FileDocCategorySizeDatePackage
StringBuffer.javaAPI DocphoneME MR2 API (J2ME)40265Wed May 02 17:59:56 BST 2007java.lang

StringBuffer

public final class StringBuffer extends Object
A string buffer implements a mutable sequence of characters. A string buffer is like a {@link 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.

version
12/17/01 (CLDC 1.1)
see
java.io.ByteArrayOutputStream
see
java.lang.String
since
JDK1.0, CLDC 1.0

Fields Summary
private char[]
value
The value is used for character storage.
private int
count
The count is the number of characters in the buffer.
private boolean
shared
A flag indicating whether the buffer is shared
Constructors Summary
public StringBuffer()
Constructs a string buffer with no characters in it and an initial capacity of 16 characters.

        value = new char[16];
    
public StringBuffer(int length)
Constructs a string buffer with no characters in it and an initial capacity specified by the length argument.

param
length the initial capacity.
exception
NegativeArraySizeException if the length argument is less than 0.

        value = new char[length];
    
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.

param
str the initial contents of the buffer.

        this(str.length() + 16);
        append(str);
    
Methods Summary
public synchronized java.lang.StringBufferappend(java.lang.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.

param
obj an Object.
return
a reference to this StringBuffer object.
see
java.lang.String#valueOf(java.lang.Object)
see
java.lang.StringBuffer#append(java.lang.String)

        return append(String.valueOf(obj));
    
public synchronized java.lang.StringBufferappend(java.lang.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.

param
str a string.
return
a reference to this StringBuffer.

          if (str == null) {
              str = String.valueOf(str);
          }
  
          int len = str.length();
          int newcount = count + len;
          if (newcount > value.length)
              expandCapacity(newcount);
          str.getChars(0, len, value, count);
          count = newcount;
          return this;
      
public synchronized java.lang.StringBufferappend(char[] str)
Appends the string representation of the char array argument to this string buffer.

The characters of the array argument are appended, in order, to the contents of this string buffer. 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 {@link String#valueOf(char[])} and the characters of that string were then {@link #append(String) appended} to this StringBuffer object.

param
str the characters to be appended.
return
a reference to this StringBuffer object.

        int len = str.length;
        int newcount = count + len;
        if (newcount > value.length)
            expandCapacity(newcount);
        JVM.unchecked_char_arraycopy(str, 0, value, count, len);
        count = newcount;
        return this;
    
public synchronized java.lang.StringBufferappend(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 {@link String#valueOf(char[],int,int)} and the characters of that string were then {@link #append(String) appended} to this StringBuffer object.

param
str the characters to be appended.
param
offset the index of the first character to append.
param
len the number of characters to append.
return
a reference to this StringBuffer object.

        int newcount = count + len;
        if (newcount > value.length)
            expandCapacity(newcount);
        // NOTE: str and offset not checked, cannot use unchecked arraycopy
        System.arraycopy(str, offset, value, count, len);
        count = newcount;
        return this;
    
public java.lang.StringBufferappend(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.

param
b a boolean.
return
a reference to this StringBuffer.
see
java.lang.String#valueOf(boolean)
see
java.lang.StringBuffer#append(java.lang.String)

        return append(String.valueOf(b));
    
public synchronized java.lang.StringBufferappend(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 {@link String#valueOf(char)} and the character in that string were then {@link #append(String) appended} to this StringBuffer object.

param
c a char.
return
a reference to this StringBuffer object.

        int newcount = count + 1;
        if (newcount > value.length)
            expandCapacity(newcount);
        value[count++] = c;
        return this;
    
public java.lang.StringBufferappend(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.

param
i an int.
return
a reference to this StringBuffer object.
see
java.lang.String#valueOf(int)
see
java.lang.StringBuffer#append(java.lang.String)

        return append(String.valueOf(i));
    
public java.lang.StringBufferappend(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.

param
l a long.
return
a reference to this StringBuffer object.
see
java.lang.String#valueOf(long)
see
java.lang.StringBuffer#append(java.lang.String)

        return append(String.valueOf(l));
    
public java.lang.StringBufferappend(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.

param
f a float.
return
a reference to this StringBuffer object.
see
java.lang.String#valueOf(float)
see
java.lang.StringBuffer#append(java.lang.String)
since
CLDC 1.1

        return append(String.valueOf(f));
    
public java.lang.StringBufferappend(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.

param
d a double.
return
a reference to this StringBuffer object.
see
java.lang.String#valueOf(double)
see
java.lang.StringBuffer#append(java.lang.String)
since
CLDC 1.1

        return append(String.valueOf(d));
    
public intcapacity()
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.

return
the current capacity of this string buffer.

        return value.length;
    
public synchronized charcharAt(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.

param
index the index of the desired character.
return
the character at the specified index of this string buffer.
exception
IndexOutOfBoundsException if index is negative or greater than or equal to length().
see
java.lang.StringBuffer#length()

        if ((index < 0) || (index >= count)) {
            throw new StringIndexOutOfBoundsException(
/* #ifdef VERBOSE_EXCEPTIONS */
/// skipped                       index
/* #endif */
            );
        }
        return value[index];
    
private final voidcopy()
Copies the buffer value. This is normally only called when shared is true. It should only be called from a synchronized method.

        char newValue[] = new char[value.length];
        JVM.unchecked_char_arraycopy(value, 0, newValue, 0, count);
        value = newValue;
        shared = false;
    
public synchronized java.lang.StringBufferdelete(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.

param
start The beginning index, inclusive.
param
end The ending index, exclusive.
return
This string buffer.
exception
StringIndexOutOfBoundsException if start is negative, greater than length(), or greater than end.
since
JDK1.2

        if (start < 0)
            throw new StringIndexOutOfBoundsException(
/* #ifdef VERBOSE_EXCEPTIONS */
/// skipped                       start
/* #endif */
            );
        if (end > count)
            end = count;
        if (start > end)
            throw new StringIndexOutOfBoundsException();

        int len = end - start;
        if (len > 0) {
            if (shared)
                copy();
            JVM.unchecked_char_arraycopy(value, start+len, 
                                         value, start, count-end);
            count -= len;
        }
        return this;
    
public synchronized java.lang.StringBufferdeleteCharAt(int index)
Removes the character at the specified position in this StringBuffer (shortening the StringBuffer by one character).

param
index Index of character to remove
return
This string buffer.
exception
StringIndexOutOfBoundsException if the index is negative or greater than or equal to length().
since
JDK1.2

        if ((index < 0) || (index >= count))
            throw new StringIndexOutOfBoundsException();
        if (shared)
            copy();
        JVM.unchecked_char_arraycopy(value, index+1, 
                                     value, index, count-index-1);
        count--;
        return this;
    
public synchronized voidensureCapacity(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.

param
minimumCapacity the minimum desired capacity.

        if (minimumCapacity > value.length) {
            expandCapacity(minimumCapacity);
        }
    
private voidexpandCapacity(int minimumCapacity)
This implements the expansion semantics of ensureCapacity but is unsynchronized for use internally by methods which are already synchronized.

see
java.lang.StringBuffer#ensureCapacity(int)

        int newCapacity = (value.length + 1) * 2;
        if (newCapacity < 0) {
            newCapacity = Integer.MAX_VALUE;
        } else if (minimumCapacity > newCapacity) {
            newCapacity = minimumCapacity;
        }
        
        char newValue[] = new char[newCapacity];
        JVM.unchecked_char_arraycopy(value, 0, newValue, 0, count);
        value = newValue;
        shared = false;
    
public synchronized voidgetChars(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

param
srcBegin start copying at this offset in the string buffer.
param
srcEnd stop copying at this offset in the string buffer.
param
dst the array to copy the data into.
param
dstBegin offset into dst.
exception
NullPointerException if dst is null.
exception
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 buffer.
  • dstBegin+srcEnd-srcBegin is greater than dst.length

        if (srcBegin < 0) {
            throw new StringIndexOutOfBoundsException(
/* #ifdef VERBOSE_EXCEPTIONS */
/// skipped                       srcBegin
/* #endif */
            );
        }
        if ((srcEnd < 0) || (srcEnd > count)) {
            throw new StringIndexOutOfBoundsException(
/* #ifdef VERBOSE_EXCEPTIONS */
/// skipped                       srcEnd
/* #endif */
            );
        }
        if (srcBegin > srcEnd) {
            throw new StringIndexOutOfBoundsException(
/* #ifdef VERBOSE_EXCEPTIONS */
/// skipped                       "srcBegin > srcEnd"
/* #endif */
            );
        }
        // NOTE: dst not checked, cannot use unchecked arraycopy
        System.arraycopy(value, srcBegin, dst, dstBegin, srcEnd - srcBegin);
    
final char[]getValue()

 return value; 
public synchronized java.lang.StringBufferinsert(int offset, java.lang.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.

param
offset the offset.
param
obj an Object.
return
a reference to this StringBuffer object.
exception
StringIndexOutOfBoundsException if the offset is invalid.
see
java.lang.String#valueOf(java.lang.Object)
see
java.lang.StringBuffer#insert(int, java.lang.String)
see
java.lang.StringBuffer#length()

        return insert(offset, String.valueOf(obj));
    
public synchronized java.lang.StringBufferinsert(int offset, java.lang.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.

param
offset the offset.
param
str a string.
return
a reference to this StringBuffer object.
exception
StringIndexOutOfBoundsException if the offset is invalid.
see
java.lang.StringBuffer#length()

        if ((offset < 0) || (offset > count)) {
            throw new StringIndexOutOfBoundsException();
        }

        if (str == null) {
            str = String.valueOf(str);
        }
        int len = str.length();
        int newcount = count + len;
        if (newcount > value.length)
            expandCapacity(newcount);
        else if (shared)
            copy();
        JVM.unchecked_char_arraycopy(value, offset, 
                                     value, offset + len, count - offset);
        str.getChars(0, len, value, offset);
        count = newcount;
        return this;
    
public synchronized java.lang.StringBufferinsert(int offset, char[] str)
Inserts the string representation of the char array argument into this string buffer.

The characters of the array argument are inserted into the contents of this string buffer at the position indicated by offset. 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 {@link String#valueOf(char[])} and the characters of that string were then {@link #insert(int,String) inserted} into this StringBuffer object at the position indicated by offset.

param
offset the offset.
param
str a character array.
return
a reference to this StringBuffer object.
exception
StringIndexOutOfBoundsException if the offset is invalid.

        if ((offset < 0) || (offset > count)) {
            throw new StringIndexOutOfBoundsException();
        }
        int len = str.length;
        int newcount = count + len;
        if (newcount > value.length)
            expandCapacity(newcount);
        else if (shared)
            copy();
        JVM.unchecked_char_arraycopy(value, offset, 
                                     value, offset + len, count - offset);
        JVM.unchecked_char_arraycopy(str, 0, value, offset, len);
        count = newcount;
        return this;
    
public java.lang.StringBufferinsert(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.

param
offset the offset.
param
b a boolean.
return
a reference to this StringBuffer object.
exception
StringIndexOutOfBoundsException if the offset is invalid.
see
java.lang.String#valueOf(boolean)
see
java.lang.StringBuffer#insert(int, java.lang.String)
see
java.lang.StringBuffer#length()

        return insert(offset, String.valueOf(b));
    
public synchronized java.lang.StringBufferinsert(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 {@link String#valueOf(char)} and the character in that string were then {@link #insert(int, String) 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.

param
offset the offset.
param
c a char.
return
a reference to this StringBuffer object.
exception
IndexOutOfBoundsException if the offset is invalid.
see
java.lang.StringBuffer#length()

        int newcount = count + 1;
        if (newcount > value.length)
            expandCapacity(newcount);
        else if (shared)
            copy();
        // NOTE: offset not checked, cannot use unchecked arraycopy
        System.arraycopy(value, offset, value, offset + 1, count - offset);
        value[offset] = c;
        count = newcount;
        return this;
    
public java.lang.StringBufferinsert(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.

param
offset the offset.
param
i an int.
return
a reference to this StringBuffer object.
exception
StringIndexOutOfBoundsException if the offset is invalid.
see
java.lang.String#valueOf(int)
see
java.lang.StringBuffer#insert(int, java.lang.String)
see
java.lang.StringBuffer#length()

        return insert(offset, String.valueOf(i));
    
public java.lang.StringBufferinsert(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.

param
offset the offset.
param
l a long.
return
a reference to this StringBuffer object.
exception
StringIndexOutOfBoundsException if the offset is invalid.
see
java.lang.String#valueOf(long)
see
java.lang.StringBuffer#insert(int, java.lang.String)
see
java.lang.StringBuffer#length()

        return insert(offset, String.valueOf(l));
    
public java.lang.StringBufferinsert(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.

param
offset the offset.
param
f a float.
return
a reference to this StringBuffer object.
exception
StringIndexOutOfBoundsException if the offset is invalid.
see
java.lang.String#valueOf(float)
see
java.lang.StringBuffer#insert(int, java.lang.String)
see
java.lang.StringBuffer#length()
since
CLDC 1.1

        return insert(offset, String.valueOf(f));
    
public java.lang.StringBufferinsert(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.

param
offset the offset.
param
d a double.
return
a reference to this StringBuffer object.
exception
StringIndexOutOfBoundsException if the offset is invalid.
see
java.lang.String#valueOf(double)
see
java.lang.StringBuffer#insert(int, java.lang.String)
see
java.lang.StringBuffer#length()
since
CLDC 1.1

        return insert(offset, String.valueOf(d));
    
public intlength()
Returns the length (character count) of this string buffer.

return
the length of the sequence of characters currently represented by this string buffer.

        return count;
    
public synchronized java.lang.StringBufferreverse()
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.

return
a reference to this StringBuffer object..
since
JDK1.0.2

        if (shared) copy();
        int n = count - 1;
        for (int j = (n-1) >> 1; j >= 0; --j) {
            char temp = value[j];
            value[j] = value[n - j];
            value[n - j] = temp;
        }
        return this;
    
public synchronized voidsetCharAt(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.

param
index the index of the character to modify.
param
ch the new character.
exception
IndexOutOfBoundsException if index is negative or greater than or equal to length().
see
java.lang.StringBuffer#length()

        if ((index < 0) || (index >= count)) {
            throw new StringIndexOutOfBoundsException(
/* #ifdef VERBOSE_EXCEPTIONS */
/// skipped                       index
/* #endif */
            );
        }
        if (shared) copy();
        value[index] = ch;
    
public synchronized voidsetLength(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 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 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.

param
newLength the new length of the buffer.
exception
IndexOutOfBoundsException if the newLength argument is negative.
see
java.lang.StringBuffer#length()

        if (newLength < 0) {
            throw new StringIndexOutOfBoundsException(
/* #ifdef VERBOSE_EXCEPTIONS */
/// skipped                       newLength
/* #endif */
            );
        }
        
        if (newLength > value.length) {
            expandCapacity(newLength);
        }

        if (count < newLength) {
            if (shared) copy();
            for (; count < newLength; count++) {
                value[count] = '\0";
            }
        } else {
            count = newLength;
            if (shared) {
                if (newLength > 0) {
                    copy();
                } else {
                    // If newLength is zero, assume the StringBuffer is being
                    // stripped for reuse; Make new buffer of default size
                    value = new char[16];
                    shared = false;
                }
            }
        }
    
final voidsetShared()

 shared = true; 
public java.lang.StringtoString()
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.

return
a string representation of the string buffer.

        return new String(this);