java.lang
Class StringBuilder

java.lang.Object
  extended by java.lang.StringBuilder

public final class StringBuilder
extends Object

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. A string builder implements a mutable sequence of characters. A string builder 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 builders 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 StringBuilder().append("a").append(4).append("c")
                           .toString()
 
which creates a new string builder (initially empty), appends the string representation of each operand to the string builder in turn, and then converts the contents of the string builder to a string. Overall, this avoids creating many temporary strings.

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 array. If the internal buffer overflows, it is automatically made larger.

Since:
JDK1.0, CLDC 1.0
Version:
1/1/08 (CLDC 1.1)
See Also:
ByteArrayOutputStream, String, StringBuffer

Constructor Summary
StringBuilder()
          Constructs a string builder with no characters in it and an initial capacity of 16 characters.
StringBuilder(int length)
          Constructs a string builder with no characters in it and an initial capacity specified by the length argument.
StringBuilder(String s)
          Constructs a string builder so that it represents the same sequence of characters as the string argument; in other words, the initial contents of the string builder is a copy of the argument string.
 
Method Summary
 StringBuilder append(boolean b)
          Appends the string representation of the boolean argument to the string builder.
 StringBuilder append(char c)
          Appends the string representation of the char argument to this string builder.
 StringBuilder append(char[] chars)
          Appends the string representation of the char array argument to this string builder.
 StringBuilder append(char[] chars, int offset, int len)
          Appends the string representation of a subarray of the char array argument to this string builder.
 StringBuilder append(double d)
          Appends the string representation of the double argument to this string builder.
 StringBuilder append(float f)
          Appends the string representation of the float argument to this string builder.
 StringBuilder append(int i)
          Appends the string representation of the int argument to this string builder.
 StringBuilder append(long l)
          Appends the string representation of the long argument to this string builder.
 StringBuilder append(Object aObject)
          Appends the string representation of the Object argument to this string builder.
 StringBuilder append(String s)
          Appends the string to this string builder.
 int capacity()
          Returns the current capacity of the string builder.
 char charAt(int i)
          The specified character of the sequence currently represented by the string builder, as indicated by the index argument, is returned.
 StringBuilder delete(int start, int end)
          Removes the characters in a substring of this StringBuilder.
 StringBuilder deleteCharAt(int index)
          Removes the character at the specified position in this StringBuilder (shortening the StringBuilder by one character).
 void ensureCapacity(int capacity)
          Ensures that the capacity of the buffer is at least equal to the specified minimum.
 void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
          Characters are copied from this string builder into the destination character array dst.
 StringBuilder insert(int offset, boolean b)
          Inserts the string representation of the boolean argument into this string builder.
 StringBuilder insert(int offset, char c)
          Inserts the string representation of the char argument into this string builder.
 StringBuilder insert(int offset, char[] chars)
          Inserts the string representation of the char array argument into this string builder.
 StringBuilder insert(int offset, double d)
          Inserts the string representation of the double argument into this string builder.
 StringBuilder insert(int offset, float f)
          Inserts the string representation of the float argument into this string builder.
 StringBuilder insert(int offset, int i)
          Inserts the string representation of the second int argument into this string builder.
 StringBuilder insert(int offset, long l)
          Inserts the string representation of the long argument into this string builder.
 StringBuilder insert(int offset, Object obj)
          Inserts the string representation of the Object argument into this string builder.
 StringBuilder insert(int offset, String s)
          Inserts the string into this string builder.
 int length()
          Returns the length (character count) of this string builder.
 StringBuilder reverse()
          The character sequence contained in this string builder is replaced by the reverse of the sequence.
 void setCharAt(int index, char c)
          The character at the specified index of this string builder is set to ch.
 void setLength(int length)
          Sets the length of this string builder.
 String toString()
          Converts to a string representing the data in this string builder.
 
Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Constructor Detail

StringBuilder

public StringBuilder()
Constructs a string builder with no characters in it and an initial capacity of 16 characters.


StringBuilder

public StringBuilder(int length)
Constructs a string builder 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.

StringBuilder

public StringBuilder(String s)
Constructs a string builder so that it represents the same sequence of characters as the string argument; in other words, the initial contents of the string builder is a copy of the argument string. The initial capacity of the string builder is 16 plus the length of the string argument.

Parameters:
s - the initial contents of the builder.
Method Detail

length

public int length()
Returns the length (character count) of this string builder.

Returns:
the length of the sequence of characters currently represented by this string builder.

capacity

public int capacity()
Returns the current capacity of the string builder. 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 builder.

ensureCapacity

public void ensureCapacity(int capacity)
Ensures that the capacity of the buffer is at least equal to the specified minimum. If the current capacity of this string builder is less than the argument, then a new internal buffer is allocated with greater capacity. The new capacity is the larger of: If the minimumCapacity argument is nonpositive, this method takes no action and simply returns.

Parameters:
capacity - the minimum desired capacity.

setLength

public void setLength(int length)
Sets the length of this string builder. This string builder 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 builder, the string builder 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 builder so that length becomes the newLength argument.

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

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

charAt

public char charAt(int i)
The specified character of the sequence currently represented by the string builder, as indicated by the index argument, is returned. The first character of a string builder 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 builder.

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

setCharAt

public void setCharAt(int index,
                      char c)
The character at the specified index of this string builder is set to ch. The string builder 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 builder.

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

getChars

public void getChars(int srcBegin,
                     int srcEnd,
                     char[] dst,
                     int dstBegin)
Characters are copied from this string builder 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 builder.
srcEnd - stop copying at this offset in the string builder.
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 builder.
  • dstBegin+srcEnd-srcBegin is greater than dst.length

insert

public StringBuilder insert(int offset,
                            String s)
Inserts the string into this string builder.

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

The character at index k in the new character sequence is equal to:

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

Parameters:
offset - the offset.
s - a string.
Returns:
a reference to this StringBuilder object.
Throws:
StringIndexOutOfBoundsException - if the offset is invalid.
See Also:
length()

insert

public StringBuilder insert(int offset,
                            Object obj)
Inserts the string representation of the Object argument into this string builder.

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 builder 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 builder.

Parameters:
offset - the offset.
obj - an Object.
Returns:
a reference to this StringBuilder object.
Throws:
StringIndexOutOfBoundsException - if the offset is invalid.
See Also:
String.valueOf(java.lang.Object), insert(int, java.lang.String), length()

insert

public StringBuilder insert(int offset,
                            char[] chars)
Inserts the string representation of the char array argument into this string builder.

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

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

Parameters:
offset - the offset.
chars - a character array.
Returns:
a reference to this StringBuilder object.
Throws:
StringIndexOutOfBoundsException - if the offset is invalid.

insert

public StringBuilder insert(int offset,
                            boolean b)
Inserts the string representation of the boolean argument into this string builder.

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 builder 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 builder.

Parameters:
offset - the offset.
b - a boolean.
Returns:
a reference to this StringBuilder object.
Throws:
StringIndexOutOfBoundsException - if the offset is invalid.
See Also:
String.valueOf(boolean), insert(int, java.lang.String), length()

insert

public StringBuilder insert(int offset,
                            char c)
Inserts the string representation of the char argument into this string builder.

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

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

Parameters:
offset - the offset.
c - a char.
Returns:
a reference to this StringBuilder object.
Throws:
IndexOutOfBoundsException - if the offset is invalid.
See Also:
length()

insert

public StringBuilder insert(int offset,
                            int i)
Inserts the string representation of the second int argument into this string builder.

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 builder 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 builder.

Parameters:
offset - the offset.
i - an int.
Returns:
a reference to this StringBuilder object.
Throws:
StringIndexOutOfBoundsException - if the offset is invalid.
See Also:
String.valueOf(int), insert(int, java.lang.String), length()

insert

public StringBuilder insert(int offset,
                            long l)
Inserts the string representation of the long argument into this string builder.

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 builder 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 builder.

Parameters:
offset - the offset.
l - a long.
Returns:
a reference to this StringBuilder object.
Throws:
StringIndexOutOfBoundsException - if the offset is invalid.
See Also:
String.valueOf(long), insert(int, java.lang.String), length()

insert

public StringBuilder insert(int offset,
                            float f)
Inserts the string representation of the float argument into this string builder.

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 builder 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 builder.

Parameters:
offset - the offset.
f - a float.
Returns:
a reference to this StringBuilder object.
Throws:
StringIndexOutOfBoundsException - if the offset is invalid.
Since:
CLDC 1.1
See Also:
String.valueOf(float), insert(int, java.lang.String), length()

insert

public StringBuilder insert(int offset,
                            double d)
Inserts the string representation of the double argument into this string builder.

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 builder 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 builder.

Parameters:
offset - the offset.
d - a double.
Returns:
a reference to this StringBuilder object.
Throws:
StringIndexOutOfBoundsException - if the offset is invalid.
Since:
CLDC 1.1
See Also:
String.valueOf(double), insert(int, java.lang.String), length()

append

public StringBuilder append(String s)
Appends the string to this string builder.

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

Let n be the length of the old character sequence, the one contained in the string builder 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:
s - a string.
Returns:
a reference to this StringBuilder.

append

public StringBuilder append(Object aObject)
Appends the string representation of the Object argument to this string builder.

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 builder.

Parameters:
aObject - an Object.
Returns:
a reference to this StringBuilder object.
See Also:
String.valueOf(java.lang.Object), append(java.lang.String)

append

public StringBuilder append(char[] chars,
                            int offset,
                            int len)
Appends the string representation of a subarray of the char array argument to this string builder.

Characters of the character array str, starting at index offset, are appended, in order, to the contents of this string builder. The length of this string builder 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 StringBuilder object.

Parameters:
chars - 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 StringBuilder object.

append

public StringBuilder append(char[] chars)
Appends the string representation of the char array argument to this string builder.

The characters of the array argument are appended, in order, to the contents of this string builder. 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 String.valueOf(char[]) and the characters of that string were then appended to this StringBuilder object.

Parameters:
chars - the characters to be appended.
Returns:
a reference to this StringBuilder object.

append

public StringBuilder append(boolean b)
Appends the string representation of the boolean argument to the string builder.

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 builder.

Parameters:
b - a boolean.
Returns:
a reference to this StringBuilder.
See Also:
String.valueOf(boolean), append(java.lang.String)

append

public StringBuilder append(char c)
Appends the string representation of the char argument to this string builder.

The argument is appended to the contents of this string builder. The length of this string builder 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 StringBuilder object.

Parameters:
c - a char.
Returns:
a reference to this StringBuilder object.

append

public StringBuilder append(int i)
Appends the string representation of the int argument to this string builder.

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 builder.

Parameters:
i - an int.
Returns:
a reference to this StringBuilder object.
See Also:
String.valueOf(int), append(java.lang.String)

append

public StringBuilder append(long l)
Appends the string representation of the long argument to this string builder.

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 builder.

Parameters:
l - a long.
Returns:
a reference to this StringBuilder object.
See Also:
String.valueOf(long), append(java.lang.String)

append

public StringBuilder append(double d)
Appends the string representation of the double argument to this string builder.

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 builder.

Parameters:
d - a double.
Returns:
a reference to this StringBuilder object.
Since:
CLDC 1.1
See Also:
String.valueOf(double), append(java.lang.String)

append

public StringBuilder append(float f)
Appends the string representation of the float argument to this string builder.

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 builder.

Parameters:
f - a float.
Returns:
a reference to this StringBuilder object.
Since:
CLDC 1.1
See Also:
String.valueOf(float), append(java.lang.String)

delete

public StringBuilder delete(int start,
                            int end)
Removes the characters in a substring of this StringBuilder. The substring begins at the specified start and extends to the character at index end - 1 or to the end of the StringBuilder 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 builder.
Throws:
StringIndexOutOfBoundsException - if start is negative, greater than length(), or greater than end.
Since:
JDK1.2

deleteCharAt

public StringBuilder deleteCharAt(int index)
Removes the character at the specified position in this StringBuilder (shortening the StringBuilder by one character).

Parameters:
index - Index of character to remove
Returns:
This string builder.
Throws:
StringIndexOutOfBoundsException - if the index is negative or greater than or equal to length().
Since:
JDK1.2

reverse

public StringBuilder reverse()
The character sequence contained in this string builder is replaced by the reverse of the sequence.

Let n be the length of the old character sequence, the one contained in the string builder 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 StringBuilder object..
Since:
JDK1.0.2

toString

public String toString()
Converts to a string representing the data in this string builder. A new String object is allocated and initialized to contain the character sequence currently represented by this string builder. This String is then returned. Subsequent changes to the string builder 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 builder. Any subsequent operation that alters the content or capacity of the string builder 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 builder.

Overrides:
toString in class Object
Returns:
a string representation of the string builder.


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