public final class StringBuffer extends Object implements Serializable, CharSequence
A thread-safe, mutable sequence of characters. A string buffer is like a String, but can be modified. At any point in time it contains some particular sequence of characters, but the length and content of the sequence can be changed through certain method calls.
String buffers are safe for use by multiple threads. The methods are synchronized where necessary so that all the operations on any particular instance behave as if they occur in some serial order that is consistent with the order of the method calls made by each of the individual threads involved.
The principal operations on a StringBuffer are the append and insert methods, which are overloaded so as to accept data of any type. Each effectively converts a given datum to a string and then appends or inserts the characters of that string to the string buffer. The append method always adds these characters at the end of the buffer; the insert method adds the characters at a specified point.
For example, if z refers to a string buffer object whose current contents are "start", then the method call z.append("le") would cause the string buffer to contain "startle", whereas z.insert(4, "le") would alter the string buffer to contain "starlet".
In general, if sb refers to an instance of a StringBuffer, then sb.append(x) has the same effect as sb.insert(sb.length(), x).
Whenever an operation occurs involving a source sequence (such as appending or inserting from a source sequence), this class synchronizes only on the string buffer performing the operation, not on the source. Note that while StringBuffer is designed to be safe to use concurrently from multiple threads, if the constructor or the append or insert operation is passed a source sequence that is shared across threads, the calling code must ensure that the operation has a consistent and unchanging view of the source sequence for the duration of the operation. This could be satisfied by the caller holding a lock during the operation's call, by using an immutable source sequence, or by not sharing the source sequence across threads.
Every string buffer has a capacity. As long as the length of the character sequence contained in the string buffer does not exceed the capacity, it is not necessary to allocate a new internal buffer array. If the internal buffer overflows, it is automatically made larger.
Unless otherwise noted, passing a null argument to a constructor or method in this class will cause a NullPointerException to be thrown.
As of release JDK 5, this class has been supplemented with an equivalent class designed for use by a single thread, StringBuilder. The StringBuilder class should generally be used in preference to this one, as it supports all of the same operations but it is faster, as it performs no synchronization.
StringBuilder, String, Serialized Formpublic StringBuffer()
Constructs a string buffer with no characters in it and an initial capacity of 16 characters.
public StringBuffer(int capacity)
Constructs a string buffer with no characters in it and the specified initial capacity.
capacity - the initial capacity.NegativeArraySizeException - if the capacity argument is less than 0.public StringBuffer(String str)
Constructs a string buffer initialized to the contents of the specified string. The initial capacity of the string buffer is 16 plus the length of the string argument.
str - the initial contents of the buffer.public StringBuffer(CharSequence seq)
Constructs a string buffer that contains the same characters as the specified CharSequence. The initial capacity of the string buffer is 16 plus the length of the CharSequence argument.
If the length of the specified CharSequence is less than or equal to zero, then an empty buffer of capacity 16 is returned.
seq - the sequence to copy.public int length()
Returns the length (character count).
length in interface CharSequence
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.
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:
minimumCapacity argument. 2. 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. minimumCapacity - the minimum desired capacity.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.
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.
newLength - the new lengthIndexOutOfBoundsException - if the newLength argument is negative.length()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.
charAt in interface CharSequence
index - the index of the desired char value.char value at the specified index.IndexOutOfBoundsException - if index is negative or greater than or equal to length().length()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.
index - the index to the char valuesindex
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.
index - the index following the code point that should be returnedpublic 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.
beginIndex - the index to the first char of the text range.endIndex - the index after the last char of the text range.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.
index - the index to be offsetcodePointOffset - the offset in code pointspublic 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
srcBegin - start copying at this offset.srcEnd - stop copying at this offset.dst - the array to copy the data into.dstBegin - offset into dst.IndexOutOfBoundsException - if any of the following is true: srcBegin is negative dstBegin is negative srcBegin argument is greater than the srcEnd argument. srcEnd is greater than this.length(). dstBegin+srcEnd-srcBegin is greater than dst.length 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.
index - the index of the character to modify.ch - the new character.IndexOutOfBoundsException - if index is negative or greater than or equal to length().length()public StringBuffer append(Object obj)
Appends the string representation of the Object argument.
The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(Object), and the characters of that string were then appended to this character sequence.
obj - an Object.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.
str - a string.public StringBuffer append(StringBuffer sb)
Appends the specified StringBuffer to this sequence.
The characters of the StringBuffer argument are appended, in order, to the contents of this StringBuffer, increasing the length of this StringBuffer by the length of the argument. If sb is null, then the four characters "null" are appended to this StringBuffer.
Let n be the length of the old character sequence, the one contained in the StringBuffer just prior to execution of the append method. Then the character at index k in the new character sequence is equal to the character at index k in the old character sequence, if k is less than n; otherwise, it is equal to the character at index k-n in the argument sb.
This method synchronizes on this, the destination object, but does not synchronize on the source (sb).
sb - the StringBuffer to append.public StringBuffer append(CharSequence s)
Appends the specified CharSequence to this sequence.
The characters of the CharSequence argument are appended, in order, increasing the length of this sequence by the length of the argument.
The result of this method is exactly the same as if it were an invocation of this.append(s, 0, s.length());
This method synchronizes on this, the destination object, but does not synchronize on the source (s).
If s is null, then the four characters "null" are appended.
append in interface Appendable
s - the CharSequence to 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".
append in interface Appendable
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.IndexOutOfBoundsException - if start is negative, or start is greater than end or end is greater than s.length()
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.
str - the characters to be appended.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.
str - the characters to be appended.offset - the index of the first char to append.len - the number of chars to append.IndexOutOfBoundsException - if offset < 0 or len < 0 or offset+len > str.length
public StringBuffer append(boolean b)
Appends the string representation of the boolean argument to the sequence.
The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(boolean), and the characters of that string were then appended to this character sequence.
b - a boolean.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.
append in interface Appendable
c - a char.public StringBuffer append(int i)
Appends the string representation of the int argument to this sequence.
The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(int), and the characters of that string were then appended to this character sequence.
i - an int.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.
codePoint - a Unicode code pointpublic StringBuffer append(long lng)
Appends the string representation of the long argument to this sequence.
The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(long), and the characters of that string were then appended to this character sequence.
lng - a long.public StringBuffer append(float f)
Appends the string representation of the float argument to this sequence.
The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(float), and the characters of that string were then appended to this character sequence.
f - a float.public StringBuffer append(double d)
Appends the string representation of the double argument to this sequence.
The overall effect is exactly as if the argument were converted to a string by the method String.valueOf(double), and the characters of that string were then appended to this character sequence.
d - a double.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.
start - The beginning index, inclusive.end - The ending index, exclusive.StringIndexOutOfBoundsException - if start is negative, greater than length(), or greater than end.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.
index - Index of char to removeStringIndexOutOfBoundsException - if the index is negative or greater than or equal to length().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.)
start - The beginning index, inclusive.end - The ending index, exclusive.str - String that will replace previous contents.StringIndexOutOfBoundsException - if start is negative, greater than length(), or 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.
start - The beginning index, inclusive.StringIndexOutOfBoundsException - if start is less than zero, or greater than the length of this object.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.subSequence in interface CharSequence
start - the start index, inclusive.end - the end index, exclusive.IndexOutOfBoundsException - if start or end are negative, if end is greater than length(), or if start is greater than end
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.
start - The beginning index, inclusive.end - The ending index, exclusive.StringIndexOutOfBoundsException - if start or end are negative or greater than length(), or start is greater than end.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.
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.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,
Object obj) Inserts the string representation of the Object argument into this character sequence.
The overall effect is exactly as if the second argument were converted to a string by the method String.valueOf(Object), and the characters of that string were then inserted into this character 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.
offset - the offset.obj - an Object.StringIndexOutOfBoundsException - if the offset is invalid.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:
offset -offset in the argument str, if k is not less than offset but is less than offset+str.length() -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.
offset - the offset.str - a string.StringIndexOutOfBoundsException - if the offset is invalid.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 second 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 indicated offset.
The offset argument must be greater than or equal to 0, and less than or equal to the length of this sequence.
offset - the offset.str - a character array.StringIndexOutOfBoundsException - if the offset is invalid.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.
dstOffset - the offset.s - the sequence to be insertedIndexOutOfBoundsException - if the offset is invalid.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:
dstOffset +start-dstOffset in the argument s, if k is greater than or equal to dstOffset but is less than dstOffset+end-start -(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".
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.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 StringBuffer insert(int offset,
boolean b) Inserts the string representation of the boolean argument into this sequence.
The overall effect is exactly as if the second argument were converted to a string by the method String.valueOf(boolean), and the characters of that string were then inserted into this character 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.
offset - the offset.b - a boolean.StringIndexOutOfBoundsException - if the offset is invalid.public StringBuffer insert(int offset,
char c) Inserts the string representation of the char argument into this sequence.
The overall effect is exactly as if the second 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 indicated offset.
The offset argument must be greater than or equal to 0, and less than or equal to the length of this sequence.
offset - the offset.c - a char.IndexOutOfBoundsException - if the offset is invalid.public StringBuffer insert(int offset,
int i) Inserts the string representation of the second int argument into this sequence.
The overall effect is exactly as if the second argument were converted to a string by the method String.valueOf(int), and the characters of that string were then inserted into this character 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.
offset - the offset.i - an int.StringIndexOutOfBoundsException - if the offset is invalid.public StringBuffer insert(int offset,
long l) Inserts the string representation of the long argument into this sequence.
The overall effect is exactly as if the second argument were converted to a string by the method String.valueOf(long), and the characters of that string were then inserted into this character 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.
offset - the offset.l - a long.StringIndexOutOfBoundsException - if the offset is invalid.public StringBuffer insert(int offset,
float f) Inserts the string representation of the float argument into this sequence.
The overall effect is exactly as if the second argument were converted to a string by the method String.valueOf(float), and the characters of that string were then inserted into this character 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.
offset - the offset.f - a float.StringIndexOutOfBoundsException - if the offset is invalid.public StringBuffer insert(int offset,
double d) Inserts the string representation of the double argument into this sequence.
The overall effect is exactly as if the second argument were converted to a string by the method String.valueOf(double), and the characters of that string were then inserted into this character 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.
offset - the offset.d - a double.StringIndexOutOfBoundsException - if the offset is invalid.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, <i>k</i>)is
true. str - any string.-1 is returned.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, this.length()) &&
this.toString().startsWith(str, k) If no such value of k exists, then -1 is returned. str - the substring for which to search.fromIndex - the index from which to start the search.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.
str - the substring to search for.-1 is returned.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, this.length()) &&
this.toString().startsWith(str, k) If no such value of k exists, then -1 is returned. str - the substring to search for.fromIndex - the index to start the search from.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.
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.
toString in interface CharSequence
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