StringBuilder
public final class StringBuilder
extends Object implements Appendable, CharSequence, Comparable<StringBuilder>, Serializable
A mutable sequence of characters. This class provides an API compatible with StringBuffer, but with no guarantee of synchronization. This class is designed for use as a drop-in replacement for StringBuffer in places where the string buffer was being used by a single thread (as is generally the case). Where possible, it is recommended that this class be used in preference to StringBuffer as it will be faster under most implementations.
The principal operations on a StringBuilder are the append and insert methods, which are overloaded so as to accept data of any type. Each effectively converts a given datum to a string and then appends or inserts the characters of that string to the string builder. The append method always adds these characters at the end of the builder; the insert method adds the characters at a specified point.
For example, if z refers to a string builder object whose current contents are "start", then the method call z.append("le") would cause the string builder to contain "startle", whereas z.insert(4, "le") would alter the string builder to contain "starlet".
In general, if sb refers to an instance of a StringBuilder, then sb.append(x) has the same effect as sb.insert(sb.length(), x).
Every string builder has a capacity. As long as the length of the character sequence contained in the string builder does not exceed the capacity, it is not necessary to allocate a new internal buffer. If the internal buffer overflows, it is automatically made larger.
Instances of StringBuilder are not safe for use by multiple threads. If such synchronization is required then it is recommended that StringBuffer be used.
Unless otherwise noted, passing a null argument to a constructor or method in this class will cause a NullPointerException to be thrown.
Summary
Public constructors |
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StringBuilder() Constructs a string builder with no characters in it and an initial capacity of 16 characters. |
StringBuilder(int capacity) Constructs a string builder with no characters in it and an initial capacity specified by the capacity argument. |
StringBuilder(CharSequence seq) Constructs a string builder that contains the same characters as the specified CharSequence. |
StringBuilder(String str) Constructs a string builder initialized to the contents of the specified string. |
Public methods |
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StringBuilder | append(boolean b) |
StringBuilder | append(long lng) |
StringBuilder | append(char c) Appends the specified character to this Appendable. |
StringBuilder | append(Object obj) |
StringBuilder | append(char[] str, int offset, int len) |
StringBuilder | append(double d) |
StringBuilder | append(char[] str) |
StringBuilder | append(String str) |
StringBuilder | append(StringBuffer sb) Appends the specified StringBuffer to this sequence. |
StringBuilder | append(float f) |
StringBuilder | append(int i) |
StringBuilder | append(CharSequence s, int start, int end) Appends a subsequence of the specified character sequence to this Appendable. |
StringBuilder | append(CharSequence s) Appends the specified character sequence to this Appendable. |
StringBuilder | appendCodePoint(int codePoint) |
int | capacity() Returns the current capacity. |
char | charAt(int index) Returns the char value in this sequence at the specified index. |
IntStream | chars() Returns a stream of int zero-extending the char values from this sequence. |
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. |
IntStream | codePoints() Returns a stream of code point values from this sequence. |
int | compareTo(StringBuilder another) Compares two StringBuilder instances lexicographically. |
StringBuilder | delete(int start, int end) |
StringBuilder | deleteCharAt(int index) |
void | ensureCapacity(int minimumCapacity) Ensures that the capacity is at least equal to the specified minimum. |
void | getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) Characters are copied from this sequence into the destination character array dst. |
int | indexOf(String str) |
int | indexOf(String str, int fromIndex) |
StringBuilder | insert(int offset, char[] str) |
StringBuilder | insert(int offset, float f) |
StringBuilder | insert(int dstOffset, CharSequence s) |
StringBuilder | insert(int offset, char c) |
StringBuilder | insert(int offset, long l) |
StringBuilder | insert(int index, char[] str, int offset, int len) |
StringBuilder | insert(int offset, int i) |
StringBuilder | insert(int offset, String str) |
StringBuilder | insert(int offset, double d) |
StringBuilder | insert(int dstOffset, CharSequence s, int start, int end) |
StringBuilder | insert(int offset, boolean b) |
StringBuilder | insert(int offset, Object obj) |
int | lastIndexOf(String str, int fromIndex) |
int | lastIndexOf(String str) |
int | length() Returns the length (character count). |
int | offsetByCodePoints(int index, int codePointOffset) Returns the index within this sequence that is offset from the given index by codePointOffset code points. |
StringBuilder | replace(int start, int end, String str) |
StringBuilder | reverse() |
void | setCharAt(int index, char ch) The character at the specified index is set to ch. |
void | setLength(int newLength) Sets the length of the character sequence. |
CharSequence | subSequence(int start, int end) Returns a new character sequence that is a subsequence of this sequence. |
String | substring(int start, 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() Returns a string representation of the object. |
void | trimToSize() Attempts to reduce storage used for the character sequence. |
Inherited methods |
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From class java.lang.Object Object | clone() Creates and returns a copy of this object. | boolean | equals(Object obj) Indicates whether some other object is "equal to" this one. | void | finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. | final Class<?> | getClass() Returns the runtime class of this Object. | int | hashCode() Returns a hash code value for the object. | final void | notify() Wakes up a single thread that is waiting on this object's monitor. | final void | notifyAll() Wakes up all threads that are waiting on this object's monitor. | String | toString() Returns a string representation of the object. | final void | wait(long timeoutMillis, int nanos) Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed. | final void | wait(long timeoutMillis) Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed. | final void | wait() Causes the current thread to wait until it is awakened, typically by being notified or interrupted. | |
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From interface java.lang.CharSequence abstract char | charAt(int index) Returns the char value at the specified index. | default IntStream | chars() Returns a stream of int zero-extending the char values from this sequence. | default IntStream | codePoints() Returns a stream of code point values from this sequence. | static int | compare(CharSequence cs1, CharSequence cs2) Compares two CharSequence instances lexicographically. | default boolean | isEmpty() Returns true if this character sequence is empty. | abstract int | length() Returns the length of this character sequence. | abstract CharSequence | subSequence(int start, int end) Returns a CharSequence that is a subsequence of this sequence. | abstract String | toString() Returns a string containing the characters in this sequence in the same order as this sequence. | |
| |
Public constructors
StringBuilder
public StringBuilder ()
Constructs a string builder with no characters in it and an initial capacity of 16 characters.
StringBuilder
public StringBuilder (int capacity)
Constructs a string builder with no characters in it and an initial capacity specified by the capacity argument.
| Parameters |
|---|
capacity | int: the initial capacity. |
StringBuilder
public StringBuilder (CharSequence seq)
Constructs a string builder that contains the same characters as the specified CharSequence. The initial capacity of the string builder is 16 plus the length of the CharSequence argument.
| Parameters |
|---|
seq | CharSequence: the sequence to copy. |
StringBuilder
public StringBuilder (String str)
Constructs a string builder initialized to the contents of the specified string. The initial capacity of the string builder is 16 plus the length of the string argument.
| Parameters |
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str | String: the initial contents of the buffer. |
Public methods
append
public StringBuilder append (char c)
Appends the specified character to this Appendable.
| Parameters |
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c | char: The character to append |
append
public StringBuilder append (char[] str, int offset, int len)
| Parameters |
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str | char |
offset | int |
len | int |
append
public StringBuilder append (StringBuffer sb)
Appends the specified StringBuffer to this sequence.
The characters of the StringBuffer argument are appended, in order, to this sequence, increasing the length of this sequence by the length of the argument. If sb is null, then the four characters "null" are appended to this sequence.
Let n be the length of this character sequence just prior to execution of the append method. Then the character at index k in the new character sequence is equal to the character at index k in the old character sequence, if k is less than n; otherwise, it is equal to the character at index k-n in the argument sb.
| Parameters |
|---|
sb | StringBuffer: the StringBuffer to append. |
append
public StringBuilder append (CharSequence s, int start, int end)
Appends a subsequence of the specified character sequence to this Appendable.
An invocation of this method of the form out.append(csq, start, end) when csq is not null, behaves in exactly the same way as the invocation
out.append(csq.subSequence(start, end))
| Parameters |
|---|
s | CharSequence: The character sequence from which a subsequence will be appended. If csq is null, then characters will be appended as if csq contained the four characters "null". |
start | int: The index of the first character in the subsequence |
end | int: The index of the character following the last character in the subsequence |
append
public StringBuilder append (CharSequence s)
Appends the specified character sequence to this Appendable.
Depending on which class implements the character sequence csq, the entire sequence may not be appended. For instance, if csq is a CharBuffer then the subsequence to append is defined by the buffer's position and limit.
| Parameters |
|---|
s | CharSequence: The character sequence to append. If csq is null, then the four characters "null" are appended to this Appendable. |
appendCodePoint
public StringBuilder appendCodePoint (int codePoint)
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.
| Returns |
|---|
int | the current capacity |
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.
| Parameters |
|---|
index | int: the index of the desired char value. |
| Returns |
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char | the char value at the specified index. |
chars
public IntStream chars ()
Returns a stream of int zero-extending the char values from this sequence. Any char which maps to a surrogate code point is passed through uninterpreted.
The stream binds to this sequence when the terminal stream operation commences (specifically, for mutable sequences the spliterator for the stream is late-binding). If the sequence is modified during that operation then the result is undefined.
| Returns |
|---|
IntStream | an IntStream of char values from this sequence |
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.
| Parameters |
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index | int: the index to the char values |
| Returns |
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int | the code point value of the character at the index |
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.
| Parameters |
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index | int: the index following the code point that should be returned |
| Returns |
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int | the Unicode code point value before the given index. |
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.
| Parameters |
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beginIndex | int: the index to the first char of the text range. |
endIndex | int: the index after the last char of the text range. |
| Returns |
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int | the number of Unicode code points in the specified text range |
| Throws |
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IndexOutOfBoundsException | if the beginIndex is negative, or endIndex is larger than the length of this sequence, or beginIndex is larger than endIndex. |
codePoints
public IntStream codePoints ()
Returns a stream of code point values from this sequence. Any surrogate pairs encountered in the sequence are combined as if by Character.toCodePoint and the result is passed to the stream. Any other code units, including ordinary BMP characters, unpaired surrogates, and undefined code units, are zero-extended to int values which are then passed to the stream.
The stream binds to this sequence when the terminal stream operation commences (specifically, for mutable sequences the spliterator for the stream is late-binding). If the sequence is modified during that operation then the result is undefined.
| Returns |
|---|
IntStream | an IntStream of Unicode code points from this sequence |
compareTo
public int compareTo (StringBuilder another)
Compares two StringBuilder instances lexicographically. This method follows the same rules for lexicographical comparison as defined in the CharSequence.compare(this, another) method.
For finer-grained, locale-sensitive String comparison, refer to Collator.
| Parameters |
|---|
another | StringBuilder: the StringBuilder to be compared with |
| Returns |
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int | the value 0 if this StringBuilder contains the same character sequence as that of the argument StringBuilder; a negative integer if this StringBuilder is lexicographically less than the StringBuilder argument; or a positive integer if this StringBuilder is lexicographically greater than the StringBuilder argument. |
delete
public StringBuilder delete (int start, int end)
| Parameters |
|---|
start | int |
end | int |
ensureCapacity
public void ensureCapacity (int minimumCapacity)
Ensures that the capacity is at least equal to the specified minimum. If the current capacity is less than the argument, then a new internal array is allocated with greater capacity. The new capacity is the larger of:
- The
minimumCapacity argument. - Twice the old capacity, plus
2.
If the
minimumCapacity argument is nonpositive, this method takes no action and simply returns. Note that subsequent operations on this object can reduce the actual capacity below that requested here.
| Parameters |
|---|
minimumCapacity | int: the minimum desired capacity. |
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
| Parameters |
|---|
srcBegin | int: start copying at this offset. |
srcEnd | int: stop copying at this offset. |
dst | char: the array to copy the data into. |
dstBegin | int: offset into dst. |
| Throws |
|---|
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 |
indexOf
public int indexOf (String str)
indexOf
public int indexOf (String str, int fromIndex)
| Parameters |
|---|
str | String |
fromIndex | int |
insert
public StringBuilder insert (int offset, char[] str)
| Parameters |
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offset | int |
str | char |
insert
public StringBuilder insert (int offset, float f)
| Parameters |
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offset | int |
f | float |
insert
public StringBuilder insert (int offset, char c)
| Parameters |
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offset | int |
c | char |
insert
public StringBuilder insert (int offset, long l)
| Parameters |
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offset | int |
l | long |
insert
public StringBuilder insert (int index, char[] str, int offset, int len)
| Parameters |
|---|
index | int |
str | char |
offset | int |
len | int |
insert
public StringBuilder insert (int offset, int i)
| Parameters |
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offset | int |
i | int |
insert
public StringBuilder insert (int offset, double d)
| Parameters |
|---|
offset | int |
d | double |
insert
public StringBuilder insert (int dstOffset, CharSequence s, int start, int end)
| Parameters |
|---|
dstOffset | int |
s | CharSequence |
start | int |
end | int |
insert
public StringBuilder insert (int offset, boolean b)
| Parameters |
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offset | int |
b | boolean |
lastIndexOf
public int lastIndexOf (String str, int fromIndex)
| Parameters |
|---|
str | String |
fromIndex | int |
lastIndexOf
public int lastIndexOf (String str)
length
public int length ()
Returns the length (character count).
| Returns |
|---|
int | the length of the sequence of characters currently represented by this object |
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.
| Parameters |
|---|
index | int: the index to be offset |
codePointOffset | int: the offset in code points |
| Returns |
|---|
int | the index within this sequence |
| Throws |
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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. |
replace
public StringBuilder replace (int start, int end, String str)
| Parameters |
|---|
start | int |
end | int |
str | String |
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.
| Parameters |
|---|
index | int: the index of the character to modify. |
ch | char: the new character. |
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.
| Parameters |
|---|
newLength | int: the new length |
subSequence
public CharSequence subSequence (int start, int end)
Returns a new character sequence that is a subsequence of this sequence.
An invocation of this method of the form
sb.subSequence(begin, 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 | int: the start index, inclusive. |
end | int: the end index, exclusive. |
| Throws |
|---|
IndexOutOfBoundsException | if start or end are negative, if end is greater than length(), or if start is greater than end |
substring
public String substring (int start, 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 | int: The beginning index, inclusive. |
end | int: The ending index, exclusive. |
| Returns |
|---|
String | The new string. |
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.
| Parameters |
|---|
start | int: The beginning index, inclusive. |
| Returns |
|---|
String | The new string. |
toString
public String toString ()
Returns a string representation of the object.
| Returns |
|---|
String | a string representation of the object. |
trimToSize
public void trimToSize ()
Attempts to reduce storage used for the character sequence. If the buffer is larger than necessary to hold its current sequence of characters, then it may be resized to become more space efficient. Calling this method may, but is not required to, affect the value returned by a subsequent call to the capacity() method.
