Class StringBuffer

java.lang.Object
java.lang.StringBuffer
All Implemented Interfaces:
Appendable, CharSequence, Comparable<StringBuffer>
public final class StringBuffer extends Object implements CharSequence, Appendable, Comparable<StringBuffer>
A 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: is compiled to the equivalent of: 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: JDK1.0, CLDC 1.0 See Also:ByteArrayOutputStream, String

  • Constructor Summary

    Constructors
    Constructor
    Description
    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(CharSequence cs)
    A StringBuffer holding the characters of cs.
    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

    Modifier and Type
    Method
    Description
    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)
     
    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(double d)
    Appends the string representation of the double argument to this string buffer.
    StringBuffer
    append(float f)
    Appends the string representation of the float 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(CharSequence cs)
    Appends the character sequence csq.
    StringBuffer
    append(CharSequence cs, int start, int end)
    Appends a subsequence of csq.
    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.
    StringBuffer
    append(StringBuffer sb)
    Appends the contents of sb, or "null".
    StringBuffer
    appendCodePoint(int codePoint)
    Appends the code point, as one char or as a surrogate pair.
    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.
    int
    codePointAt(int index)
    The code point at index.
    int
    codePointBefore(int index)
    The code point that ends just before index.
    int
    codePointCount(int beginIndex, int endIndex)
    The number of code points between beginIndex and endIndex.
    int
    compareTo(StringBuffer another)
    Compares the contents lexicographically.
    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.
    int
    indexOf(String str)
    The first index of str, or -1.
    int
    indexOf(String str, int fromIndex)
    The first index of str at or after fromIndex, or -1.
    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)
     
    StringBuffer
    insert(int index, char[] str, int offset, int len)
    Inserts len chars of str from offset at index.
    StringBuffer
    insert(int offset, double d)
    Inserts the string representation of the double argument into this string buffer.
    StringBuffer
    insert(int offset, float f)
    Inserts the string representation of the float 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, CharSequence cs)
     
    StringBuffer
    insert(int offset, CharSequence cs, int start, int end)
     
    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
    lastIndexOf(String str)
    The last index of str, or -1.
    int
    lastIndexOf(String str, int fromIndex)
    The last index of str at or before fromIndex, or -1.
    int
    length()
    Returns the length (character count) of this string buffer.
    int
    offsetByCodePoints(int index, int codePointOffset)
    The index codePointOffset code points away from index.
    StringBuffer
    repeat(int codePoint, int count)
    Appends the code point count times.
    StringBuffer
    repeat(CharSequence cs, int count)
    Appends cs count times.
    StringBuffer
    replace(int start, int end, String str)
    Replaces the characters from start to end with str.
    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.
    CharSequence
    subSequence(int start, int end)
    Returns a CharSequence from the start index (inclusive) to the end index (exclusive) of this sequence.
    String
    substring(int start)
    The characters from start to the end.
    String
    substring(int start, int end)
    The characters from start to end.
    String
    toString()
    Converts to a string representing the data in this string buffer.
    void
    trimToSize()
     

    Methods inherited from class Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

    Methods inherited from interface CharSequence

    chars, codePoints, isEmpty

  • Constructor Details

    • 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. length - the initial capacity.

      • 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. str - the initial contents of the buffer.

    • StringBuffer

      public StringBuffer(CharSequence cs)
      A StringBuffer holding the characters of cs.

  • Method Details

    • append

      public StringBuffer append(boolean b)
      Appends the string representation of the boolean argument to the string buffer. 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 buffer.

    • append

      public StringBuffer append(char c)
      Appends the string representation of the char argument to this string buffer. The argument is appended to the contents of this string buffer. The length of this string buffer 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 StringBuffer object.
      Specified by:
      append in interface Appendable

    • append

      public StringBuffer append(char[] str)

    • append

      public StringBuffer append(char[] str, int offset, int len)
      Appends the string representation of a subarray of the char array argument to this string buffer. Characters of the character array str, starting at index offset, are appended, in order, to the contents of this string buffer. The length of this string buffer 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 StringBuffer object.

    • append

      public StringBuffer append(double d)
      Appends the string representation of the double argument to this string buffer. 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 buffer.

    • append

      public StringBuffer append(float f)
      Appends the string representation of the float argument to this string buffer. 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 buffer.

    • append

      public StringBuffer append(int i)
      Appends the string representation of the int argument to this string buffer. 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 buffer.

    • append

      public StringBuffer append(long l)
      Appends the string representation of the long argument to this string buffer. 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 buffer.

    • append

      public StringBuffer append(Object obj)
      Appends the string representation of the Object argument to this string buffer. 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 buffer.

    • append

      public StringBuffer append(String str)
      Appends the string to this string buffer. The characters of the String argument are appended, in order, to the contents of this string buffer, increasing the length of this string buffer by the length of the argument. If str is null, then the four characters "null" are appended to this string buffer. Let n be the length of the old character sequence, the one contained in the string buffer 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 buffer. 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 buffer, as indicated by the index argument, is returned. The first character of a string buffer 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 buffer.
      Specified by:
      charAt in interface CharSequence

    • delete

      public StringBuffer delete(int start, int end)
      Removes the characters in a substring of this StringBuffer. The substring begins at the specified start and extends to the character at index end - 1 or to the end of the StringBuffer if no such character exists. If start is equal to end, no changes are made.

    • deleteCharAt

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

    • 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. 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 buffer 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 StringBuffer insert(int offset, boolean b)
      Inserts the string representation of the boolean argument into this string buffer. 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 buffer 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 buffer.

    • insert

      public StringBuffer insert(int offset, char c)
      Inserts the string representation of the char argument into this string buffer. The second argument is inserted into the contents of this string buffer at the position indicated by offset. The length of this string buffer 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 StringBuffer 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 buffer.

    • insert

      public StringBuffer insert(int offset, char[] str)

    • insert

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

    • insert

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

    • insert

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

    • insert

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

    • insert

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

    • insert

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

    • length

      public int length()
      Returns the length (character count) of this string buffer.
      Specified by:
      length in interface CharSequence

    • reverse

      public StringBuffer reverse()
      The character sequence contained in this string buffer is replaced by the reverse of the sequence. Let n be the length of the old character sequence, the one contained in the string buffer 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 buffer is set to ch. The string buffer 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 buffer.

    • setLength

      public void setLength(int newLength)
      Sets the length of this string buffer. This string buffer 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 buffer, the string buffer 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 buffer 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 buffer. A new String object is allocated and initialized to contain the character sequence currently represented by this string buffer. This String is then returned. Subsequent changes to the string buffer 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 buffer. Any subsequent operation that alters the content or capacity of the string buffer 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 buffer.
      Specified by:
      toString in interface CharSequence
      Overrides:
      toString in class Object

    • trimToSize

      public void trimToSize()

    • append

      public StringBuffer append(CharSequence cs)
      Description copied from interface: Appendable

      Appends the character sequence csq. Implementation classes may not append the whole sequence, for example if the target is a buffer with limited size.

      If csq is null, the characters "null" are appended.

      Parameters
      • csq: the character sequence to append.
      Returns

      this Appendable.

      Throws
      • IOException: if an I/O error occurs.
      Specified by:
      append in interface Appendable

    • append

      public StringBuffer append(CharSequence cs, int start, int end)
      Description copied from interface: Appendable

      Appends a subsequence of csq.

      If csq is not null then calling this method is equivalent to calling append(csq.subSequence(start, end)).

      If csq is null, the characters "null" are appended.

      Parameters

      • csq: the character sequence to append.

      • start: @param start the first index of the subsequence of csq that is appended.

      • end: @param end the last index of the subsequence of csq that is appended.

      Returns

      this Appendable.

      Throws

      • IndexOutOfBoundsException: @throws IndexOutOfBoundsException if start end or end is greater than the length of csq.

      • IOException: if an I/O error occurs.

      Specified by:
      append in interface Appendable

    • insert

      public StringBuffer insert(int offset, CharSequence cs)

    • insert

      public StringBuffer insert(int offset, CharSequence cs, int start, int end)

    • subSequence

      public CharSequence subSequence(int start, int end)
      Description copied from interface: CharSequence

      Returns a CharSequence from the start index (inclusive) to the end index (exclusive) of this sequence.

      Parameters

      • start: @param start 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.

      • end: @param end 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: @throws IndexOutOfBoundsException if start end, or if start or end are greater than the length of this sequence.
      Specified by:
      subSequence in interface CharSequence

    • append

      public StringBuffer append(StringBuffer sb)
      Appends the contents of sb, or "null".

    • insert

      public StringBuffer insert(int index, char[] str, int offset, int len)
      Inserts len chars of str from offset at index.

    • appendCodePoint

      public StringBuffer appendCodePoint(int codePoint)
      Appends the code point, as one char or as a surrogate pair.

    • codePointAt

      public int codePointAt(int index)
      The code point at index.

    • codePointBefore

      public int codePointBefore(int index)
      The code point that ends just before index.

    • codePointCount

      public int codePointCount(int beginIndex, int endIndex)
      The number of code points between beginIndex and endIndex.

    • offsetByCodePoints

      public int offsetByCodePoints(int index, int codePointOffset)
      The index codePointOffset code points away from index.

    • indexOf

      public int indexOf(String str)
      The first index of str, or -1.

    • indexOf

      public int indexOf(String str, int fromIndex)
      The first index of str at or after fromIndex, or -1.

    • lastIndexOf

      public int lastIndexOf(String str)
      The last index of str, or -1.

    • lastIndexOf

      public int lastIndexOf(String str, int fromIndex)
      The last index of str at or before fromIndex, or -1.

    • replace

      public StringBuffer replace(int start, int end, String str)
      Replaces the characters from start to end with str.

    • substring

      public String substring(int start)
      The characters from start to the end.

    • substring

      public String substring(int start, int end)
      The characters from start to end.

    • repeat

      public StringBuffer repeat(int codePoint, int count)
      Appends the code point count times.

    • repeat

      public StringBuffer repeat(CharSequence cs, int count)
      Appends cs count times.

    • compareTo

      public int compareTo(StringBuffer another)
      Compares the contents lexicographically.
      Specified by:
      compareTo in interface Comparable<StringBuffer>
      Returns:

      a negative integer if this instance is less than another; a positive integer if this instance is greater than another; 0 if this instance has the same order as another.

      Throws
      • ClassCastException: @throws ClassCastException if another cannot be converted into something comparable to this instance.