public final class

StringBuffer

extends Object
implements Appendable CharSequence
java.lang.Object
   ↳ java.lang.StringBuffer

Class Overview

A string buffer implements a 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.

String buffers are used by the compiler to implement the binary string concatenation operator +. For example, the code: 

 x = "a" + 4 + "c"

is compiled to the equivalent of: 

 x = new StringBuffer().append("a").append(4).append("c").toString()
which creates a new string buffer (initially empty), appends the string representation of each operand to the string buffer in turn, and then converts the contents of the string buffer to a string. Overall, this avoids creating many temporary strings.

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).

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.

See Also

Summary

Public Constructors
StringBuffer()
Constructs a string buffer with no characters in it and an initial capacity of 16 characters.
StringBuffer(int length)
Constructs a string buffer with no characters in it and an initial capacity specified by the length argument.
StringBuffer(String str)
Constructs a string buffer so that it represents the same sequence of characters as the string argument; in other words, the initial contents of the string buffer is a copy of the argument string.
Public Methods
StringBuffer append(boolean b)
Appends the string representation of the boolean argument to the string buffer.
StringBuffer append(long l)
Appends the string representation of the long argument to this string buffer.
synchronized StringBuffer append(char c)
Appends the string representation of the char argument to this string buffer.
synchronized StringBuffer append(Object obj)
Appends the string representation of the Object argument to this string buffer.
synchronized StringBuffer append(char[] str, int offset, int len)
Appends the string representation of a subarray of the char array argument to this string buffer.
AbstractStringBuilder append(double d)
Appends the string representation of the double argument to this sequence.
synchronized StringBuffer append(char[] str)
Appends the string representation of the char array argument to this string buffer.
synchronized StringBuffer append(String str)
Appends the string to this string buffer.
AbstractStringBuilder append(StringBuffer sb)
AbstractStringBuilder append(float f)
Appends the string representation of the float argument to this sequence.
StringBuffer append(int i)
Appends the string representation of the int argument to this string buffer.
AbstractStringBuilder append(CharSequence s, int start, int end)
Appends a subsequence of the specified CharSequence to this sequence.
AbstractStringBuilder append(CharSequence s)
Appends the character sequence csq.
AbstractStringBuilder appendCodePoint(int codePoint)
Appends the string representation of the codePoint argument to this sequence.
int capacity()
Returns the current capacity of the String buffer.
synchronized char charAt(int index)
The specified character of the sequence currently represented by the string buffer, as indicated by the index argument, is returned.
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.
synchronized StringBuffer delete(int start, int end)
Removes the characters in a substring of this StringBuffer.
synchronized StringBuffer deleteCharAt(int index)
Removes the character at the specified position in this StringBuffer (shortening the StringBuffer by one character).
synchronized void ensureCapacity(int minimumCapacity)
Ensures that the capacity of the buffer is at least equal to the specified minimum.
synchronized void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
Characters are copied from this string buffer into the destination character array dst.
int indexOf(String str)
Returns the index within this string of the first occurrence of the specified substring.
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.
synchronized StringBuffer insert(int offset, char[] str)
Inserts the string representation of the char array argument into this string buffer.
AbstractStringBuilder insert(int offset, float f)
Inserts the string representation of the float argument into this sequence.
AbstractStringBuilder insert(int dstOffset, CharSequence s)
Inserts the specified CharSequence into this sequence.
synchronized StringBuffer insert(int offset, char c)
Inserts the string representation of the char argument into this string buffer.
StringBuffer insert(int offset, long l)
Inserts the string representation of the long argument into this string buffer.
AbstractStringBuilder insert(int index, char[] str, int offset, int len)
Inserts the string representation of a subarray of the str array argument into this sequence.
StringBuffer insert(int offset, int i)
Inserts the string representation of the second int argument into this string buffer.
synchronized StringBuffer insert(int offset, String str)
Inserts the string into this string buffer.
AbstractStringBuilder insert(int offset, double d)
Inserts the string representation of the double argument into this sequence.
AbstractStringBuilder insert(int dstOffset, CharSequence s, int start, int end)
Inserts a subsequence of the specified CharSequence into this sequence.
synchronized StringBuffer insert(int offset, Object obj)
Inserts the string representation of the Object argument into this string buffer.
StringBuffer insert(int offset, boolean b)
Inserts the string representation of the boolean argument into this string buffer.
int lastIndexOf(String str, int fromIndex)
Returns the index within this string of the last occurrence of the specified substring.
int lastIndexOf(String str)
Returns the index within this string of the rightmost occurrence of the specified substring.
int length()
Returns the length (character count) of this string buffer.
int offsetByCodePoints(int index, int codePointOffset)
Returns the index within this sequence that is offset from the given index by codePointOffset code points.
AbstractStringBuilder replace(int start, int end, String str)
Replaces the characters in a substring of this sequence with characters in the specified String.
synchronized StringBuffer reverse()
The character sequence contained in this string buffer is replaced by the reverse of the sequence.
synchronized void setCharAt(int index, char ch)
The character at the specified index of this string buffer is set to ch.
synchronized void setLength(int newLength)
Sets the length of this String buffer.
CharSequence subSequence(int start, int end)
Returns a new character sequence that is a subsequence of this sequence.
String substring(int start, int end)
Returns a new String that contains a subsequence of characters currently contained in this sequence.
String substring(int start)
Returns a new String that contains a subsequence of characters currently contained in this character sequence.
String toString()
Converts to a string representing the data in this string buffer.
void trimToSize()
Attempts to reduce storage used for the character sequence.
[Expand]
Inherited Methods
From class java.lang.Object
From interface java.lang.Appendable
From interface java.lang.CharSequence

Public Constructors

public StringBuffer ()

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

public StringBuffer (int length)

Constructs a string buffer with no characters in it and an initial capacity specified by the length argument.

Parameters
length the initial capacity.
Throws
NegativeArraySizeException if the length argument is less than 0.

public StringBuffer (String str)

Constructs a string buffer so that it represents the same sequence of characters as the string argument; in other words, the initial contents of the string buffer is a copy of the argument string. The initial capacity of the string buffer is 16 plus the length of the string argument.

Parameters
str the initial contents of the buffer.

Public Methods

public StringBuffer append (boolean b)

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

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 buffer.

Parameters
b a boolean.
Returns
  • a reference to this StringBuffer.
See Also

public StringBuffer append (long l)

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

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 buffer.

Parameters
l a long.
Returns
  • a reference to this StringBuffer object.
See Also

public synchronized StringBuffer append (char c)

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

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

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

Parameters
c a char.
Returns
  • a reference to this StringBuffer object.

public synchronized StringBuffer append (Object obj)

Appends the string representation of the Object argument to this string buffer.

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 buffer.

Parameters
obj an Object.
Returns
  • a reference to this StringBuffer object.
See Also

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

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

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

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

Parameters
str the characters to be appended.
offset the index of the first character to append.
len the number of characters to append.
Returns
  • a reference to this StringBuffer object.

public AbstractStringBuilder 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.

Parameters
d a double.
Returns
  • a reference to this object.

public synchronized StringBuffer append (char[] str)

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

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

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

Parameters
str the characters to be appended.
Returns
  • a reference to this StringBuffer object.

public synchronized StringBuffer append (String str)

Appends the string to this string buffer.

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

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

Parameters
str a string.
Returns
  • a reference to this StringBuffer.

public AbstractStringBuilder append (StringBuffer sb)

public AbstractStringBuilder 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.

Parameters
f a float.
Returns
  • a reference to this object.

public StringBuffer append (int i)

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

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 buffer.

Parameters
i an int.
Returns
  • a reference to this StringBuffer object.
See Also

public AbstractStringBuilder 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".

Parameters
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.
Returns
  • a reference to this object.
Throws
IndexOutOfBoundsException if start or end are negative, or start is greater than end or end is greater than s.length()

public AbstractStringBuilder append (CharSequence s)

Appends the character sequence csq. Implementation classes may not append the whole sequence, for example if the target is a buffer with limited size.

If csq is null, the characters "null" are appended.

Parameters
s the character sequence to append.
Returns
  • this Appendable.

public AbstractStringBuilder appendCodePoint (int codePoint)

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

The argument is appended to the contents of this sequence.

Parameters
codePoint a Unicode code point
Returns
  • a reference to this object.
Throws
IllegalArgumentException if the specified codePoint isn't a valid Unicode code point

public int capacity ()

Returns the current capacity of the String buffer. The capacity is the amount of storage available for newly inserted characters; beyond which an allocation will occur.

Returns
  • the current capacity of this string buffer.

public synchronized char charAt (int index)

The specified character of the sequence currently represented by the string buffer, as indicated by the index argument, is returned. The first character of a string buffer is at index 0, the next at index 1, and so on, for array indexing.

The index argument must be greater than or equal to 0, and less than the length of this string buffer.

Parameters
index the index of the desired character.
Returns
  • the character at the specified index of this string buffer.
Throws
IndexOutOfBoundsException if index is negative or greater than or equal to length() .
See Also

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.

Parameters
index the index to the char values
Returns
  • the code point value of the character at the index
Throws
IndexOutOfBoundsException if the index argument is negative or not less than the length of this sequence.

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.

Parameters
index the index following the code point that should be returned
Returns
  • the Unicode code point value before the given index.
Throws
IndexOutOfBoundsException if the index argument is less than 1 or greater than the length of this sequence.

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.

Parameters
beginIndex the index to the first char of the text range.
endIndex the index after the last char of the text range.
Returns
  • the number of Unicode code points in the specified text range
Throws
IndexOutOfBoundsException if the beginIndex is negative, or endIndex is larger than the length of this sequence, or beginIndex is larger than endIndex.

public synchronized StringBuffer delete (int start, int end)

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

Parameters
start The beginning index, inclusive.
end The ending index, exclusive.
Returns
  • This string buffer.
Throws
StringIndexOutOfBoundsException if start is negative, greater than length(), or greater than end.

public synchronized StringBuffer deleteCharAt (int index)

Removes the character at the specified position in this StringBuffer (shortening the StringBuffer by one character).

Parameters
index Index of character to remove
Returns
  • This string buffer.
Throws
StringIndexOutOfBoundsException if the index is negative or greater than or equal to length().

public synchronized void ensureCapacity (int minimumCapacity)

Ensures that the capacity of the buffer is at least equal to the specified minimum. If the current capacity of this string buffer is less than the argument, then a new internal buffer 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.

Parameters
minimumCapacity the minimum desired capacity.

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

Characters are copied from this string buffer 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

Parameters
srcBegin start copying at this offset in the string buffer.
srcEnd stop copying at this offset in the string buffer.
dst the array to copy the data into.
dstBegin offset into dst.
Throws
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() , the current length of this string buffer.
  • dstBegin+srcEnd-srcBegin is greater than dst.length

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.

Parameters
str any string.
Returns
  • 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.
Throws
NullPointerException if str is null.

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.

Parameters
str the substring for which to search.
fromIndex the index from which to start the search.
Returns
  • the index within this string of the first occurrence of the specified substring, starting at the specified index.
Throws
NullPointerException if str is null.

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

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

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

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

Parameters
offset the offset.
str a character array.
Returns
  • a reference to this StringBuffer object.
Throws
StringIndexOutOfBoundsException if the offset is invalid.

public AbstractStringBuilder 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.

Parameters
offset the offset.
f a float.
Returns
  • a reference to this object.
Throws
StringIndexOutOfBoundsException if the offset is invalid.

public AbstractStringBuilder 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.

Parameters
dstOffset the offset.
s the sequence to be inserted
Returns
  • a reference to this object.
Throws
IndexOutOfBoundsException if the offset is invalid.

public synchronized StringBuffer insert (int offset, char c)

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

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

The overall effect is exactly as if the argument were converted to a string by the method valueOf(char) and the character in that string were then inserted into this StringBuffer object 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 string buffer.

Parameters
offset the offset.
c a char.
Returns
  • a reference to this StringBuffer object.
Throws
IndexOutOfBoundsException if the offset is invalid.
See Also

public StringBuffer insert (int offset, long l)

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

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 string buffer 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 string buffer.

Parameters
offset the offset.
l a long.
Returns
  • a reference to this StringBuffer object.
Throws
StringIndexOutOfBoundsException if the offset is invalid.
See Also

public AbstractStringBuilder 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.

Parameters
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.
Returns
  • This object
Throws
StringIndexOutOfBoundsException if index is negative or greater than length(), or offset or len are negative, or (offset+len) is greater than str.length.

public StringBuffer insert (int offset, int i)

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

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 string buffer 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 string buffer.

Parameters
offset the offset.
i an int.
Returns
  • a reference to this StringBuffer object.
Throws
StringIndexOutOfBoundsException if the offset is invalid.
See Also

public synchronized StringBuffer insert (int offset, String str)

Inserts the string into this string buffer.

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

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 string buffer.

Parameters
offset the offset.
str a string.
Returns
  • a reference to this StringBuffer object.
Throws
StringIndexOutOfBoundsException if the offset is invalid.
See Also

public AbstractStringBuilder 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.

Parameters
offset the offset.
d a double.
Returns
  • a reference to this object.
Throws
StringIndexOutOfBoundsException if the offset is invalid.

public AbstractStringBuilder 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".

Parameters
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.
Returns
  • a reference to this object.
Throws
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()

public synchronized StringBuffer insert (int offset, Object obj)

Inserts the string representation of the Object argument into this string buffer.

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 string buffer 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 string buffer.

Parameters
offset the offset.
obj an Object.
Returns
  • a reference to this StringBuffer object.
Throws
StringIndexOutOfBoundsException if the offset is invalid.
See Also

public StringBuffer insert (int offset, boolean b)

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

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 string buffer 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 string buffer.

Parameters
offset the offset.
b a boolean.
Returns
  • a reference to this StringBuffer object.
Throws
StringIndexOutOfBoundsException if the offset is invalid.
See Also

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.

Parameters
str the substring to search for.
fromIndex the index to start the search from.
Returns
  • the index within this sequence of the last occurrence of the specified substring.
Throws
NullPointerException if str is null.

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.

Parameters
str the substring to search for.
Returns
  • 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.
Throws
NullPointerException if str is null.

public int length ()

Returns the length (character count) of this string buffer.

Returns
  • the length of the sequence of characters currently represented by this string buffer.

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.

Parameters
index the index to be offset
codePointOffset the offset in code points
Returns
  • the index within this sequence
Throws
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.

public AbstractStringBuilder 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.)

Parameters
start The beginning index, inclusive.
end The ending index, exclusive.
str String that will replace previous contents.
Returns
  • This object.
Throws
StringIndexOutOfBoundsException if start is negative, greater than length(), or greater than end.

public synchronized StringBuffer reverse ()

The character sequence contained in this string buffer is replaced by the reverse of the sequence.

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

Returns
  • a reference to this StringBuffer object..

public synchronized void setCharAt (int index, char ch)

The character at the specified index of this string buffer is set to ch. The string buffer 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 offset argument must be greater than or equal to 0, and less than the length of this string buffer.

Parameters
index the index of the character to modify.
ch the new character.
Throws
IndexOutOfBoundsException if index is negative or greater than or equal to length() .
See Also

public synchronized void setLength (int newLength)

Sets the length of this String buffer. This string buffer is altered to represent 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 ''. In other words, if the newLength argument is less than the current length of the string buffer, the string buffer is truncated to contain exactly the number of characters given by the newLength argument.

If the newLength argument is greater than or equal to the current length, sufficient null characters ('\u0000') are appended to the string buffer so that length becomes the newLength argument.

The newLength argument must be greater than or equal to 0.

Parameters
newLength the new length of the buffer.
Throws
IndexOutOfBoundsException if the newLength argument is negative.
See Also

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.

Parameters
start the start index, inclusive.
end the end index, exclusive.
Returns
  • the specified subsequence.

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.

Parameters
start The beginning index, inclusive.
end The ending index, exclusive.
Returns
  • The new string.
Throws
StringIndexOutOfBoundsException if start or end are negative or greater than length(), or start is greater than end.

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.

Parameters
start The beginning index, inclusive.
Returns
  • The new string.
Throws
StringIndexOutOfBoundsException if start is less than zero, or greater than the length of this object.

public String toString ()

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

Implementation advice: This method can be coded so as to create a new String object without allocating new memory to hold a copy of the character sequence. Instead, the string can share the memory used by the string buffer. Any subsequent operation that alters the content or capacity of the string buffer must then make a copy of the internal buffer at that time. This strategy is effective for reducing the amount of memory allocated by a string concatenation operation when it is implemented using a string buffer.

Returns
  • a string representation of the string buffer.

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.