/*
 * @(#)StringBuffer.java	1.70 01/12/03
 *
 * Copyright 2002 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.lang;

/**
 * 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.
 * <p>
 * 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. 
 * <p>
 * String buffers are used by the compiler to implement the binary 
 * string concatenation operator <code>+</code>. For example, the code:
 * <p><blockquote><pre>
 *     x = "a" + 4 + "c"
 * </pre></blockquote><p>
 * is compiled to the equivalent of: 
 * <p><blockquote><pre>
 *     x = new StringBuffer().append("a").append(4).append("c")
 *                           .toString()
 * </pre></blockquote>
 * 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.
 * <p>
 * The principal operations on a <code>StringBuffer</code> are the 
 * <code>append</code> and <code>insert</code> 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 
 * <code>append</code> method always adds these characters at the end 
 * of the buffer; the <code>insert</code> method adds the characters at 
 * a specified point. 
 * <p>
 * For example, if <code>z</code> refers to a string buffer object 
 * whose current contents are "<code>start</code>", then 
 * the method call <code>z.append("le")</code> would cause the string 
 * buffer to contain "<code>startle</code>", whereas 
 * <code>z.insert(4, "le")</code> would alter the string buffer to 
 * contain "<code>starlet</code>". 
 * <p>
 * In general, if sb refers to an instance of a <code>StringBuffer</code>, 
 * then <code>sb.append(x)</code> has the same effect as 
 * <code>sb.insert(sb.length(),&nbsp;x)</code>.
 * <p>
 * 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. 
 *
 * @author	Arthur van Hoff
 * @version 	1.70, 12/03/01
 * @see     java.io.ByteArrayOutputStream
 * @see     java.lang.String
 * @since   JDK1.0
 */
 
public final class StringBuffer
    implements java.io.Serializable, CharSequence
{
    /**
     * The value is used for character storage.
     * 
     * @serial
     */
    private char value[];

    /** 
     * The count is the number of characters in the buffer.
     * 
     * @serial
     */
    private int count;

    /**
     * A flag indicating whether the buffer is shared 
     *
     * @serial
     */
    private boolean shared;

    /** use serialVersionUID from JDK 1.0.2 for interoperability */
    static final long serialVersionUID = 3388685877147921107L;

    /**
     * Constructs a string buffer with no characters in it and an 
     * initial capacity of 16 characters. 
     */
    public StringBuffer() {
	this(16);
    }

    /**
     * Constructs a string buffer with no characters in it and an 
     * initial capacity specified by the <code>length</code> argument. 
     *
     * @param      length   the initial capacity.
     * @exception  NegativeArraySizeException  if the <code>length</code>
     *               argument is less than <code>0</code>.
     */
    public StringBuffer(int length) {
	value = new char[length];
	shared = false;
    }

    /**
     * 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 
     * <code>16</code> plus the length of the string argument. 
     *
     * @param   str   the initial contents of the buffer.
     */
    public StringBuffer(String str) {
	this(str.length() + 16);
	append(str);
    }

    /**
     * Returns the length (character count) of this string buffer.
     *
     * @return  the length of the sequence of characters currently 
     *          represented by this string buffer.
     */
    public synchronized int length() {
	return count;
    }

    /**
     * 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.
     */
    public synchronized int capacity() {
	return value.length;
    }

    /**
     * Copies the buffer value.  This is normally only called when shared
     * is true.  It should only be called from a synchronized method.
     */
    private final void copy() {
	char newValue[] = new char[value.length];
	System.arraycopy(value, 0, newValue, 0, count);
	value = newValue;
	shared = false;
    }

    /**
     * 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: 
     * <ul>
     * <li>The <code>minimumCapacity</code> argument. 
     * <li>Twice the old capacity, plus <code>2</code>. 
     * </ul>
     * If the <code>minimumCapacity</code> argument is nonpositive, this
     * method takes no action and simply returns.
     *
     * @param   minimumCapacity   the minimum desired capacity.
     */
    public synchronized void ensureCapacity(int minimumCapacity) {
	if (minimumCapacity > value.length) {
	    expandCapacity(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)
     */
    private void expandCapacity(int minimumCapacity) {
	int newCapacity = (value.length + 1) * 2;
        if (newCapacity < 0) {
            newCapacity = Integer.MAX_VALUE;
        } else if (minimumCapacity > newCapacity) {
	    newCapacity = minimumCapacity;
	}
	
	char newValue[] = new char[newCapacity];
	System.arraycopy(value, 0, newValue, 0, count);
	value = newValue;
	shared = false;
    }

    /**
     * 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 <i>k</i> less than <code>newLength</code>, the character at 
     * index <i>k</i> in the new character sequence is the same as the 
     * character at index <i>k</i> in the old sequence if <i>k</i> is less 
     * than the length of the old character sequence; otherwise, it is the 
     * null character <code>'\u0000'</code>. 
     *  
     * In other words, if the <code>newLength</code> 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 
     * <code>newLength</code> argument. 
     * <p>
     * If the <code>newLength</code> argument is greater than or equal 
     * to the current length, sufficient null characters 
     * (<code>'&#92;u0000'</code>) are appended to the string buffer so that 
     * length becomes the <code>newLength</code> argument. 
     * <p>
     * The <code>newLength</code> argument must be greater than or equal 
     * to <code>0</code>. 
     *
     * @param      newLength   the new length of the buffer.
     * @exception  IndexOutOfBoundsException  if the
     *               <code>newLength</code> argument is negative.
     * @see        java.lang.StringBuffer#length()
     */
    public synchronized void setLength(int newLength) {
	if (newLength < 0) {
	    throw new StringIndexOutOfBoundsException(newLength);
	}
	
	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;
                }
            }
        }
    }

    /**
     * The specified character of the sequence currently represented by 
     * the string buffer, as indicated by the <code>index</code> argument, 
     * is returned. The first character of a string buffer is at index 
     * <code>0</code>, the next at index <code>1</code>, and so on, for 
     * array indexing. 
     * <p>
     * The index argument must be greater than or equal to 
     * <code>0</code>, 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 <code>index</code> is 
     *             negative or greater than or equal to <code>length()</code>.
     * @see        java.lang.StringBuffer#length()
     */
    public synchronized char charAt(int index) {
	if ((index < 0) || (index >= count)) {
	    throw new StringIndexOutOfBoundsException(index);
	}
	return value[index];
    }

    /**
     * Characters are copied from this string buffer into the 
     * destination character array <code>dst</code>. The first character to 
     * be copied is at index <code>srcBegin</code>; the last character to 
     * be copied is at index <code>srcEnd-1</code>. The total number of 
     * characters to be copied is <code>srcEnd-srcBegin</code>. The 
     * characters are copied into the subarray of <code>dst</code> starting 
     * at index <code>dstBegin</code> and ending at index:
     * <p><blockquote><pre>
     * dstbegin + (srcEnd-srcBegin) - 1
     * </pre></blockquote>
     *
     * @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 <code>dst</code>.
     * @exception  NullPointerException if <code>dst</code> is 
     *             <code>null</code>.
     * @exception  IndexOutOfBoundsException  if any of the following is true:
     *             <ul>
     *             <li><code>srcBegin</code> is negative
     *             <li><code>dstBegin</code> is negative
     *             <li>the <code>srcBegin</code> argument is greater than 
     *             the <code>srcEnd</code> argument.
     *             <li><code>srcEnd</code> is greater than 
     *             <code>this.length()</code>, the current length of this 
     *             string buffer.
     *             <li><code>dstBegin+srcEnd-srcBegin</code> is greater than 
     *             <code>dst.length</code>
     *             </ul>
     */
    public synchronized void getChars(int srcBegin, int srcEnd, char dst[], int dstBegin) {
	if (srcBegin < 0) {
	    throw new StringIndexOutOfBoundsException(srcBegin);
	}
	if ((srcEnd < 0) || (srcEnd > count)) {
	    throw new StringIndexOutOfBoundsException(srcEnd);
	}
        if (srcBegin > srcEnd) {
            throw new StringIndexOutOfBoundsException("srcBegin > srcEnd");
        }
	System.arraycopy(value, srcBegin, dst, dstBegin, srcEnd - srcBegin);
    }

    /**
     * The character at the specified index of this string buffer is set 
     * to <code>ch</code>. 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 <code>ch</code> at position 
     * <code>index</code>. 
     * <p>
     * The offset argument must be greater than or equal to 
     * <code>0</code>, 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 <code>index</code> is 
     *             negative or greater than or equal to <code>length()</code>.
     * @see        java.lang.StringBuffer#length()
     */
    public synchronized void setCharAt(int index, char ch) {
	if ((index < 0) || (index >= count)) {
	    throw new StringIndexOutOfBoundsException(index);
	}
	if (shared) copy();
	value[index] = ch;
    }

    /**
     * Appends the string representation of the <code>Object</code> 
     * argument to this string buffer. 
     * <p>
     * The argument is converted to a string as if by the method 
     * <code>String.valueOf</code>, and the characters of that 
     * string are then appended to this string buffer. 
     *
     * @param   obj   an <code>Object</code>.
     * @return  a reference to this <code>StringBuffer</code> object.
     * @see     java.lang.String#valueOf(java.lang.Object)
     * @see     java.lang.StringBuffer#append(java.lang.String)
     */
    public synchronized StringBuffer append(Object obj) {
	return append(String.valueOf(obj));
    }

    /**
     * Appends the string to this string buffer. 
     * <p>
     * The characters of the <code>String</code> 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 <code>str</code> is <code>null</code>, then the four characters 
     * <code>"null"</code> are appended to this string buffer.
     * <p>
     * Let <i>n</i> be the length of the old character sequence, the one 
     * contained in the string buffer just prior to execution of the 
     * <code>append</code> method. Then the character at index <i>k</i> in 
     * the new character sequence is equal to the character at index <i>k</i> 
     * in the old character sequence, if <i>k</i> is less than <i>n</i>; 
     * otherwise, it is equal to the character at index <i>k-n</i> in the 
     * argument <code>str</code>.
     *
     * @param   str   a string.
     * @return  a reference to this <code>StringBuffer</code>.
     */
    public synchronized StringBuffer append(String str) {
	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;
    }

    /**
     * Appends the specified <tt>StringBuffer</tt> to this
     * <tt>StringBuffer</tt>.
     * <p>
     * The characters of the <tt>StringBuffer</tt> argument are appended, 
     * in order, to the contents of this <tt>StringBuffer</tt>, increasing the 
     * length of this <tt>StringBuffer</tt> by the length of the argument. 
     * If <tt>sb</tt> is <tt>null</tt>, then the four characters 
     * <tt>"null"</tt> are appended to this <tt>StringBuffer</tt>.
     * <p>
     * Let <i>n</i> be the length of the old character sequence, the one 
     * contained in the <tt>StringBuffer</tt> just prior to execution of the 
     * <tt>append</tt> method. Then the character at index <i>k</i> in 
     * the new character sequence is equal to the character at index <i>k</i> 
     * in the old character sequence, if <i>k</i> is less than <i>n</i>; 
     * otherwise, it is equal to the character at index <i>k-n</i> in the 
     * argument <code>sb</code>.
     * <p>
     * The method <tt>ensureCapacity</tt> is first called on this
     * <tt>StringBuffer</tt> with the new buffer length as its argument.
     * (This ensures that the storage of this <tt>StringBuffer</tt> is
     * adequate to contain the additional characters being appended.)
     *
     * @param   sb         the <tt>StringBuffer</tt> to append.
     * @return  a reference to this <tt>StringBuffer</tt>.
     * @since 1.4
     */
    public synchronized StringBuffer append(StringBuffer sb) {
	if (sb == null) {
	    sb = NULL;
	}

	int len = sb.length();
	int newcount = count + len;
	if (newcount > value.length)
	    expandCapacity(newcount);
	sb.getChars(0, len, value, count);
	count = newcount;
	return this;
    }

    private static final StringBuffer NULL =  new StringBuffer("null");

    /**
     * Appends the string representation of the <code>char</code> array 
     * argument to this string buffer. 
     * <p>
     * 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. 
     * <p>
     * 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 <code>StringBuffer</code> object.
     *
     * @param   str   the characters to be appended.
     * @return  a reference to this <code>StringBuffer</code> object.
     */
    public synchronized StringBuffer append(char str[]) {
	int len = str.length;
	int newcount = count + len;
	if (newcount > value.length)
	    expandCapacity(newcount);
	System.arraycopy(str, 0, value, count, len);
	count = newcount;
	return this;
    }

    /**
     * Appends the string representation of a subarray of the 
     * <code>char</code> array argument to this string buffer. 
     * <p>
     * Characters of the character array <code>str</code>, starting at 
     * index <code>offset</code>, are appended, in order, to the contents 
     * of this string buffer. The length of this string buffer increases 
     * by the value of <code>len</code>. 
     * <p>
     * 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 <code>StringBuffer</code> 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 <code>StringBuffer</code> object.
     */
    public synchronized StringBuffer append(char str[], int offset, int len) {
        int newcount = count + len;
	if (newcount > value.length)
	    expandCapacity(newcount);
	System.arraycopy(str, offset, value, count, len);
	count = newcount;
	return this;
    }

    /**
     * Appends the string representation of the <code>boolean</code> 
     * argument to the string buffer. 
     * <p>
     * The argument is converted to a string as if by the method 
     * <code>String.valueOf</code>, and the characters of that 
     * string are then appended to this string buffer. 
     *
     * @param   b   a <code>boolean</code>.
     * @return  a reference to this <code>StringBuffer</code>.
     * @see     java.lang.String#valueOf(boolean)
     * @see     java.lang.StringBuffer#append(java.lang.String)
     */
    public StringBuffer append(boolean b) {
	return append(String.valueOf(b));
    }

    /**
     * Appends the string representation of the <code>char</code> 
     * argument to this string buffer. 
     * <p>
     * The argument is appended to the contents of this string buffer. 
     * The length of this string buffer increases by <code>1</code>. 
     * <p>
     * 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 
     * <code>StringBuffer</code> object.
     *
     * @param   c   a <code>char</code>.
     * @return  a reference to this <code>StringBuffer</code> object.
     */
    public synchronized StringBuffer append(char c) {
        int newcount = count + 1;
	if (newcount > value.length)
	    expandCapacity(newcount);
	value[count++] = c;
	return this;
    }

    /**
     * Appends the string representation of the <code>int</code> 
     * argument to this string buffer. 
     * <p>
     * The argument is converted to a string as if by the method 
     * <code>String.valueOf</code>, and the characters of that 
     * string are then appended to this string buffer. 
     *
     * @param   i   an <code>int</code>.
     * @return  a reference to this <code>StringBuffer</code> object.
     * @see     java.lang.String#valueOf(int)
     * @see     java.lang.StringBuffer#append(java.lang.String)
     */
    public StringBuffer append(int i) {
	return append(String.valueOf(i));
    }

    /**
     * Appends the string representation of the <code>long</code> 
     * argument to this string buffer. 
     * <p>
     * The argument is converted to a string as if by the method 
     * <code>String.valueOf</code>, and the characters of that 
     * string are then appended to this string buffer. 
     *
     * @param   l   a <code>long</code>.
     * @return  a reference to this <code>StringBuffer</code> object.
     * @see     java.lang.String#valueOf(long)
     * @see     java.lang.StringBuffer#append(java.lang.String)
     */
    public StringBuffer append(long l) {
	return append(String.valueOf(l));
    }

    /**
     * Appends the string representation of the <code>float</code> 
     * argument to this string buffer. 
     * <p>
     * The argument is converted to a string as if by the method 
     * <code>String.valueOf</code>, and the characters of that 
     * string are then appended to this string buffer. 
     *
     * @param   f   a <code>float</code>.
     * @return  a reference to this <code>StringBuffer</code> object.
     * @see     java.lang.String#valueOf(float)
     * @see     java.lang.StringBuffer#append(java.lang.String)
     */
    public StringBuffer append(float f) {
	return append(String.valueOf(f));
    }

    /**
     * Appends the string representation of the <code>double</code> 
     * argument to this string buffer. 
     * <p>
     * The argument is converted to a string as if by the method 
     * <code>String.valueOf</code>, and the characters of that 
     * string are then appended to this string buffer. 
     *
     * @param   d   a <code>double</code>.
     * @return  a reference to this <code>StringBuffer</code> object.
     * @see     java.lang.String#valueOf(double)
     * @see     java.lang.StringBuffer#append(java.lang.String)
     */
    public StringBuffer append(double d) {
	return append(String.valueOf(d));
    }

    /**
     * Removes the characters in a substring of this <code>StringBuffer</code>.
     * The substring begins at the specified <code>start</code> and extends to
     * the character at index <code>end - 1</code> or to the end of the
     * <code>StringBuffer</code> if no such character exists. If
     * <code>start</code> is equal to <code>end</code>, no changes are made.
     *
     * @param      start  The beginning index, inclusive.
     * @param      end    The ending index, exclusive.
     * @return     This string buffer.
     * @exception  StringIndexOutOfBoundsException  if <code>start</code>
     *             is negative, greater than <code>length()</code>, or
     *		   greater than <code>end</code>.
     * @since      1.2
     */
    public synchronized StringBuffer delete(int start, int end) {
	if (start < 0)
	    throw new StringIndexOutOfBoundsException(start);
	if (end > count)
	    end = count;
	if (start > end)
	    throw new StringIndexOutOfBoundsException();

        int len = end - start;
        if (len > 0) {
            if (shared)
                copy();
            System.arraycopy(value, start+len, value, start, count-end);
            count -= len;
        }
        return this;
    }

    /**
     * Removes the character at the specified position in this
     * <code>StringBuffer</code> (shortening the <code>StringBuffer</code>
     * by one character).
     *
     * @param       index  Index of character to remove
     * @return      This string buffer.
     * @exception   StringIndexOutOfBoundsException  if the <code>index</code>
     *		    is negative or greater than or equal to
     *		    <code>length()</code>.
     * @since       1.2
     */
    public synchronized StringBuffer deleteCharAt(int index) {
        if ((index < 0) || (index >= count))
	    throw new StringIndexOutOfBoundsException();
	if (shared)
	    copy();
	System.arraycopy(value, index+1, value, index, count-index-1);
	count--;
        return this;
    }

    /**
     * Replaces the characters in a substring of this <code>StringBuffer</code>
     * with characters in the specified <code>String</code>. The substring
     * begins at the specified <code>start</code> and extends to the character
     * at index <code>end - 1</code> or to the end of the
     * <code>StringBuffer</code> if no such character exists. First the
     * characters in the substring are removed and then the specified
     * <code>String</code> is inserted at <code>start</code>. (The
     * <code>StringBuffer</code> will be lengthened to accommodate the
     * specified String if necessary.)
     * 
     * @param      start    The beginning index, inclusive.
     * @param      end      The ending index, exclusive.
     * @param      str   String that will replace previous contents.
     * @return     This string buffer.
     * @exception  StringIndexOutOfBoundsException  if <code>start</code>
     *             is negative, greater than <code>length()</code>, or
     *		   greater than <code>end</code>.
     * @since      1.2
     */ 
    public synchronized StringBuffer replace(int start, int end, String str) {
        if (start < 0)
	    throw new StringIndexOutOfBoundsException(start);
	if (end > count)
	    end = count;
	if (start > end)
	    throw new StringIndexOutOfBoundsException();

	int len = str.length();
	int newCount = count + len - (end - start);
	if (newCount > value.length)
	    expandCapacity(newCount);
	else if (shared)
	    copy();

        System.arraycopy(value, end, value, start + len, count - end);
        str.getChars(0, len, value, start);
        count = newCount;
        return this;
    }

    /**
     * Returns a new <code>String</code> that contains a subsequence of
     * characters currently contained in this <code>StringBuffer</code>.The 
     * substring begins at the specified index and extends to the end of the
     * <code>StringBuffer</code>.
     * 
     * @param      start    The beginning index, inclusive.
     * @return     The new string.
     * @exception  StringIndexOutOfBoundsException  if <code>start</code> is
     *             less than zero, or greater than the length of this
     *             <code>StringBuffer</code>.
     * @since      1.2
     */
    public synchronized String substring(int start) {
        return substring(start, count);
    }

    /**
     * Returns a new character sequence that is a subsequence of this sequence.
     *
     * <p> An invocation of this method of the form
     *
     * <blockquote><pre>
     * sb.subSequence(begin,&nbsp;end)</pre></blockquote>
     *
     * behaves in exactly the same way as the invocation
     *
     * <blockquote><pre>
     * sb.substring(begin,&nbsp;end)</pre></blockquote>
     *
     * This method is provided so that the <tt>StringBuffer</tt> class can
     * implement the {@link CharSequence} interface. </p>
     *
     * @param      start   the start index, inclusive.
     * @param      end     the end index, exclusive.
     * @return     the specified subsequence.
     *
     * @throws  IndexOutOfBoundsException
     *          if <tt>start</tt> or <tt>end</tt> are negative,
     *          if <tt>end</tt> is greater than <tt>length()</tt>,
     *          or if <tt>start</tt> is greater than <tt>end</tt>
     *
     * @since 1.4
     * @spec JSR-51
     */
    public CharSequence subSequence(int start, int end) {
        return this.substring(start, end);
    }

    /**
     * Returns a new <code>String</code> that contains a subsequence of
     * characters currently contained in this <code>StringBuffer</code>. The 
     * substring begins at the specified <code>start</code> and 
     * extends to the character at index <code>end - 1</code>. An
     * exception is thrown if 
     *
     * @param      start    The beginning index, inclusive.
     * @param      end      The ending index, exclusive.
     * @return     The new string.
     * @exception  StringIndexOutOfBoundsException  if <code>start</code>
     *             or <code>end</code> are negative or greater than
     *		   <code>length()</code>, or <code>start</code> is
     *		   greater than <code>end</code>.
     * @since      1.2 
     */
    public synchronized String substring(int start, int end) {
	if (start < 0)
	    throw new StringIndexOutOfBoundsException(start);
	if (end > count)
	    throw new StringIndexOutOfBoundsException(end);
	if (start > end)
	    throw new StringIndexOutOfBoundsException(end - start);
        return new String(value, start, end - start);
    }

    /**
     * Inserts the string representation of a subarray of the <code>str</code>
     * array argument into this string buffer. The subarray begins at the
     * specified <code>offset</code> and extends <code>len</code> characters.
     * The characters of the subarray are inserted into this string buffer at
     * the position indicated by <code>index</code>. The length of this
     * <code>StringBuffer</code> increases by <code>len</code> characters.
     *
     * @param      index    position at which to insert subarray.
     * @param      str       A character array.
     * @param      offset   the index of the first character in subarray to
     *		   to be inserted.
     * @param      len      the number of characters in the subarray to
     *		   to be inserted.
     * @return     This string buffer.
     * @exception  StringIndexOutOfBoundsException  if <code>index</code>
     *             is negative or greater than <code>length()</code>, or
     *		   <code>offset</code> or <code>len</code> are negative, or
     *		   <code>(offset+len)</code> is greater than
     *		   <code>str.length</code>.
     * @since 1.2
     */
    public synchronized StringBuffer insert(int index, char str[], int offset,
                                                                   int len) {
        if ((index < 0) || (index > count))
	    throw new StringIndexOutOfBoundsException();
	if ((offset < 0) || (offset + len < 0) || (offset + len > str.length))
	    throw new StringIndexOutOfBoundsException(offset);
	if (len < 0)
	    throw new StringIndexOutOfBoundsException(len);
	int newCount = count + len;
	if (newCount > value.length)
	    expandCapacity(newCount);
	else if (shared)
	    copy();
	System.arraycopy(value, index, value, index + len, count - index);
	System.arraycopy(str, offset, value, index, len);
	count = newCount;
	return this;
    }

    /**
     * Inserts the string representation of the <code>Object</code> 
     * argument into this string buffer. 
     * <p>
     * The second argument is converted to a string as if by the method 
     * <code>String.valueOf</code>, and the characters of that 
     * string are then inserted into this string buffer at the indicated 
     * offset. 
     * <p>
     * The offset argument must be greater than or equal to 
     * <code>0</code>, and less than or equal to the length of this 
     * string buffer. 
     *
     * @param      offset   the offset.
     * @param      obj      an <code>Object</code>.
     * @return     a reference to this <code>StringBuffer</code> 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()
     */
    public synchronized StringBuffer insert(int offset, Object obj) {
	return insert(offset, String.valueOf(obj));
    }

    /**
     * Inserts the string into this string buffer. 
     * <p>
     * The characters of the <code>String</code> 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 
     * <code>str</code> is <code>null</code>, then the four characters 
     * <code>"null"</code> are inserted into this string buffer.
     * <p>
     * The character at index <i>k</i> in the new character sequence is 
     * equal to:
     * <ul>
     * <li>the character at index <i>k</i> in the old character sequence, if 
     * <i>k</i> is less than <code>offset</code> 
     * <li>the character at index <i>k</i><code>-offset</code> in the 
     * argument <code>str</code>, if <i>k</i> is not less than 
     * <code>offset</code> but is less than <code>offset+str.length()</code> 
     * <li>the character at index <i>k</i><code>-str.length()</code> in the 
     * old character sequence, if <i>k</i> is not less than 
     * <code>offset+str.length()</code>
     * </ul><p>
     * The offset argument must be greater than or equal to 
     * <code>0</code>, 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 <code>StringBuffer</code> object.
     * @exception  StringIndexOutOfBoundsException  if the offset is invalid.
     * @see        java.lang.StringBuffer#length()
     */
    public synchronized StringBuffer insert(int offset, String str) {
	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();
	System.arraycopy(value, offset, value, offset + len, count - offset);
	str.getChars(0, len, value, offset);
	count = newcount;
	return this;
    }

    /**
     * Inserts the string representation of the <code>char</code> array 
     * argument into this string buffer. 
     * <p>
     * The characters of the array argument are inserted into the 
     * contents of this string buffer at the position indicated by 
     * <code>offset</code>. The length of this string buffer increases by 
     * the length of the argument. 
     * <p>
     * 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 
     * <code>StringBuffer</code>  object at the position indicated by
     * <code>offset</code>.
     *
     * @param      offset   the offset.
     * @param      str      a character array.
     * @return     a reference to this <code>StringBuffer</code> object.
     * @exception  StringIndexOutOfBoundsException  if the offset is invalid.
     */
    public synchronized StringBuffer insert(int offset, char str[]) {
	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();
	System.arraycopy(value, offset, value, offset + len, count - offset);
	System.arraycopy(str, 0, value, offset, len);
	count = newcount;
	return this;
    }

    /**
     * Inserts the string representation of the <code>boolean</code> 
     * argument into this string buffer. 
     * <p>
     * The second argument is converted to a string as if by the method 
     * <code>String.valueOf</code>, and the characters of that 
     * string are then inserted into this string buffer at the indicated 
     * offset. 
     * <p>
     * The offset argument must be greater than or equal to 
     * <code>0</code>, and less than or equal to the length of this 
     * string buffer. 
     *
     * @param      offset   the offset.
     * @param      b        a <code>boolean</code>.
     * @return     a reference to this <code>StringBuffer</code> 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()
     */
    public StringBuffer insert(int offset, boolean b) {
	return insert(offset, String.valueOf(b));
    }

    /**
     * Inserts the string representation of the <code>char</code> 
     * argument into this string buffer. 
     * <p>
     * The second argument is inserted into the contents of this string 
     * buffer at the position indicated by <code>offset</code>. The length 
     * of this string buffer increases by one. 
     * <p>
     * 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 <code>StringBuffer</code> object at the position indicated by
     * <code>offset</code>.
     * <p>
     * The offset argument must be greater than or equal to 
     * <code>0</code>, and less than or equal to the length of this 
     * string buffer. 
     *
     * @param      offset   the offset.
     * @param      c        a <code>char</code>.
     * @return     a reference to this <code>StringBuffer</code> object.
     * @exception  IndexOutOfBoundsException  if the offset is invalid.
     * @see        java.lang.StringBuffer#length()
     */
    public synchronized StringBuffer insert(int offset, char c) {
	int newcount = count + 1;
	if (newcount > value.length)
	    expandCapacity(newcount);
	else if (shared)
	    copy();
	System.arraycopy(value, offset, value, offset + 1, count - offset);
	value[offset] = c;
	count = newcount;
	return this;
    }

    /**
     * Inserts the string representation of the second <code>int</code> 
     * argument into this string buffer. 
     * <p>
     * The second argument is converted to a string as if by the method 
     * <code>String.valueOf</code>, and the characters of that 
     * string are then inserted into this string buffer at the indicated 
     * offset. 
     * <p>
     * The offset argument must be greater than or equal to 
     * <code>0</code>, and less than or equal to the length of this 
     * string buffer. 
     *
     * @param      offset   the offset.
     * @param      i        an <code>int</code>.
     * @return     a reference to this <code>StringBuffer</code> 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()
     */
    public StringBuffer insert(int offset, int i) {
	return insert(offset, String.valueOf(i));
    }

    /**
     * Inserts the string representation of the <code>long</code> 
     * argument into this string buffer. 
     * <p>
     * The second argument is converted to a string as if by the method 
     * <code>String.valueOf</code>, and the characters of that 
     * string are then inserted into this string buffer at the position 
     * indicated by <code>offset</code>. 
     * <p>
     * The offset argument must be greater than or equal to 
     * <code>0</code>, and less than or equal to the length of this 
     * string buffer. 
     *
     * @param      offset   the offset.
     * @param      l        a <code>long</code>.
     * @return     a reference to this <code>StringBuffer</code> 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()
     */
    public StringBuffer insert(int offset, long l) {
	return insert(offset, String.valueOf(l));
    }

    /**
     * Inserts the string representation of the <code>float</code> 
     * argument into this string buffer. 
     * <p>
     * The second argument is converted to a string as if by the method 
     * <code>String.valueOf</code>, and the characters of that 
     * string are then inserted into this string buffer at the indicated 
     * offset. 
     * <p>
     * The offset argument must be greater than or equal to 
     * <code>0</code>, and less than or equal to the length of this 
     * string buffer. 
     *
     * @param      offset   the offset.
     * @param      f        a <code>float</code>.
     * @return     a reference to this <code>StringBuffer</code> 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()
     */
    public StringBuffer insert(int offset, float f) {
	return insert(offset, String.valueOf(f));
    }

    /**
     * Inserts the string representation of the <code>double</code> 
     * argument into this string buffer. 
     * <p>
     * The second argument is converted to a string as if by the method 
     * <code>String.valueOf</code>, and the characters of that 
     * string are then inserted into this string buffer at the indicated 
     * offset. 
     * <p>
     * The offset argument must be greater than or equal to 
     * <code>0</code>, and less than or equal to the length of this 
     * string buffer. 
     *
     * @param      offset   the offset.
     * @param      d        a <code>double</code>.
     * @return     a reference to this <code>StringBuffer</code> 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()
     */
    public StringBuffer insert(int offset, double d) {
	return insert(offset, String.valueOf(d));
    }

    /**
     * Returns the index within this string of the first occurrence of the
     * specified substring. The integer returned is the smallest value 
     * <i>k</i> such that:
     * <blockquote><pre>
     * this.toString().startsWith(str, <i>k</i>)
     * </pre></blockquote>
     * is <code>true</code>.
     *
     * @param   str   any string.
     * @return  if the string argument occurs as a substring within this
     *          object, then the index of the first character of the first
     *          such substring is returned; if it does not occur as a
     *          substring, <code>-1</code> is returned.
     * @exception java.lang.NullPointerException if <code>str</code> is 
     *          <code>null</code>.
     * @since   1.4
     */
    public int indexOf(String str) {
	return indexOf(str, 0);
    }

    /**
     * Returns the index within this string of the first occurrence of the
     * specified substring, starting at the specified index.  The integer
     * returned is the smallest value <tt>k</tt> for which:
     * <blockquote><pre>
     *     k >= Math.min(fromIndex, str.length()) &&
     *                   this.toString().startsWith(str, k)
     * </pre></blockquote>
     * If no such value of <i>k</i> exists, then -1 is returned.
     *
     * @param   str         the substring for which to search.
     * @param   fromIndex   the index from which to start the search.
     * @return  the index within this string of the first occurrence of the
     *          specified substring, starting at the specified index.
     * @exception java.lang.NullPointerException if <code>str</code> is
     *            <code>null</code>.
     * @since   1.4
     */
    public synchronized int indexOf(String str, int fromIndex) {
        return String.indexOf(value, 0, count,
                              str.toCharArray(), 0, str.length(), fromIndex);
    }

    /**
     * Returns the index within this string of the rightmost occurrence
     * of the specified substring.  The rightmost empty string "" is
     * considered to occur at the index value <code>this.length()</code>. 
     * The returned index is the largest value <i>k</i> such that 
     * <blockquote><pre>
     * this.toString().startsWith(str, k)
     * </pre></blockquote>
     * is true.
     *
     * @param   str   the substring to search for.
     * @return  if the string argument occurs one or more times as a substring
     *          within this object, then the index of the first character of
     *          the last such substring is returned. If it does not occur as
     *          a substring, <code>-1</code> is returned.
     * @exception java.lang.NullPointerException  if <code>str</code> is 
     *          <code>null</code>.
     * @since   1.4
     */
    public synchronized int lastIndexOf(String str) {
        return lastIndexOf(str, count);
    }

    /**
     * Returns the index within this string of the last occurrence of the
     * specified substring. The integer returned is the largest value <i>k</i>
     * such that:
     * <blockquote><pre>
     *     k <= Math.min(fromIndex, str.length()) &&
     *                   this.toString().startsWith(str, k)
     * </pre></blockquote>
     * If no such value of <i>k</i> exists, then -1 is returned.
     * 
     * @param   str         the substring to search for.
     * @param   fromIndex   the index to start the search from.
     * @return  the index within this string of the last occurrence of the
     *          specified substring.
     * @exception java.lang.NullPointerException if <code>str</code> is 
     *          <code>null</code>.
     * @since   1.4
     */
    public synchronized int lastIndexOf(String str, int fromIndex) {
        return String.lastIndexOf(value, 0, count,
                              str.toCharArray(), 0, str.length(), fromIndex);
    }

    /**
     * The character sequence contained in this string buffer is 
     * replaced by the reverse of the sequence. 
     * <p>
     * Let <i>n</i> be the length of the old character sequence, the one 
     * contained in the string buffer just prior to execution of the 
     * <code>reverse</code> method. Then the character at index <i>k</i> in 
     * the new character sequence is equal to the character at index 
     * <i>n-k-1</i> in the old character sequence.
     *
     * @return  a reference to this <code>StringBuffer</code> object.
     * @since   JDK1.0.2
     */
    public synchronized StringBuffer reverse() {
	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;
    }

    /**
     * Converts to a string representing the data in this string buffer.
     * A new <code>String</code> object is allocated and initialized to 
     * contain the character sequence currently represented by this 
     * string buffer. This <code>String</code> is then returned. Subsequent 
     * changes to the string buffer do not affect the contents of the 
     * <code>String</code>. 
     * <p>
     * Implementation advice: This method can be coded so as to create a new
     * <code>String</code> 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.
     */
    public String toString() {
	return new String(this);
    }

    //
    // The following two methods are needed by String to efficiently
    // convert a StringBuffer into a String.  They are not public.
    // They shouldn't be called by anyone but String.
    final void setShared() { shared = true; } 
    final char[] getValue() { return value; }

    /**
     * readObject is called to restore the state of the StringBuffer from
     * a stream.
     */
    private synchronized void readObject(java.io.ObjectInputStream s)
         throws java.io.IOException, ClassNotFoundException {
	s.defaultReadObject();
	value = (char[]) value.clone();
	shared = false;
    }
}
