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java.lang
Class StringBuffer
java.lang.Object
|
+--java.lang.StringBuffer
public final class StringBufferextends
ObjectA string buffer implements a mutable sequence of characters. A string buffer is like a String, but can be modified. At any point in time it contains some particular sequence of characters, but the length and content of the sequence can be changed through certain method calls.
String buffers are safe for use by multiple threads. The methods are synchronized where necessary so that all the operations on any particular instance behave as if they occur in some serial order that is consistent with the order of the method calls made by each of the individual threads involved.
String buffers are used by the compiler to implement the binary string concatenation operator +. For example, the code:
x = "a" + 4 + "c"
is compiled to the equivalent of:
x = new StringBuffer().append("a").append(4).append("c") .toString()which creates a new string buffer (initially empty), appends the string representation of each operand to the string buffer in turn, and then converts the contents of the string buffer to a string. Overall, this avoids creating many temporary strings.
The principal operations on a StringBuffer are the append and insert methods, which are overloaded so as to accept data of any type. Each effectively converts a given datum to a string and then appends or inserts the characters of that string to the string buffer. The append method always adds these characters at the end of the buffer; the insert method adds the characters at a specified point.
For example, if z refers to a string buffer object whose current contents are "start", then the method call z.append("le") would cause the string buffer to contain "startle", whereas z.insert(4, "le") would alter the string buffer to contain "starlet".
In general, if sb refers to an instance of a StringBuffer, then sb.append(x) has the same effect as sb.insert(sb.length(), x).
Every string buffer has a capacity. As long as the length of the character sequence contained in the string buffer does not exceed the capacity, it is not necessary to allocate a new internal buffer array. If the internal buffer overflows, it is automatically made larger.
Since: JDK1.0See Also: ByteArrayOutputStream, StringConstructor Summary |
StringBuffer() Constructs a string buffer with no characters in it and an initial capacity of 16 characters. |
StringBuffer(int length) Constructs a string buffer with no characters in it and an initial capacity specified by the length argument. |
StringBuffer(String str) Constructs a string buffer so that it represents the same sequence of characters as the string argument; in other words, the initial contents of the string buffer is a copy of the argument string. |
Method Summary | |
StringBuffer | append(boolean b) Appends the string representation of the boolean argument to the string buffer. |
StringBuffer | append(char c) Appends the string representation of the char argument to this string buffer. |
StringBuffer | append(char[] str) Appends the string representation of the char array argument to this string buffer. |
StringBuffer | append(char[] str,
int offset,
int len) Appends the string representation of a subarray of the char array argument to this string buffer. |
StringBuffer | append(int i) Appends the string representation of the int argument to this string buffer. |
StringBuffer | append(long l) Appends the string representation of the long argument to this string buffer. |
StringBuffer | append(Object obj) Appends the string representation of the Object argument to this string buffer. |
StringBuffer | append(String str) Appends the string to this string buffer. |
int | capacity() Returns the current capacity of the String buffer. |
char | charAt(int index) The specified character of the sequence currently represented by the string buffer, as indicated by the index argument, is returned. |
StringBuffer | delete(int start,
int end) Removes the characters in a substring of this StringBuffer. |
StringBuffer | deleteCharAt(int index) Removes the character at the specified position in this StringBuffer (shortening the StringBuffer by one character). |
void | ensureCapacity(int minimumCapacity) 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 buffer into the destination character array dst. |
StringBuffer | insert(int offset,
boolean b) Inserts the string representation of the boolean argument into this string buffer. |
StringBuffer | insert(int offset,
char c) Inserts the string representation of the char argument into this string buffer. |
StringBuffer | insert(int offset,
char[] str) Inserts the string representation of the char array argument into this string buffer. |
StringBuffer | insert(int offset,
int i) Inserts the string representation of the second int argument into this string buffer. |
StringBuffer | insert(int offset,
long l) Inserts the string representation of the long argument into this string buffer. |
StringBuffer | insert(int offset,
Object obj) Inserts the string representation of the Object argument into this string buffer. |
StringBuffer | insert(int offset,
String str) Inserts the string into this string buffer. |
int | length() Returns the length (character count) of this string buffer. |
StringBuffer | reverse() The character sequence contained in this string buffer is replaced by the reverse of the sequence. |
void | setCharAt(int index,
char ch) The character at the specified index of this string buffer is set to ch. |
void | setLength(int newLength) Sets the length of this String buffer. |
String | toString() Converts to a string representing the data in this string buffer. |
StringBuffer
public StringBuffer()Constructs a string buffer with no characters in it and an initial capacity of 16 characters.StringBuffer
public StringBuffer(int length)Constructs a string buffer with no characters in it and an initial capacity specified by the length argument.Parameters:length - the initial capacity.Throws:NegativeArraySizeException - if the length argument is less than 0.StringBuffer
public StringBuffer(String str)Constructs a string buffer so that it represents the same sequence of characters as the string argument; in other words, the initial contents of the string buffer is a copy of the argument string. The initial capacity of the string buffer is 16 plus the length of the string argument.Parameters:str - the initial contents of the buffer.length
public int length()Returns the length (character count) of this string buffer.Returns:the length of the sequence of characters currently represented by this string buffer.capacity
public int capacity()Returns the current capacity of the String buffer. The capacity is the amount of storage available for newly inserted characters; beyond which an allocation will occur.Returns:the current capacity of this string buffer.ensureCapacity
public void ensureCapacity(int minimumCapacity)Ensures that the capacity of the buffer is at least equal to the specified minimum. If the current capacity of this string buffer is less than the argument, then a new internal buffer is allocated with greater capacity. The new capacity is the larger of:- The minimumCapacity argument.
- Twice the old capacity, plus 2.