java.lang
类 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 Serializable, CharSequence

线程安全的可变字符序列。一个类似于 String 的字符串缓冲区，但不能修改。虽然在任意时间点上它都包含某种特定的字符序列，但通过某些方法调用可以改变该序列的长度和内容。

可将字符串缓冲区安全地用于多个线程。可以在必要时对这些方法进行同步，因此任意特定实例上的所有操作就好像是以串行顺序发生的，该顺序与所涉及的每个线程进行的方法调用顺序一致。

StringBuffer 上的主要操作是 append 和 insert 方法，可重载这些方法，以接受任意类型的数据。每个方法都能有效地将给定的数据转换成字符串，然后将该字符串的字符添加或插入到字符串缓冲区中。append 方法始终将这些字符添加到缓冲区的末端；而 insert 方法则在指定的点添加字符。

例如，如果 z 引用一个当前内容是“start”的字符串缓冲区对象，则此方法调用 z.append("le") 会使字符串缓冲区包含“startle”，而 z.insert(4, "le") 将更改字符串缓冲区，使之包含“starlet”。

通常，如果 sb 引用 StringBuilder 的一个实例，则 sb.append(x) 和 sb.insert(sb.length(), x) 具有相同的效果。

只要发生有关源序列（如在源序列中添加或插入）的操作，该类就只在执行此操作的字符串缓冲区上而不是在源上实现同步。

每个字符串缓冲区都有一定的容量。只要字符串缓冲区所包含的字符序列的长度没有超出此容量，就无需分配新的内部缓冲区数组。如果内部缓冲区溢出，则此容量自动增大。从 JDK 5 开始，为该类补充了一个单个线程使用的等价类，即 StringBuilder。与该类相比，通常应该优先使用 StringBuilder 类，因为它支持所有相同的操作，但由于它不执行同步，所以速度更快。

从以下版本开始：

JDK1.0

另请参见：

StringBuilder, String, 序列化表格

StringBuffer

public StringBuffer()

构造一个其中不带字符的字符串缓冲区，初始容量为 16 个字符。

StringBuffer

public StringBuffer(int capacity)

构造一个不带字符，但具有指定初始容量的字符串缓冲区。

参数：

capacity - 初始容量。

抛出：

NegativeArraySizeException - 如果 capacity 参数小于 0。

StringBuffer

public StringBuffer(String str)

构造一个字符串缓冲区，并将其内容初始化为指定的字符串内容。该字符串的初始容量为 16 加上字符串参数的长度。

参数：

str - 缓冲区的初始内容。

抛出：

NullPointerException - 如果 str 为 null

StringBuffer

public StringBuffer(CharSequence seq)

public java.lang.StringBuilder(CharSequence seq) 构造一个字符串缓冲区，它包含与指定的 CharSequence 相同的字符。该字符串缓冲区的初始容量为 16 加上 CharSequence 参数的长度。

如果指定的 CharSequence 的长度小于或等于 0，则返回容量为 16 的空缓冲区。

参数：

seq - 要复制的序列。

抛出：

NullPointerException - 如果 seq 为 null

从以下版本开始：

1.5

length

public int length()

Returns the length (character count).

指定者：

接口 CharSequence 中的 length

返回：

the length of the sequence of characters currently represented by this object

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

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.

参数：

minimumCapacity - the minimum desired capacity.

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.

从以下版本开始：

1.5

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.

另请参见：

length()

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：

接口 CharSequence 中的 charAt

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().

另请参见：

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.

参数：

index - the index to the char values

返回：

the code point value of the character at the index

从以下版本开始：

1.5

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.

从以下版本开始：

1.5

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

从以下版本开始：

1.5

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

从以下版本开始：

1.5

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：

NullPointerException - if dst is null.

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

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().

另请参见：

length()

append

public StringBuffer append(Object obj)

Appends the string representation of the Object argument.

The argument is converted to a string as if by the method String.valueOf, and the characters of that string are then appended to this sequence.

参数：

obj - an Object.

返回：

a reference to this object.

另请参见：

String.valueOf(java.lang.Object), append(java.lang.String)

append

public StringBuffer append(String str)

Appends the specified string to this character sequence.

The characters of the String argument are appended, in order, increasing the length of this sequence by the length of the argument. If str is null, then the four characters "null" are appended.

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 str.

参数：

str - a string.

返回：

a reference to this object.

append

public StringBuffer append(StringBuffer sb)

将指定的 StringBuffer 添加到此序列中。

按顺序将 StringBuffer 参数中的字符添加到此 StringBuffer 中，并使 StringBuffer 在长度上增加该参数的长度。如果 sb 为 null，则将 4 个 "null" 字符添加到此 StringBuffer 中。

在执行 append 方法前，让 StringBuffer 中包含的原有字符序列的长度为 n。如果 k 小于 n，则新字符序列中索引 k 处的字符等于原有字符序列中索引 k 处的字符；否则它等于参数 sb 中索引 k-n 处的字符。

该方法在 this（目标）对象上实现同步，但不在源上（sb）实现同步。

参数：

sb - 要添加的 StringBuffer。

返回：

该对象的一个引用。

从以下版本开始：

1.4

append

public StringBuffer append(CharSequence s)

将指定的 CharSequence 添加到该序列。

按顺序将 CharSequence 参数中的字符添加到该序列中，使该序列增加该参数的长度。

该方法的结果与调用 this.append(s, 0, s.length()) 完全相同；

该方法在 this（目标）对象上实现同步，但不在源上（s）实现同步。

如果 s 为 null，则添加 4 个 "null" 字符。

指定者：

接口 Appendable 中的 append

参数：

s - 要添加的 CharSequence。

返回：

此对象的一个引用。

从以下版本开始：

1.5

append

public StringBuffer append(CharSequence s,
                           int start,
                           int end)

Appends a subsequence of the specified CharSequence to this sequence.

Characters of the argument s, starting at index start, are appended, in order, to the contents of this sequence up to the (exclusive) index end. The length of this sequence is increased by the value of end - start.

Let n be the length of this character sequence just prior to execution of the append method. Then the character at index k in this character sequence becomes equal to the character at index k in this sequence, if k is less than n; otherwise, it is equal to the character at index k+start-n in the argument s.

If s is null, then this method appends characters as if the s parameter was a sequence containing the four characters "null".

指定者：

接口 Appendable 中的 append

参数：

s - the sequence to append.

start - the starting index of the subsequence to be appended.

end - the end index of the subsequence to be appended.

返回：

a reference to this object.

抛出：

IndexOutOfBoundsException - if start or end are negative, or start is greater than end or end is greater than s.length()

从以下版本开始：

1.5

append

public StringBuffer append(char[] str)

Appends the string representation of the char array argument to this sequence.

The characters of the array argument are appended, in order, to the contents of this sequence. The length of this sequence increases by the length of the argument.

The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(char[]) and the characters of that string were then appended to this character sequence.

参数：

str - the characters to be appended.

返回：

a reference to this object.

append

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

Appends the string representation of a subarray of the char array argument to this sequence.

Characters of the char array str, starting at index offset, are appended, in order, to the contents of this sequence. The length of this sequence increases by the value of len.

The overall effect is exactly as if the arguments were converted to a string by the method String.valueOf(char[],int,int) and the characters of that string were then appended to this character sequence.

参数：

str - the characters to be appended.

offset - the index of the first char to append.

len - the number of chars to append.

返回：

a reference to this object.

append

public StringBuffer append(boolean b)

Appends the string representation of the boolean argument to the sequence.

The argument is converted to a string as if by the method String.valueOf, and the characters of that string are then appended to this sequence.

参数：

b - a boolean.

返回：

a reference to this object.

另请参见：

String.valueOf(boolean), append(java.lang.String)

append

public StringBuffer append(char c)

Appends the string representation of the char argument to this sequence.

The argument is appended to the contents of this sequence. The length of this sequence increases by 1.

The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(char) and the character in that string were then appended to this character sequence.

指定者：

接口 Appendable 中的 append

参数：

c - a char.

返回：

a reference to this object.

append

public StringBuffer append(int i)

Appends the string representation of the int argument to this sequence.

The argument is converted to a string as if by the method String.valueOf, and the characters of that string are then appended to this sequence.

参数：

i - an int.

返回：

a reference to this object.

另请参见：

String.valueOf(int), append(java.lang.String)

appendCodePoint

public StringBuffer appendCodePoint(int codePoint)

Appends the string representation of the codePoint argument to this sequence.

The argument is appended to the contents of this sequence. The length of this sequence increases by Character.charCount(codePoint).

The overall effect is exactly as if the argument were converted to a char array by the method Character.toChars(int) and the character in that array were then appended to this character sequence.

参数：

codePoint - a Unicode code point

返回：

a reference to this object.

从以下版本开始：

1.5

append

public StringBuffer append(long lng)

Appends the string representation of the long argument to this sequence.

The argument is converted to a string as if by the method String.valueOf, and the characters of that string are then appended to this sequence.

参数：

lng - a long.

返回：

a reference to this object.

另请参见：

String.valueOf(long), append(java.lang.String)

append

public StringBuffer append(float f)

Appends the string representation of the float argument to this sequence.

The argument is converted to a string as if by the method String.valueOf, and the characters of that string are then appended to this string sequence.

参数：

f - a float.

返回：

a reference to this object.

另请参见：

String.valueOf(float), append(java.lang.String)

append

public StringBuffer append(double d)

Appends the string representation of the double argument to this sequence.

The argument is converted to a string as if by the method String.valueOf, and the characters of that string are then appended to this sequence.

参数：

d - a double.

返回：

a reference to this object.

另请参见：

String.valueOf(double), append(java.lang.String)

delete

public StringBuffer delete(int start,
                           int end)

Removes the characters in a substring of this sequence. The substring begins at the specified start and extends to the character at index end - 1 or to the end of the sequence if no such character exists. If start is equal to end, no changes are made.

参数：

start - The beginning index, inclusive.

end - The ending index, exclusive.

返回：

This object.

抛出：

StringIndexOutOfBoundsException - if start is negative, greater than length(), or greater than end.

从以下版本开始：

1.2

deleteCharAt

public StringBuffer deleteCharAt(int index)

Removes the char at the specified position in this sequence. This sequence is shortened by one char.

Note: If the character at the given index is a supplementary character, this method does not remove the entire character. If correct handling of supplementary characters is required, determine the number of chars to remove by calling Character.charCount(thisSequence.codePointAt(index)), where thisSequence is this sequence.

参数：

index - Index of char to remove

返回：

This object.

抛出：

StringIndexOutOfBoundsException - if the index is negative or greater than or equal to length().

从以下版本开始：

1.2

replace

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

Replaces the characters in a substring of this sequence with characters in the specified String. The substring begins at the specified start and extends to the character at index end - 1 or to the end of the sequence if no such character exists. First the characters in the substring are removed and then the specified String is inserted at start. (This sequence will be lengthened to accommodate the specified String if necessary.)

参数：

start - The beginning index, inclusive.

end - The ending index, exclusive.

str - String that will replace previous contents.

返回：

This object.

抛出：

StringIndexOutOfBoundsException - if start is negative, greater than length(), or greater than end.

从以下版本开始：

1.2

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.

从以下版本开始：

1.2

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, end)

behaves in exactly the same way as the invocation

 sb.substring(begin, end)

This method is provided so that this class can implement the CharSequence interface.

指定者：

接口 CharSequence 中的 subSequence

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)

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.

从以下版本开始：

1.2

insert

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

Inserts the string representation of a subarray of the str array argument into this sequence. The subarray begins at the specified offset and extends len chars. The characters of the subarray are inserted into this sequence at the position indicated by index. The length of this sequence increases by len chars.

参数：

index - position at which to insert subarray.

str - A char array.

offset - the index of the first char in subarray to be inserted.

len - the number of chars in the subarray to be inserted.

返回：

This object

抛出：

StringIndexOutOfBoundsException - if index is negative or greater than length(), or offset or len are negative, or (offset+len) is greater than str.length.

从以下版本开始：

1.2

insert

public StringBuffer insert(int offset,
                           Object obj)

Inserts the string representation of the Object argument into this character sequence.

The second argument is converted to a string as if by the method String.valueOf, and the characters of that string are then inserted into this sequence at the indicated offset.

The offset argument must be greater than or equal to 0, and less than or equal to the length of this sequence.

参数：

offset - the offset.

obj - an Object.

返回：

a reference to this object.

抛出：

StringIndexOutOfBoundsException - if the offset is invalid.

另请参见：

String.valueOf(java.lang.Object), insert(int, java.lang.String), length()

insert

public StringBuffer insert(int offset,
                           String str)

Inserts the string into this character sequence.

The characters of the String argument are inserted, in order, into this sequence at the indicated offset, moving up any characters originally above that position and increasing the length of this sequence by the length of the argument. If str is null, then the four characters "null" are inserted into this sequence.

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 offset
• the character at index k-offset in the argument str, if k is not less than offset but is less than offset+str.length()
• the character at index k-str.length() in the old character sequence, if k is not less than offset+str.length()

The offset argument must be greater than or equal to 0, and less than or equal to the length of this sequence.

参数：

offset - the offset.

str - a string.

返回：

a reference to this object.

抛出：

StringIndexOutOfBoundsException - if the offset is invalid.

另请参见：

length()

insert

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

Inserts the string representation of the char array argument into this sequence.

The characters of the array argument are inserted into the contents of this sequence at the position indicated by offset. The length of this sequence increases by the length of the argument.

The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(char[]) and the characters of that string were then inserted into this character sequence at the position indicated by offset.

参数：

offset - the offset.

str - a character array.

返回：

a reference to this object.

抛出：

StringIndexOutOfBoundsException - if the offset is invalid.

insert

public StringBuffer insert(int dstOffset,
                           CharSequence s)

Inserts the specified CharSequence into this sequence.

The characters of the CharSequence argument are inserted, in order, into this sequence at the indicated offset, moving up any characters originally above that position and increasing the length of this sequence by the length of the argument s.

The result of this method is exactly the same as if it were an invocation of this object's insert(dstOffset, s, 0, s.length()) method.

If s is null, then the four characters "null" are inserted into this sequence.

参数：

dstOffset - the offset.

s - the sequence to be inserted

返回：

a reference to this object.

抛出：

IndexOutOfBoundsException - if the offset is invalid.

从以下版本开始：

1.5

insert

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

Inserts a subsequence of the specified CharSequence into this sequence.

The subsequence of the argument s specified by start and end are inserted, in order, into this sequence at the specified destination offset, moving up any characters originally above that position. The length of this sequence is increased by end - start.

The character at index k in this sequence becomes equal to:

• the character at index k in this sequence, if k is less than dstOffset
• the character at index k+start-dstOffset in the argument s, if k is greater than or equal to dstOffset but is less than dstOffset+end-start
• the character at index k-(end-start) in this sequence, if k is greater than or equal to dstOffset+end-start

The dstOffset argument must be greater than or equal to 0, and less than or equal to the length of this sequence.

The start argument must be nonnegative, and not greater than end.

The end argument must be greater than or equal to start, and less than or equal to the length of s.

If s is null, then this method inserts characters as if the s parameter was a sequence containing the four characters "null".

参数：

dstOffset - the offset in this sequence.

s - the sequence to be inserted.

start - the starting index of the subsequence to be inserted.

end - the end index of the subsequence to be inserted.

返回：

a reference to this object.

抛出：

IndexOutOfBoundsException - if dstOffset is negative or greater than this.length(), or start or end are negative, or start is greater than end or end is greater than s.length()

从以下版本开始：

1.5

insert

public StringBuffer insert(int offset,
                           boolean b)

Inserts the string representation of the boolean argument into this sequence.

The second argument is converted to a string as if by the method String.valueOf, and the characters of that string are then inserted into this sequence at the indicated offset.

The offset argument must be greater than or equal to 0, and less than or equal to the length of this sequence.

参数：

offset - the offset.

b - a boolean.

返回：

a reference to this object.

抛出：

StringIndexOutOfBoundsException - if the offset is invalid.

另请参见：

String.valueOf(boolean), insert(int, java.lang.String), length()

insert

public StringBuffer insert(int offset,
                           char c)

Inserts the string representation of the char argument into this sequence.

The second argument is inserted into the contents of this sequence at the position indicated by offset. The length of this sequence increases by one.

The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(char) and the character in that string were then inserted into this character sequence at the position indicated by offset.

The offset argument must be greater than or equal to 0, and less than or equal to the length of this sequence.

参数：

offset - the offset.

c - a char.

返回：

a reference to this object.

抛出：

IndexOutOfBoundsException - if the offset is invalid.

另请参见：

length()

insert

public StringBuffer insert(int offset,
                           int i)

Inserts the string representation of the second int argument into this sequence.

The second argument is converted to a string as if by the method String.valueOf, and the characters of that string are then inserted into this sequence at the indicated offset.

The offset argument must be greater than or equal to 0, and less than or equal to the length of this sequence.

参数：

offset - the offset.

i - an int.

返回：

a reference to this object.

抛出：

StringIndexOutOfBoundsException - if the offset is invalid.

另请参见：

String.valueOf(int), insert(int, java.lang.String), length()

insert

public StringBuffer insert(int offset,
                           long l)

Inserts the string representation of the long argument into this sequence.

The second argument is converted to a string as if by the method String.valueOf, and the characters of that string are then inserted into this sequence at the position indicated by offset.

The offset argument must be greater than or equal to 0, and less than or equal to the length of this sequence.

参数：

offset - the offset.

l - a long.

返回：

a reference to this object.

抛出：

StringIndexOutOfBoundsException - if the offset is invalid.

另请参见：

String.valueOf(long), insert(int, java.lang.String), length()

insert

public StringBuffer insert(int offset,
                           float f)

Inserts the string representation of the float argument into this sequence.

The second argument is converted to a string as if by the method String.valueOf, and the characters of that string are then inserted into this sequence at the indicated offset.

The offset argument must be greater than or equal to 0, and less than or equal to the length of this sequence.

参数：

offset - the offset.

f - a float.

返回：

a reference to this object.

抛出：

StringIndexOutOfBoundsException - if the offset is invalid.

另请参见：

String.valueOf(float), insert(int, java.lang.String), length()

insert

public StringBuffer insert(int offset,
                           double d)

Inserts the string representation of the double argument into this sequence.

The second argument is converted to a string as if by the method String.valueOf, and the characters of that string are then inserted into this sequence at the indicated offset.

The offset argument must be greater than or equal to 0, and less than or equal to the length of this sequence.

参数：

offset - the offset.

d - a double.

返回：

a reference to this object.

抛出：

StringIndexOutOfBoundsException - if the offset is invalid.

另请参见：

String.valueOf(double), insert(int, java.lang.String), length()

indexOf

public int indexOf(String str)

Returns the index within this string of the first occurrence of the specified substring. The integer returned is the smallest value k such that:

 this.toString().startsWith(str, k)
 

is true.

参数：

str - any string.

返回：

if the string argument occurs as a substring within this object, then the index of the first character of the first such substring is returned; if it does not occur as a substring, -1 is returned.

抛出：

NullPointerException - if str is null.

从以下版本开始：

1.4

indexOf

public int indexOf(String str,
                   int fromIndex)

Returns the index within this string of the first occurrence of the specified substring, starting at the specified index. The integer returned is the smallest value k for which:

     k >= Math.min(fromIndex, str.length()) &&
                   this.toString().startsWith(str, k)
 

If no such value of k exists, then -1 is returned.

参数：

str - the substring for which to search.

fromIndex - the index from which to start the search.

返回：

the index within this string of the first occurrence of the specified substring, starting at the specified index.

抛出：

NullPointerException - if str is null.

从以下版本开始：

1.4

lastIndexOf

public int lastIndexOf(String str)

Returns the index within this string of the rightmost occurrence of the specified substring. The rightmost empty string "" is considered to occur at the index value this.length(). The returned index is the largest value k such that

 this.toString().startsWith(str, k)
 

is true.

参数：

str - the substring to search for.

返回：

if the string argument occurs one or more times as a substring within this object, then the index of the first character of the last such substring is returned. If it does not occur as a substring, -1 is returned.

抛出：

NullPointerException - if str is null.

从以下版本开始：

1.4

lastIndexOf

public int lastIndexOf(String str,
                       int fromIndex)

Returns the index within this string of the last occurrence of the specified substring. The integer returned is the largest value k such that:

     k <= Math.min(fromIndex, str.length()) &&
                   this.toString().startsWith(str, k)
 

If no such value of k exists, then -1 is returned.

参数：

str - the substring to search for.

fromIndex - the index to start the search from.

返回：

the index within this sequence of the last occurrence of the specified substring.

抛出：

NullPointerException - if str is null.

从以下版本开始：

1.4

reverse

public StringBuffer reverse()

Causes this character sequence to be replaced by the reverse of the sequence. If there are any surrogate pairs included in the sequence, these are treated as single characters for the reverse operation. Thus, the order of the high-low surrogates is never reversed. Let n be the character length of this character sequence (not the length in char values) just prior to execution of the reverse method. Then the character at index k in the new character sequence is equal to the character at index n-k-1 in the old character sequence.

Note that the reverse operation may result in producing surrogate pairs that were unpaired low-surrogates and high-surrogates before the operation. For example, reversing "\uDC00\uD800" produces "\uD800\uDC00" which is a valid surrogate pair.

返回：

a reference to this object.

从以下版本开始：

JDK1.0.2

toString

public String toString()

Returns a string representing the data in this sequence. A new String object is allocated and initialized to contain the character sequence currently represented by this object. This String is then returned. Subsequent changes to this sequence do not affect the contents of the String.

指定者：

接口 CharSequence 中的 toString

返回：

a string representation of this sequence of characters.

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