StringBuffer

java.lang.Object
- java.lang.StringBuffer

所有已实现的接口:

Serializable, Appendable, CharSequence
```
public final class StringBuffer
extends Object
implements Appendable, CharSequence, Serializable
```
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.

从以下版本开始:

JDK1.0

另请参阅:

StringBuilder, String, 序列化表格

构造器概要

构造器
构造器	说明
`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.

方法概要

所有方法实例方法具体方法
限定符和类型	方法	说明
`StringBuffer`	`append(boolean b)`
`StringBuffer`	`append(char c)`	Appends the specified character to this `Appendable`.
`StringBuffer`	`append(char[] str)`
`StringBuffer`	`append(char[] str, int offset, int len)`
`StringBuffer`	`append(double d)`
`StringBuffer`	`append(float f)`
`StringBuffer`	`append(int i)`
`StringBuffer`	`append(long lng)`
`StringBuffer`	`append(CharSequence s)`	Appends the specified `CharSequence` to this sequence.
`StringBuffer`	`append(CharSequence s, int start, int end)`	Appends a subsequence of the specified character sequence to this `Appendable`.
`StringBuffer`	`append(Object obj)`
`StringBuffer`	`append(String str)`
`StringBuffer`	`append(StringBuffer sb)`	Appends the specified `StringBuffer` 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, boolean b)`
`StringBuffer`	`insert(int offset, char c)`
`StringBuffer`	`insert(int offset, char[] str)`
`StringBuffer`	`insert(int index, char[] str, int offset, int len)`
`StringBuffer`	`insert(int offset, double d)`
`StringBuffer`	`insert(int offset, float f)`
`StringBuffer`	`insert(int offset, int i)`
`StringBuffer`	`insert(int offset, long l)`
`StringBuffer`	`insert(int dstOffset, CharSequence s)`
`StringBuffer`	`insert(int dstOffset, CharSequence s, int start, int end)`
`StringBuffer`	`insert(int offset, Object obj)`
`StringBuffer`	`insert(int offset, String str)`
`int`	`lastIndexOf(String str)`
`int`	`lastIndexOf(String str, int fromIndex)`
`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)`
`String`	`substring(int start, int end)`
`String`	`toString()`	Returns a string representation of the object.
`void`	`trimToSize()`

从接口继承的方法 java.lang.CharSequence
chars, codePoints

从类继承的方法 java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

- 构造器详细资料
  - 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.
    
    参数:
    
    capacity - the initial capacity.
    
    抛出:
    
    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.
    
    参数:
    
    str - 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.
    
    参数:
    
    seq - the sequence to copy.
    
    从以下版本开始:
    
    1.5
- 方法详细资料
  - length
```
public int length()
```
    从接口复制的说明: CharSequence
    
    Returns the length of this character sequence. The length is the number of 16-bit chars in the sequence.
    
    指定者:
    
    length 在接口中 CharSequence
    
    返回:
    
    the number of chars in this sequence
  - capacity
```
public int capacity()
```
  - ensureCapacity
```
public void ensureCapacity(int minimumCapacity)
```
  - trimToSize
```
public void trimToSize()
```
    从以下版本开始:
    
    1.5
  - setLength
```
public void setLength(int newLength)
```
    抛出:
    
    IndexOutOfBoundsException
    
    另请参阅:
    
    length()
  - charAt
```
public char charAt(int index)
```
    从接口复制的说明: CharSequence
    
    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.
    
    指定者:
    
    charAt 在接口中 CharSequence
    
    参数:
    
    index - the index of the char value to be returned
    
    返回:
    
    the specified char value
    
    抛出:
    
    IndexOutOfBoundsException - if the index argument is negative or not less than length()
    
    另请参阅:
    
    length()
  - codePointAt
```
public int codePointAt(int index)
```
    从以下版本开始:
    
    1.5
  - codePointBefore
```
public int codePointBefore(int index)
```
    从以下版本开始:
    
    1.5
  - codePointCount
```
public int codePointCount(int beginIndex,
                          int endIndex)
```
    从以下版本开始:
    
    1.5
  - offsetByCodePoints
```
public int offsetByCodePoints(int index,
                              int codePointOffset)
```
    从以下版本开始:
    
    1.5
  - getChars
```
public void getChars(int srcBegin,
                     int srcEnd,
                     char[] dst,
                     int dstBegin)
```
    抛出:
    
    IndexOutOfBoundsException
  - setCharAt
```
public void setCharAt(int index,
                      char ch)
```
    抛出:
    
    IndexOutOfBoundsException
    
    另请参阅:
    
    length()
  - append
```
public StringBuffer append(Object obj)
```
  - append
```
public StringBuffer append(String str)
```
  - 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).
    
    参数:
    
    sb - the StringBuffer to append.
    
    返回:
    
    a reference to this object.
    
    从以下版本开始:
    
    1.4
  - 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.
    
    指定者:
    
    append 在接口中 Appendable
    
    参数:
    
    s - the CharSequence to append.
    
    返回:
    
    a reference to this object.
    
    从以下版本开始:
    
    1.5
  - append
```
public StringBuffer append(CharSequence s,
                           int start,
                           int end)
```
    从接口复制的说明: Appendable
    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)) 
```
    指定者:
    
    append 在接口中 Appendable
    
    参数:
    
    s - The character sequence from which a subsequence will be appended. If csq is null, then characters will be appended as if csq contained the four characters "null".
    
    start - The index of the first character in the subsequence
    
    end - The index of the character following the last character in the subsequence
    
    返回:
    
    A reference to this Appendable
    
    抛出:
    
    IndexOutOfBoundsException - If start or end are negative, start is greater than end, or end is greater than csq.length()
    
    从以下版本开始:
    
    1.5
  - append
```
public StringBuffer append(char[] str)
```
  - append
```
public StringBuffer append(char[] str,
                           int offset,
                           int len)
```
    抛出:
    
    IndexOutOfBoundsException
  - append
```
public StringBuffer append(boolean b)
```
  - append
```
public StringBuffer append(char c)
```
    从接口复制的说明: Appendable
    
    Appends the specified character to this Appendable.
    
    指定者:
    
    append 在接口中 Appendable
    
    参数:
    
    c - The character to append
    
    返回:
    
    A reference to this Appendable
  - append
```
public StringBuffer append(int i)
```
  - appendCodePoint
```
public StringBuffer appendCodePoint(int codePoint)
```
    从以下版本开始:
    
    1.5
  - append
```
public StringBuffer append(long lng)
```
  - append
```
public StringBuffer append(float f)
```
  - append
```
public StringBuffer append(double d)
```
  - delete
```
public StringBuffer delete(int start,
                           int end)
```
    抛出:
    
    StringIndexOutOfBoundsException
    
    从以下版本开始:
    
    1.2
  - deleteCharAt
```
public StringBuffer deleteCharAt(int index)
```
    抛出:
    
    StringIndexOutOfBoundsException
    
    从以下版本开始:
    
    1.2
  - replace
```
public StringBuffer replace(int start,
                            int end,
                            String str)
```
    抛出:
    
    StringIndexOutOfBoundsException
    
    从以下版本开始:
    
    1.2
  - substring
```
public String substring(int start)
```
    抛出:
    
    StringIndexOutOfBoundsException
    
    从以下版本开始:
    
    1.2
  - subSequence
```
public CharSequence subSequence(int start,
                                int end)
```
    从接口复制的说明: CharSequence
    
    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.
    
    指定者:
    
    subSequence 在接口中 CharSequence
    
    参数:
    
    start - the start index, inclusive
    
    end - the end index, exclusive
    
    返回:
    
    the specified subsequence
    
    抛出:
    
    IndexOutOfBoundsException - if start or end are negative, if end is greater than length(), or if start is greater than end
    
    从以下版本开始:
    
    1.4
  - substring
```
public String substring(int start,
                        int end)
```
    抛出:
    
    StringIndexOutOfBoundsException
    
    从以下版本开始:
    
    1.2
  - insert
```
public StringBuffer insert(int index,
                           char[] str,
                           int offset,
                           int len)
```
    抛出:
    
    StringIndexOutOfBoundsException
    
    从以下版本开始:
    
    1.2
  - insert
```
public StringBuffer insert(int offset,
                           Object obj)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - insert
```
public StringBuffer insert(int offset,
                           String str)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - insert
```
public StringBuffer insert(int offset,
                           char[] str)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - insert
```
public StringBuffer insert(int dstOffset,
                           CharSequence s)
```
    抛出:
    
    IndexOutOfBoundsException
    
    从以下版本开始:
    
    1.5
  - insert
```
public StringBuffer insert(int dstOffset,
                           CharSequence s,
                           int start,
                           int end)
```
    抛出:
    
    IndexOutOfBoundsException
    
    从以下版本开始:
    
    1.5
  - insert
```
public StringBuffer insert(int offset,
                           boolean b)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - insert
```
public StringBuffer insert(int offset,
                           char c)
```
    抛出:
    
    IndexOutOfBoundsException
  - insert
```
public StringBuffer insert(int offset,
                           int i)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - insert
```
public StringBuffer insert(int offset,
                           long l)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - insert
```
public StringBuffer insert(int offset,
                           float f)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - insert
```
public StringBuffer insert(int offset,
                           double d)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - indexOf
```
public int indexOf(String str)
```
    从以下版本开始:
    
    1.4
  - indexOf
```
public int indexOf(String str,
                   int fromIndex)
```
    从以下版本开始:
    
    1.4
  - lastIndexOf
```
public int lastIndexOf(String str)
```
    从以下版本开始:
    
    1.4
  - lastIndexOf
```
public int lastIndexOf(String str,
                       int fromIndex)
```
    从以下版本开始:
    
    1.4
  - reverse
```
public StringBuffer reverse()
```
    从以下版本开始:
    
    JDK1.0.2
  - toString
```
public String toString()
```
    从类复制的说明: Object
    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())
    指定者:
    
    toString 在接口中 CharSequence
    
    覆盖:
    
    toString 在类中 Object
    
    返回:
    
    a string representation of the object.

类 StringBuffer

构造器概要

方法概要

从接口继承的方法 java.lang.CharSequence

从类继承的方法 java.lang.Object

构造器详细资料

StringBuffer

StringBuffer

StringBuffer

StringBuffer

方法详细资料

length

capacity

ensureCapacity

trimToSize

setLength

charAt

codePointAt

codePointBefore

codePointCount

offsetByCodePoints

getChars

setCharAt

append

append

append

append

append

append

append

append

append

append

appendCodePoint

append

append

append

delete

deleteCharAt

replace

substring

subSequence

substring

insert

insert

insert

insert

insert

insert

insert

insert

insert

insert

insert

insert

indexOf

indexOf

lastIndexOf

lastIndexOf

reverse

toString