public final class StringBuilder
- Object
- StringBuilder
ImplementsCharSequence
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 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 builders are used by the compiler to implement the binary string concatenation operator +. For example, the code:
is compiled to the equivalent of:
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 builder array. If the internal builder overflows, it is automatically made larger.
Since: JDK1.0, CLDC 1.0 See Also:ByteArrayOutputStream, String
Constructors
public StringBuilder() | Constructs a string builder with no characters in it and an initial capacity of 16 characters. |
public StringBuilder(int length) | Constructs a string builder with no characters in it and an initial capacity specified by the length argument. |
public StringBuilder(String str) | 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. |
public StringBuilder(CharSequence cs) |
Methods
Inherited methods
Constructor details
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. length - the initial capacity.
- if the length argument is less than 0.
StringBuilder
public StringBuilder(String str)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.
str - the initial contents of the builder.
StringBuilder
public StringBuilder(CharSequence cs)Method details
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.
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.
append
public StringBuilder append(char[] str)append
public StringBuilder append(char[] str, 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.
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.
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.
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.
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.
append
public StringBuilder append(Object obj)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.
append
public StringBuilder append(String str)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.
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.
charAt
public char charAt(int index)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
indexint- the index of the character to return.
Returns
the requested character.
Throws
IndexOutOfBoundsException- if
index < 0orindexis greater than the length of this sequence.
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.
append
public StringBuilder append(StringBuffer buf)Appends StringBuffer to end of builder.
Parameters
bufStringBuffer- The string buffer to append
Returns
Self for chaining.
deleteCharAt
public StringBuilder deleteCharAt(int index)Removes the character at the specified position in this StringBuilder (shortening the StringBuilder by one character).
ensureCapacity
public void ensureCapacity(int minimumCapacity)Ensures that the capacity of the builder 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 builder 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.
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
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.
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.
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.
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.
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.
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.
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.
insert
public StringBuilder insert(int offset, String str)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 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 builder.
length
public int length()Returns the length (character count) of this string builder.
Returns
the number of characters.
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.
setCharAt
public void setCharAt(int index, char ch)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.
setLength
public void setLength(int newLength)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
less than newLength, the character at index
in the new character sequence is the same as the character at index
in the old sequence if
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.
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 builder 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.
trimToSize
public void trimToSize()append
public StringBuilder append(CharSequence cs)append
public StringBuilder append(CharSequence cs, int start, int end)insert
public StringBuilder insert(int offset, CharSequence cs)insert
public StringBuilder insert(int offset, CharSequence cs, int start, int end)subSequence
public CharSequence subSequence(int start, int end)Returns a
CharSequence from the start index (inclusive)
to the end index (exclusive) of this sequence.Parameters
startint- the start offset of the sub-sequence. It is inclusive, that is, the index of the first character that is included in the sub-sequence.
endint- the end offset of the sub-sequence. It is exclusive, that is, the index of the first character after those that are included in the sub-sequence
Returns
the requested sub-sequence.
Throws
IndexOutOfBoundsException- if
start end, or ifstartorendare greater than the length of this sequence.