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Summary: Ctors | Methods | Inherited Methods

StringBuffer

public final class StringBuffer
extends Object implements Appendable, CharSequence, 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(String str)` Constructs a string buffer initialized to the contents of the specified string.
`StringBuffer(CharSequence seq)` Constructs a string buffer that contains the same characters as the specified `CharSequence`.

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.
`int`	`codePointAt(int index)`
`int`	`codePointBefore(int index)`
`int`	`codePointCount(int beginIndex, int endIndex)`
`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, Object obj)`
`StringBuffer`	`insert(int offset, boolean b)`
`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 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

StringBuffer

public StringBuffer ()

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

StringBuffer

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

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.

StringBuffer

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.

Public methods

append

public StringBuffer append (boolean b)

Parameters
`b`	`boolean`

Returns
`StringBuffer`

append

public StringBuffer append (long lng)

Parameters
`lng`	`long`

Returns
`StringBuffer`

append

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

public StringBuffer append (Object obj)

Parameters
`obj`	`Object`

Returns
`StringBuffer`

append

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

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

Returns
`StringBuffer`

Throws
`IndexOutOfBoundsException`

append

public StringBuffer append (double d)

Parameters
`d`	`double`

Returns
`StringBuffer`

append

public StringBuffer append (char[] str)

Parameters
`str`	`char`

Returns
`StringBuffer`

append

public StringBuffer append (String str)

Parameters
`str`	`String`

Returns
`StringBuffer`

append

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

public StringBuffer append (float f)

Parameters
`f`	`float`

Returns
`StringBuffer`

append

public StringBuffer append (int i)

Parameters
`i`	`int`

Returns
`StringBuffer`

append

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

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

public StringBuffer appendCodePoint (int codePoint)

Parameters
`codePoint`	`int`

Returns
`StringBuffer`

capacity

public int capacity ()

Returns
`int`

charAt

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()

codePointAt

public int codePointAt (int index)

Parameters
`index`	`int`

Returns
`int`

codePointBefore

public int codePointBefore (int index)

Parameters
`index`	`int`

Returns
`int`

codePointCount

public int codePointCount (int beginIndex, 
                int endIndex)

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

Returns
`int`

delete

public StringBuffer delete (int start, 
                int end)

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

deleteCharAt

public StringBuffer deleteCharAt (int index)

Parameters
`index`	`int`

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

ensureCapacity

public void ensureCapacity (int minimumCapacity)

Parameters
`minimumCapacity`	`int`

getChars

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

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

Throws
`IndexOutOfBoundsException`

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 StringBuffer insert (int offset, 
                char[] str)

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

insert

public StringBuffer insert (int offset, 
                float f)

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

insert

public StringBuffer insert (int dstOffset, 
                CharSequence s)

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

Returns
`StringBuffer`

Throws
`IndexOutOfBoundsException`

insert

public StringBuffer insert (int offset, 
                char c)

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

Returns
`StringBuffer`

Throws
`IndexOutOfBoundsException`

insert

public StringBuffer insert (int offset, 
                long l)

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

insert

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

public StringBuffer insert (int offset, 
                int i)

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

insert

public StringBuffer insert (int offset, 
                String str)

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

insert

public StringBuffer insert (int offset, 
                double d)

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

insert

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

public StringBuffer insert (int offset, 
                Object obj)

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

insert

public StringBuffer insert (int offset, 
                boolean b)

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

Returns
`StringBuffer`

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 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

public int offsetByCodePoints (int index, 
                int codePointOffset)

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

Returns
`int`

replace

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

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

Returns
`StringBuffer`

Throws
`StringIndexOutOfBoundsException`

reverse

public StringBuffer reverse ()

Returns
`StringBuffer`

setCharAt

public void setCharAt (int index, 
                char ch)

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

Throws
`IndexOutOfBoundsException`

See also:

length()

setLength

public void setLength (int newLength)

Parameters
`newLength`	`int`

Throws
`IndexOutOfBoundsException`

See also:

length()

subSequence

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

public String substring (int start, 
                int end)

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

Returns
`String`

Throws
`StringIndexOutOfBoundsException`

substring

public String substring (int start)

Parameters
`start`	`int`

Returns
`String`

Throws
`StringIndexOutOfBoundsException`

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 ()