

Added in API level 1
public int lastIndexOf (String str, 
                int fromIndex)

Parameters
str String

fromIndex int

Returns
int

lastIndexOf

Added in API level 1
public int lastIndexOf (String str)

Parameters
str String

Returns
int

length

Added in API level 1
public int length ()

Returns the length (character count).

Returns
int the length of the sequence of characters currently represented by this object

offsetByCodePoints

Added in API level 1
public int offsetByCodePoints (int index, 
                int codePointOffset)

Returns the index within this sequence that is offset from the given index by codePointOffset code points. Unpaired surrogates within the text range given by index and codePointOffset count as one code point each.

Parameters
index int: the index to be offset

codePointOffset int: the offset in code points

Returns
int the index within this sequence

Throws
IndexOutOfBoundsException if index is negative or larger then the length of this sequence, or if codePointOffset is positive and the subsequence starting with index has fewer than codePointOffset code points, or if codePointOffset is negative and the subsequence before index has fewer than the absolute value of codePointOffset code points.

replace

Added in API level 1
public StringBuilder replace (int start, 
                int end, 
                String str)

Parameters
start int

end int

str String

Returns
StringBuilder

Throws
StringIndexOutOfBoundsException

reverse

Added in API level 1
public StringBuilder reverse ()

Returns
StringBuilder

setCharAt

Added in API level 1
public void setCharAt (int index, 
                char ch)

The character at the specified index is set to ch. This sequence 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 index argument must be greater than or equal to 0, and less than the length of this sequence.

Parameters
index int: the index of the character to modify.

ch char: the new character.

Throws
IndexOutOfBoundsException if index is negative or greater than or equal to length().

setLength

Added in API level 1
public void setLength (int newLength)

Sets the length of the character sequence. The sequence is changed to 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 '\u0000'. In other words, if the newLength argument is less than the current length, the length is changed to the specified length.

If the newLength argument is greater than or equal to the current length, sufficient null characters ('\u0000') are appended so that length becomes the newLength argument.

The newLength argument must be greater than or equal to 0.

Parameters
newLength int: the new length

Throws
IndexOutOfBoundsException if the newLength argument is negative.

subSequence

Added in API level 1
public CharSequence subSequence (int start, 
                int end)

Returns a new character sequence that is a subsequence of this sequence.

An invocation of this method of the form

sb.subSequence(begin,&nbsp;end)
behaves in exactly the same way as the invocation
sb.substring(begin,&nbsp;end)
This method is provided so that this class can implement the CharSequence interface.

Parameters
start int: the start index, inclusive.

end int: the end index, exclusive.

Returns
CharSequence the specified subsequence.

Throws
IndexOutOfBoundsException if start or end are negative, if end is greater than length(), or if start is greater than end

substring

Added in API level 1
public String substring (int start, 
                int end)

Returns a new String that contains a subsequence of characters currently contained in this sequence. The substring begins at the specified start and extends to the character at index end - 1.

Parameters
start int: The beginning index, inclusive.

end int: The ending index, exclusive.

Returns
String The new string.

Throws
StringIndexOutOfBoundsException if start or end are negative or greater than length(), or start is greater than end.

substring

Added in API level 1
public String substring (int start)

Returns a new String that contains a subsequence of characters currently contained in this character sequence. The substring begins at the specified index and extends to the end of this sequence.

Parameters
start int: The beginning index, inclusive.

Returns
String The new string.

Throws
StringIndexOutOfBoundsException if start is less than zero, or greater than the length of this object.

toString

Added in API level 1
public String toString ()

Returns a string representation of the object.

Returns
String a string representation of the object.

trimToSize

Added in API level 1
public void trimToSize ()

Attempts to reduce storage used for the character sequence. If the buffer is larger than necessary to hold its current sequence of characters, then it may be resized to become more space efficient. Calling this method may, but is not required to, affect the value returned by a subsequent call to the capacity() method.