StringBuilder

java.lang.Object
- java.lang.StringBuilder

所有已实现的接口:

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

从以下版本开始:

1.5

另请参阅:

StringBuffer, String, 序列化表格

构造器概要

构造器
构造器	说明
`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(CharSequence seq)`	Constructs a string builder that contains the same characters as the specified `CharSequence`.
`StringBuilder(String str)`	Constructs a string builder 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
`StringBuilder`	`append(boolean b)`
`StringBuilder`	`append(char c)`	Appends the specified character to this `Appendable`.
`StringBuilder`	`append(char[] str)`
`StringBuilder`	`append(char[] str, int offset, int len)`
`StringBuilder`	`append(double d)`
`StringBuilder`	`append(float f)`
`StringBuilder`	`append(int i)`
`StringBuilder`	`append(long lng)`
`StringBuilder`	`append(CharSequence s)`	Appends the specified character sequence to this `Appendable`.
`StringBuilder`	`append(CharSequence s, int start, int end)`	Appends a subsequence of the specified character sequence to this `Appendable`.
`StringBuilder`	`append(Object obj)`
`StringBuilder`	`append(String str)`
`StringBuilder`	`append(StringBuffer sb)`	Appends the specified `StringBuffer` to this sequence.
`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, boolean b)`
`StringBuilder`	`insert(int offset, char c)`
`StringBuilder`	`insert(int offset, char[] str)`
`StringBuilder`	`insert(int index, char[] str, int offset, int len)`
`StringBuilder`	`insert(int offset, double d)`
`StringBuilder`	`insert(int offset, float f)`
`StringBuilder`	`insert(int offset, int i)`
`StringBuilder`	`insert(int offset, long l)`
`StringBuilder`	`insert(int dstOffset, CharSequence s)`
`StringBuilder`	`insert(int dstOffset, CharSequence s, int start, int end)`
`StringBuilder`	`insert(int offset, Object obj)`
`StringBuilder`	`insert(int offset, String str)`
`int`	`lastIndexOf(String str)`
`int`	`lastIndexOf(String str, int fromIndex)`
`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)`	Returns a new `String` that contains a subsequence of characters currently contained in this character sequence.
`String`	`substring(int start, int end)`	Returns a new `String` that contains a subsequence of characters currently contained in this sequence.
`String`	`toString()`	Returns a string representation of the object.
`void`	`trimToSize()`	Attempts to reduce storage used for the character sequence.

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
  - 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.
    
    参数:
    
    capacity - the initial capacity.
    
    抛出:
    
    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.
    
    参数:
    
    str - 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.
    
    参数:
    
    seq - the sequence to copy.
- 方法详细资料
  - append
```
public StringBuilder append(Object obj)
```
  - append
```
public StringBuilder append(String str)
```
  - 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.
    
    参数:
    
    sb - the StringBuffer to append.
    
    返回:
    
    a reference to this object.
  - append
```
public StringBuilder append(CharSequence s)
```
    从接口复制的说明: Appendable
    
    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.
    
    指定者:
    
    append 在接口中 Appendable
    
    参数:
    
    s - The character sequence to append. If csq is null, then the four characters "null" are appended to this Appendable.
    
    返回:
    
    A reference to this Appendable
  - append
```
public StringBuilder 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()
  - append
```
public StringBuilder append(char[] str)
```
  - append
```
public StringBuilder append(char[] str,
                            int offset,
                            int len)
```
    抛出:
    
    IndexOutOfBoundsException
  - append
```
public StringBuilder append(boolean b)
```
  - append
```
public StringBuilder 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 StringBuilder append(int i)
```
  - append
```
public StringBuilder append(long lng)
```
  - append
```
public StringBuilder append(float f)
```
  - append
```
public StringBuilder append(double d)
```
  - appendCodePoint
```
public StringBuilder appendCodePoint(int codePoint)
```
    从以下版本开始:
    
    1.5
  - delete
```
public StringBuilder delete(int start,
                            int end)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - deleteCharAt
```
public StringBuilder deleteCharAt(int index)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - replace
```
public StringBuilder replace(int start,
                             int end,
                             String str)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - insert
```
public StringBuilder insert(int index,
                            char[] str,
                            int offset,
                            int len)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - insert
```
public StringBuilder insert(int offset,
                            Object obj)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - insert
```
public StringBuilder insert(int offset,
                            String str)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - insert
```
public StringBuilder insert(int offset,
                            char[] str)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - insert
```
public StringBuilder insert(int dstOffset,
                            CharSequence s)
```
    抛出:
    
    IndexOutOfBoundsException
  - insert
```
public StringBuilder insert(int dstOffset,
                            CharSequence s,
                            int start,
                            int end)
```
    抛出:
    
    IndexOutOfBoundsException
  - insert
```
public StringBuilder insert(int offset,
                            boolean b)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - insert
```
public StringBuilder insert(int offset,
                            char c)
```
    抛出:
    
    IndexOutOfBoundsException
  - insert
```
public StringBuilder insert(int offset,
                            int i)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - insert
```
public StringBuilder insert(int offset,
                            long l)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - insert
```
public StringBuilder insert(int offset,
                            float f)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - insert
```
public StringBuilder insert(int offset,
                            double d)
```
    抛出:
    
    StringIndexOutOfBoundsException
  - indexOf
```
public int indexOf(String str)
```
  - indexOf
```
public int indexOf(String str,
                   int fromIndex)
```
  - lastIndexOf
```
public int lastIndexOf(String str)
```
  - lastIndexOf
```
public int lastIndexOf(String str,
                       int fromIndex)
```
  - reverse
```
public StringBuilder reverse()
```
  - 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.
  - 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.
  - 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.
    
    参数:
    
    index - the index to the char values
    
    返回:
    
    the code point value of the character at the index
    
    抛出:
    
    IndexOutOfBoundsException - if the index argument is negative or not less than the length of this sequence.
  - 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
 
```
    参数:
    
    srcBegin - start copying at this offset.
    
    srcEnd - stop copying at this offset.
    
    dst - the array to copy the data into.
    
    dstBegin - offset into dst.
    
    抛出:
    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
  - length
```
public int length()
```
    Returns the length (character count).
    
    指定者:
    
    length 在接口中 CharSequence
    
    返回:
    
    the length of the sequence of characters currently represented by this object
  - 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.
    
    参数:
    
    index - the index of the character to modify.
    
    ch - the new character.
    
    抛出:
    
    IndexOutOfBoundsException - if index is negative or greater than or equal to length().
  - 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.
    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
  - 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.
    
    参数:
    
    start - The beginning index, inclusive.
    
    返回:
    
    The new string.
    
    抛出:
    
    StringIndexOutOfBoundsException - if start is less than zero, or greater than the length of this object.
  - 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.
    
    参数:
    
    start - The beginning index, inclusive.
    
    end - The ending index, exclusive.
    
    返回:
    
    The new string.
    
    抛出:
    
    StringIndexOutOfBoundsException - if start or end are negative or greater than length(), or start is greater than end.
  - 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.
    
    返回:
    
    the current capacity
  - 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.
    
    参数:
    
    newLength - the new length
    
    抛出:
    
    IndexOutOfBoundsException - if the newLength argument is negative.
  - 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.
    参数:
    
    minimumCapacity - the minimum desired capacity.
  - 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.
    
    参数:
    
    index - the index following the code point that should be returned
    
    返回:
    
    the Unicode code point value before the given index.
    
    抛出:
    
    IndexOutOfBoundsException - if the index argument is less than 1 or greater than the length of this sequence.
  - 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.
    
    指定者:
    
    charAt 在接口中 CharSequence
    
    参数:
    
    index - the index of the desired char value.
    
    返回:
    
    the char value at the specified index.
    
    抛出:
    
    IndexOutOfBoundsException - if index is negative or greater than or equal to length().
  - 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.
    
    参数:
    
    beginIndex - the index to the first char of the text range.
    
    endIndex - the index after the last char of the text range.
    
    返回:
    
    the number of Unicode code points in the specified text range
    
    抛出:
    
    IndexOutOfBoundsException - if the beginIndex is negative, or endIndex is larger than the length of this sequence, or beginIndex is larger than endIndex.
  - 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.
    
    参数:
    
    index - the index to be offset
    
    codePointOffset - the offset in code points
    
    返回:
    
    the index within this sequence
    
    抛出:
    
    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.

类 StringBuilder

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

StringBuilder

StringBuilder

StringBuilder

StringBuilder

方法详细资料

append

append

append

append

append

append

append

append

append

append

append

append

append

appendCodePoint

delete

deleteCharAt

replace

insert

insert

insert

insert

insert

insert

insert

insert

insert

insert

insert

insert

indexOf

indexOf

lastIndexOf

lastIndexOf

reverse

toString

trimToSize

codePointAt

getChars

length

setCharAt

subSequence

substring

substring

capacity

setLength

ensureCapacity

codePointBefore

charAt

codePointCount

offsetByCodePoints