Added in API level 1

Summary: Ctors | Methods | Inherited Methods

StringBuffer

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

java.lang.Object
↳	java.lang.StringBuffer

A thread-safe, mutable sequence of characters. A string buffer is like a String, but can be modified. At any point in time it contains some particular sequence of characters, but the length and content of the sequence can be changed through certain method calls.

String buffers are safe for use by multiple threads. The methods are synchronized where necessary so that all the operations on any particular instance behave as if they occur in some serial order that is consistent with the order of the method calls made by each of the individual threads involved.

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

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

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

Whenever an operation occurs involving a source sequence (such as appending or inserting from a source sequence), this class synchronizes only on the string buffer performing the operation, not on the source. Note that while StringBuffer is designed to be safe to use concurrently from multiple threads, if the constructor or the append or insert operation is passed a source sequence that is shared across threads, the calling code must ensure that the operation has a consistent and unchanging view of the source sequence for the duration of the operation. This could be satisfied by the caller holding a lock during the operation's call, by using an immutable source sequence, or by not sharing the source sequence across threads.

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

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

As of release JDK 5, this class has been supplemented with an equivalent class designed for use by a single thread, StringBuilder. The StringBuilder class should generally be used in preference to this one, as it supports all of the same operations but it is faster, as it performs no synchronization.

See also:

StringBuilder
String

Summary

Public constructors
`StringBuffer()` Constructs a string buffer with no characters in it and an initial capacity of 16 characters.
`StringBuffer(int capacity)` Constructs a string buffer with no characters in it and the specified initial capacity.
`StringBuffer(CharSequence seq)` Constructs a string buffer that contains the same characters as the specified `CharSequence`.
`StringBuffer(String str)` Constructs a string buffer initialized to the contents of the specified string.

Public methods
`StringBuffer`	`append(boolean b)`
`StringBuffer`	`append(long lng)`
`StringBuffer`	`append(char c)` Appends the specified character to this `Appendable`.
`StringBuffer`	`append(Object obj)`
`StringBuffer`	`append(char[] str, int offset, int len)`
`StringBuffer`	`append(double d)`
`StringBuffer`	`append(char[] str)`
`StringBuffer`	`append(String str)`
`StringBuffer`	`append(StringBuffer sb)` Appends the specified `StringBuffer` to this sequence.
`StringBuffer`	`append(float f)`
`StringBuffer`	`append(int i)`
`StringBuffer`	`append(CharSequence s, int start, int end)` Appends a subsequence of the specified character sequence to this `Appendable`.
`StringBuffer`	`append(CharSequence s)` Appends the specified `CharSequence` to this sequence.
`StringBuffer`	`appendCodePoint(int codePoint)`
`int`	`capacity()`
`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.
`int`	`codePointAt(int index)`
`int`	`codePointBefore(int index)`
`int`	`codePointCount(int beginIndex, int endIndex)`
`IntStream`	`codePoints()` Returns a stream of code point values from this sequence.
`int`	`compareTo(StringBuffer another)` Compares two `StringBuffer` instances lexicographically.
`StringBuffer`	`delete(int start, int end)`
`StringBuffer`	`deleteCharAt(int index)`
`void`	`ensureCapacity(int minimumCapacity)`
`void`	`getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)`
`int`	`indexOf(String str)`
`int`	`indexOf(String str, int fromIndex)`
`StringBuffer`	`insert(int offset, char[] str)`
`StringBuffer`	`insert(int offset, float f)`
`StringBuffer`	`insert(int dstOffset, CharSequence s)`
`StringBuffer`	`insert(int offset, char c)`
`StringBuffer`	`insert(int offset, long l)`
`StringBuffer`	`insert(int index, char[] str, int offset, int len)`
`StringBuffer`	`insert(int offset, int i)`
`StringBuffer`	`insert(int offset, String str)`
`StringBuffer`	`insert(int offset, double d)`
`StringBuffer`	`insert(int dstOffset, CharSequence s, int start, int end)`
`StringBuffer`	`insert(int offset, boolean b)`
`StringBuffer`	`insert(int offset, Object obj)`
`int`	`lastIndexOf(String str, int fromIndex)`
`int`	`lastIndexOf(String str)`
`int`	`length()` Returns the length of this character sequence.
`int`	`offsetByCodePoints(int index, int codePointOffset)`
`StringBuffer`	`replace(int start, int end, String str)`
`StringBuffer`	`reverse()`
`void`	`setCharAt(int index, char ch)`
`void`	`setLength(int newLength)`
`CharSequence`	`subSequence(int start, int end)` Returns a `CharSequence` that is a subsequence of this sequence.
`String`	`substring(int start, int end)`
`String`	`substring(int start)`
`String`	`toString()` Returns a string representation of the object.
`void`	`trimToSize()`

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 timeoutMillis, int nanos)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait()` Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

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.
`static int`	`compare(CharSequence cs1, CharSequence cs2)` Compares two `CharSequence` instances lexicographically.
`default boolean`	`isEmpty()` Returns `true` if this character sequence is empty.
`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.

From interface


        
          java.lang.Comparable


      compareTo(StringBuffer o)

Compares this object with the specified object for order.

Public constructors

StringBuffer

Added in API level 1

public StringBuffer ()

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

StringBuffer

Added in API level 1

public StringBuffer (int capacity)

Constructs a string buffer with no characters in it and the specified initial capacity.

Parameters
`capacity`	`int`: the initial capacity.

Throws
`NegativeArraySizeException`	if the `capacity` argument is less than `0`.

StringBuffer

Added in API level 1

public StringBuffer (CharSequence seq)

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

If the length of the specified CharSequence is less than or equal to zero, then an empty buffer of capacity 16 is returned.

Parameters
`seq`	`CharSequence`: the sequence to copy.

StringBuffer

Added in API level 1

public StringBuffer (String str)

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

Parameters
`str`	`String`: the initial contents of the buffer.

Public methods

append

Added in API level 1

public StringBuffer append (boolean b)

Parameters
`b`	`boolean`

Returns
`StringBuffer`

append

Added in API level 1

public StringBuffer append (long lng)

Parameters
`lng`	`long`

Returns
`StringBuffer`

append

Added in API level 1

public StringBuffer append (char c)

Appends the specified character to this Appendable.

Parameters
`c`	`char`: The character to append

Returns
`StringBuffer`	A reference to this `Appendable`

append

Added in API level 1

public StringBuffer append (Object obj)

Parameters
`obj`	`Object`

Returns
`StringBuffer`

append

Added in API level 1

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

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

Returns
`StringBuffer`

Throws
`IndexOutOfBoundsException`

append

Added in API level 1

public StringBuffer append (double d)

Parameters
`d`	`double`

Returns
`StringBuffer`

append

Added in API level 1

public StringBuffer append (char[] str)

Parameters
`str`	`char`

Returns
`StringBuffer`

append

Added in API level 1

public StringBuffer append (String str)

Parameters
`str`	`String`

Returns
`StringBuffer`

append

Added in API level 1

public StringBuffer append (StringBuffer sb)

Appends the specified StringBuffer to this sequence.

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

Let n be the length of the old character sequence, the one contained in the StringBuffer 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.

This method synchronizes on this, the destination object, but does not synchronize on the source (sb).

Parameters
`sb`	`StringBuffer`: the `StringBuffer` to append.

Returns
`StringBuffer`	a reference to this object.

append

Added in API level 1

public StringBuffer append (float f)

Parameters
`f`	`float`

Returns
`StringBuffer`

append

Added in API level 1

public StringBuffer append (int i)

Parameters
`i`	`int`

Returns
`StringBuffer`

append

Added in API level 1

public StringBuffer 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
`StringBuffer`	A reference to this `Appendable`

Throws
`IndexOutOfBoundsException`

append

Added in API level 1

public StringBuffer append (CharSequence s)

Appends the specified CharSequence to this sequence.

The characters of the CharSequence argument are appended, in order, increasing the length of this sequence by the length of the argument.

The result of this method is exactly the same as if it were an invocation of this.append(s, 0, s.length());

This method synchronizes on this, the destination object, but does not synchronize on the source (s).

If s is null, then the four characters "null" are appended.

Parameters
`s`	`CharSequence`: the `CharSequence` to append.

Returns
`StringBuffer`	a reference to this object.

appendCodePoint

Added in API level 1

public StringBuffer appendCodePoint (int codePoint)

Parameters
`codePoint`	`int`

Returns
`StringBuffer`

capacity

Added in API level 1

public int capacity ()

Returns
`int`

charAt

Added in API level 1

public char charAt (int index)

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
`index`	`int`: the index of the `char` value to be returned

Returns
`char`	the specified `char` value

Throws
`IndexOutOfBoundsException`

See also:

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)

Parameters
`index`	`int`

Returns
`int`

Throws
`IndexOutOfBoundsException`

codePointBefore

Added in API level 1

public int codePointBefore (int index)

Parameters
`index`	`int`

Returns
`int`

Throws
`IndexOutOfBoundsException`

codePointCount

Added in API level 1

public int codePointCount (int beginIndex, 
                int endIndex)

Parameters
`beginIndex`	`int`
`endIndex`	`int`

Returns
`int`

Throws
`IndexOutOfBoundsException`

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.

Returns
`IntStream`	an IntStream of Unicode code points from this sequence

compareTo

Added in API level 34

public int compareTo (StringBuffer another)

Compares two StringBuffer 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.

Implementation Note:

This method synchronizes on this, the current object, but not StringBuffer another with which this StringBuffer is compared.

Parameters
`another`	`StringBuffer`: the `StringBuffer` to be compared with

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

delete

Added in API level 1

public StringBuffer delete (int start, 
                int end)

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

deleteCharAt

Added in API level 1

public StringBuffer deleteCharAt (int index)

Parameters
`index`	`int`

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

ensureCapacity

Added in API level 1

public void ensureCapacity (int minimumCapacity)

Parameters
`minimumCapacity`	`int`

getChars

Added in API level 1

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

Parameters
`srcBegin`	`int`
`srcEnd`	`int`
`dst`	`char`
`dstBegin`	`int`

Throws
`IndexOutOfBoundsException`

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 StringBuffer insert (int offset, 
                char[] str)

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

insert

Added in API level 1

public StringBuffer insert (int offset, 
                float f)

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

insert

Added in API level 1

public StringBuffer insert (int dstOffset, 
                CharSequence s)

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

Returns
`StringBuffer`

Throws
`IndexOutOfBoundsException`

insert

Added in API level 1

public StringBuffer insert (int offset, 
                char c)

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

Returns
`StringBuffer`

Throws
`IndexOutOfBoundsException`

insert

Added in API level 1

public StringBuffer insert (int offset, 
                long l)

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

insert

Added in API level 1

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

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

insert

Added in API level 1

public StringBuffer insert (int offset, 
                int i)

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

insert

Added in API level 1

public StringBuffer insert (int offset, 
                String str)

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

insert

Added in API level 1

public StringBuffer insert (int offset, 
                double d)

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

insert

Added in API level 1

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

Parameters
`dstOffset`	`int`
`s`	`CharSequence`
`start`	`int`
`end`	`int`

Returns
`StringBuffer`

Throws
`IndexOutOfBoundsException`

insert

Added in API level 1

public StringBuffer insert (int offset, 
                boolean b)

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

insert

Added in API level 1

public StringBuffer insert (int offset, 
                Object obj)

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

Returns
`StringBuffer`

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

Returns
`int`	the number of `char`s in this sequence

offsetByCodePoints

Added in API level 1

public int offsetByCodePoints (int index, 
                int codePointOffset)

Parameters
`index`	`int`
`codePointOffset`	`int`

Returns
`int`

Throws
`IndexOutOfBoundsException`

replace

Added in API level 1

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

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

reverse

Added in API level 1

public StringBuffer reverse ()

Returns
`StringBuffer`

setCharAt

Added in API level 1

public void setCharAt (int index, 
                char ch)

Parameters
`index`	`int`
`ch`	`char`

Throws
`IndexOutOfBoundsException`

See also:

length()

setLength

Added in API level 1

public void setLength (int newLength)

Parameters
`newLength`	`int`

Throws
`IndexOutOfBoundsException`

See also:

length()

subSequence

Added in API level 1

public CharSequence subSequence (int start, 
                int end)

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
`start`	`int`: the start index, inclusive
`end`	`int`: the end index, exclusive

Returns
`CharSequence`	the specified subsequence

Throws
`IndexOutOfBoundsException`

substring

Added in API level 1

public String substring (int start, 
                int end)

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

Returns
`String`

Throws
`StringIndexOutOfBoundsException`

substring

Added in API level 1

public String substring (int start)

Parameters
`start`	`int`

Returns
`String`

Throws
`StringIndexOutOfBoundsException`

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 ()