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Summary: Ctors | Methods | Inherited Methods

StringBuilder

public final class StringBuilder
extends Object implements Appendable, CharSequence, Serializable

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:

StringBuffer
String

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.
`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.
`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

From class


        
          java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the object.
`final void`	`notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()` Returns a string representation of the object.
`final void`	`wait(long timeout, int nanos)` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.
`final void`	`wait(long timeout)` Causes the current thread to wait until either another thread invokes the `notify()` method or the `notifyAll()` method for this object, or a specified amount of time has elapsed.
`final void`	`wait()` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for 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.
`default IntStream`	`chars()` Returns a stream of `int` zero-extending the `char` values from this sequence.
`default 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

StringBuilder

public StringBuilder ()

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

StringBuilder

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

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

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

public StringBuilder append (boolean b)

Parameters
`b`	`boolean`

Returns
`StringBuilder`

append

public StringBuilder append (long lng)

Parameters
`lng`	`long`

Returns
`StringBuilder`

append

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

public StringBuilder append (Object obj)

Parameters
`obj`	`Object`

Returns
`StringBuilder`

append

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

Parameters
`str`	`char`
`offset`	`int`
`len`	`int`

Returns
`StringBuilder`

Throws
`IndexOutOfBoundsException`

append

public StringBuilder append (double d)

Parameters
`d`	`double`

Returns
`StringBuilder`

append

public StringBuilder append (char[] str)

Parameters
`str`	`char`

Returns
`StringBuilder`

append

public StringBuilder append (String str)

Parameters
`str`	`String`

Returns
`StringBuilder`

append

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

public StringBuilder append (float f)

Parameters
`f`	`float`

Returns
`StringBuilder`

append

public StringBuilder append (int i)

Parameters
`i`	`int`

Returns
`StringBuilder`

append

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

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

public StringBuilder appendCodePoint (int codePoint)

Parameters
`codePoint`	`int`

Returns
`StringBuilder`

capacity

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

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()`.

codePointAt

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

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

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`.

delete

public StringBuilder delete (int start, 
                int end)

Parameters
`start`	`int`
`end`	`int`

Returns
`StringBuilder`

Throws
`StringIndexOutOfBoundsException`

deleteCharAt

public StringBuilder deleteCharAt (int index)

Parameters
`index`	`int`

Returns
`StringBuilder`

Throws
`StringIndexOutOfBoundsException`

ensureCapacity

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

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

public int indexOf (String str)

Parameters
`str`	`String`

Returns
`int`

indexOf

public int indexOf (String str, 
                int fromIndex)

Parameters
`str`	`String`
`fromIndex`	`int`

Returns
`int`

insert

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

Parameters
`offset`	`int`
`str`	`char`

Returns
`StringBuilder`

Throws
`StringIndexOutOfBoundsException`

insert

public StringBuilder insert (int offset, 
                float f)

Parameters
`offset`	`int`
`f`	`float`

Returns
`StringBuilder`

Throws
`StringIndexOutOfBoundsException`

insert

public StringBuilder insert (int dstOffset, 
                CharSequence s)

Parameters
`dstOffset`	`int`
`s`	`CharSequence`

Returns
`StringBuilder`

Throws
`IndexOutOfBoundsException`

insert

public StringBuilder insert (int offset, 
                char c)

Parameters
`offset`	`int`
`c`	`char`

Returns
`StringBuilder`

Throws
`IndexOutOfBoundsException`

insert

public StringBuilder insert (int offset, 
                long l)

Parameters
`offset`	`int`
`l`	`long`

Returns
`StringBuilder`

Throws
`StringIndexOutOfBoundsException`

insert

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

public StringBuilder insert (int offset, 
                int i)

Parameters
`offset`	`int`
`i`	`int`

Returns
`StringBuilder`

Throws
`StringIndexOutOfBoundsException`

insert

public StringBuilder insert (int offset, 
                String str)

Parameters
`offset`	`int`
`str`	`String`

Returns
`StringBuilder`

Throws
`StringIndexOutOfBoundsException`

insert

public StringBuilder insert (int offset, 
                double d)

Parameters
`offset`	`int`
`d`	`double`

Returns
`StringBuilder`

Throws
`StringIndexOutOfBoundsException`

insert

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

public StringBuilder insert (int offset, 
                Object obj)

Parameters
`offset`	`int`
`obj`	`Object`

Returns
`StringBuilder`

Throws
`StringIndexOutOfBoundsException`

insert

public StringBuilder insert (int offset, 
                boolean b)

Parameters
`offset`	`int`
`b`	`boolean`

Returns
`StringBuilder`

Throws
`StringIndexOutOfBoundsException`

lastIndexOf

public int lastIndexOf (String str, 
                int fromIndex)

Parameters
`str`	`String`
`fromIndex`	`int`

Returns
`int`

lastIndexOf

public int lastIndexOf (String str)

Parameters
`str`	`String`

Returns
`int`

length

public int length ()

Returns the length (character count).

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

offsetByCodePoints

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

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

Parameters
`start`	`int`
`end`	`int`
`str`	`String`

Returns
`StringBuilder`

Throws
`StringIndexOutOfBoundsException`

reverse

public StringBuilder reverse ()

Returns
`StringBuilder`

setCharAt

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

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

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

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

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

public String toString ()

Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

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

Returns
`String`	a string representation of the object.

trimToSize

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.