StringBuffer与StringBuilder的区别

声明：以下内容如有雷同，纯属参考。

StringBuffer 多线程安全，执行速度慢，字符串变量
StringBuilder单线程不安全，执行速度快，字符串变量

  StringBuffer和StringBuilder类都表示内容可以被修改的字符串，StringBuilder是线程不安全的，运行效率高，如果一个字符串变量是在方法里面定义，这种情况只可能有一个线程访问它，不存在不安全的因素了，则用StringBuilder。如果要在类里面定义成员变量，并且这个类的实例对象会在多线程环境下使用，那么最好用StringBuffer。


为什么一个线程安全，一个线程不安全呢？
直接从源码来看更直接，我选jdk1.6下的StringBuffer 和 StringBuilder下的源码，进行比较，可以发现StringBuffer中的方法全部都添加了synchronized关键字。而StringBuilder中并没有。这就很明显了。

为什么一个执行效率高，一个执行效率慢？
本质上也是由多线程的加锁机制导致的。


StringBuffer 多线程 方法上加锁

package java.lang;
/**
 * A thread-safe, 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>
 * 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>
 * Whenever an operation occurs involving a source sequence (such as
 * appending or inserting from a source sequence) this class synchronizes
 * only on the string buffer performing the operation, not on the source.
 * <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. 
 *
 * As of  release JDK 5, this class has been supplemented with an equivalent 
 * class designed for use by a single thread, {@link StringBuilder}.  The 
 * <tt>StringBuilder</tt> class should generally be used in preference to 
 * this one, as it supports all of the same operations but it is faster, as 
 * it performs no synchronization.
 *
 * @author	Arthur van Hoff
 * @version 	%I%, %G%
 * @see     java.lang.StringBuilder
 * @see     java.lang.String
 * @since   JDK1.0
 */
 public final class StringBuffer
    extends AbstractStringBuilder
    implements java.io.Serializable, CharSequence
{

    /** 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() {
	super(16);
    }

    /**
     * Constructs a string buffer with no characters in it and 
     * the specified initial capacity. 
     *
     * @param      capacity  the initial capacity.
     * @exception  NegativeArraySizeException  if the <code>capacity</code>
     *               argument is less than <code>0</code>.
     */
    public StringBuffer(int capacity) {
	super(capacity);
    }

    /**
     * Constructs a string buffer initialized to the contents of the 
     * specified 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.
     * @exception NullPointerException if <code>str</code> is <code>null</code>
     */
    public StringBuffer(String str) {
	super(str.length() + 16);
	append(str);
    }

    /**
     * Constructs a string buffer that contains the same characters
     * as the specified <code>CharSequence</code>. The initial capacity of
     * the string buffer is <code>16</code> plus the length of the
     * <code>CharSequence</code> argument.
     * <p>
     * If the length of the specified <code>CharSequence</code> is
     * less than or equal to zero, then an empty buffer of capacity
     * <code>16</code> is returned.
     *
     * @param      seq   the sequence to copy.
     * @exception NullPointerException if <code>seq</code> is <code>null</code>
     * @since 1.5
     */
    public StringBuffer(CharSequence seq) {
        this(seq.length() + 16);
        append(seq);
    }

    public synchronized int length() {
	return count;
    }

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


    public synchronized void ensureCapacity(int minimumCapacity) {
	if (minimumCapacity > value.length) {
	    expandCapacity(minimumCapacity);
	}
    }

    /**
     * @since      1.5
     */
    public synchronized void trimToSize() {
        super.trimToSize();
    }

    /**
     * @throws IndexOutOfBoundsException {@inheritDoc}
     * @see        #length()
     */
    public synchronized void setLength(int newLength) {
	super.setLength(newLength);
    }

    /**
     * @throws IndexOutOfBoundsException {@inheritDoc}
     * @see        #length()
     */
    public synchronized char charAt(int index) {
	if ((index < 0) || (index >= count))
	    throw new StringIndexOutOfBoundsException(index);
	return value[index];
    }

    /**
     * @since      1.5
     */
    public synchronized int codePointAt(int index) {
        return super.codePointAt(index);
    }

    /**
     * @since     1.5
     */
    public synchronized int codePointBefore(int index) {
        return super.codePointBefore(index);
    }

    /**
     * @since     1.5
     */
    public synchronized int codePointCount(int beginIndex, int endIndex) {
	return super.codePointCount(beginIndex, endIndex);
    }

    /**
     * @since     1.5
     */
    public synchronized int offsetByCodePoints(int index, int codePointOffset) {
	return super.offsetByCodePoints(index, codePointOffset);
    }

    /**
     * @throws NullPointerException {@inheritDoc}
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    public synchronized void getChars(int srcBegin, int srcEnd, char dst[],
                                      int dstBegin)
    {
	super.getChars(srcBegin, srcEnd, dst, dstBegin);
    }

    /**
     * @throws IndexOutOfBoundsException {@inheritDoc}
     * @see        #length()
     */
    public synchronized void setCharAt(int index, char ch) {
	if ((index < 0) || (index >= count))
	    throw new StringIndexOutOfBoundsException(index);
	value[index] = ch;
    }

    /**
     * @see     java.lang.String#valueOf(java.lang.Object)
     * @see     #append(java.lang.String)
     */
    public synchronized StringBuffer append(Object obj) {
	super.append(String.valueOf(obj));
        return this;
    }

    public synchronized StringBuffer append(String str) {
	super.append(str);
        return this;
    }

    /**
     * Appends the specified <tt>StringBuffer</tt> to this sequence.
     * <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>
     * This method synchronizes on <code>this</code> (the destination) 
     * object but does not synchronize on the source (<code>sb</code>).
     *
     * @param   sb   the <tt>StringBuffer</tt> to append.
     * @return  a reference to this object.
     * @since 1.4
     */
    public synchronized StringBuffer append(StringBuffer sb) {
        super.append(sb);
        return this;
    }


    /**
     * Appends the specified <code>CharSequence</code> to this
     * sequence.
     * <p>
     * The characters of the <code>CharSequence</code> argument are appended, 
     * in order, increasing the length of this sequence by the length of the 
     * argument.
     *
     * <p>The result of this method is exactly the same as if it were an
     * invocation of this.append(s, 0, s.length());
     *
     * <p>This method synchronizes on this (the destination) 
     * object but does not synchronize on the source (<code>s</code>).
     *
     * <p>If <code>s</code> is <code>null</code>, then the four characters 
     * <code>"null"</code> are appended.
     *
     * @param   s the <code>CharSequence</code> to append.
     * @return  a reference to this object.
     * @since 1.5
     */
    public StringBuffer append(CharSequence s) {
        // Note, synchronization achieved via other invocations
        if (s == null)
            s = "null";
        if (s instanceof String)
            return this.append((String)s);
        if (s instanceof StringBuffer)
            return this.append((StringBuffer)s);
        return this.append(s, 0, s.length());
    }

    /**
     * @throws IndexOutOfBoundsException {@inheritDoc}
     * @since      1.5
     */
    public synchronized StringBuffer append(CharSequence s, int start, int end) 
    {
        super.append(s, start, end);
        return this;
    }

    public synchronized StringBuffer append(char str[]) { 
        super.append(str);
        return this;
    }

    public synchronized StringBuffer append(char str[], int offset, int len) {
        super.append(str, offset, len);
        return this;
    }

    /**
     * @see     java.lang.String#valueOf(boolean)
     * @see     #append(java.lang.String)
     */
    public synchronized StringBuffer append(boolean b) {
        super.append(b);
        return this;
    }

    public synchronized StringBuffer append(char c) {
        super.append(c);
        return this;
    }

    /**
     * @see     java.lang.String#valueOf(int)
     * @see     #append(java.lang.String)
     */
    public synchronized StringBuffer append(int i) {
	super.append(i);
        return this;
    }

    /**
     * @since 1.5
     */
    public synchronized StringBuffer appendCodePoint(int codePoint) {
	super.appendCodePoint(codePoint);
	return this;
    }

    /**
     * @see     java.lang.String#valueOf(long)
     * @see     #append(java.lang.String)
     */
    public synchronized StringBuffer append(long lng) {
        super.append(lng);
	return this;
    }

    /**
     * @see     java.lang.String#valueOf(float)
     * @see     #append(java.lang.String)
     */
    public synchronized StringBuffer append(float f) {
	super.append(f);
	return this;
    }

    /**
     * @see     java.lang.String#valueOf(double)
     * @see     #append(java.lang.String)
     */
    public synchronized StringBuffer append(double d) {
	super.append(d);
	return this;
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @since      1.2
     */
    public synchronized StringBuffer delete(int start, int end) {
        super.delete(start, end);
        return this;
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @since      1.2
     */
    public synchronized StringBuffer deleteCharAt(int index) {
        super.deleteCharAt(index);
        return this;
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @since      1.2
     */
    public synchronized StringBuffer replace(int start, int end, String str) {
        super.replace(start, end, str);
        return this;
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @since      1.2
     */
    public synchronized String substring(int start) {
        return substring(start, count);
    }

    /**
     * @throws IndexOutOfBoundsException {@inheritDoc}
     * @since      1.4
     */
    public synchronized CharSequence subSequence(int start, int end) {
        return super.substring(start, end);
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @since      1.2
     */
    public synchronized String substring(int start, int end) {
        return super.substring(start, end);
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @since      1.2
     */
    public synchronized StringBuffer insert(int index, char str[], int offset,
                                            int len) 
    {
        super.insert(index, str, offset, len);
        return this;
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @see        java.lang.String#valueOf(java.lang.Object)
     * @see        #insert(int, java.lang.String)
     * @see        #length()
     */
    public synchronized StringBuffer insert(int offset, Object obj) {
	super.insert(offset, String.valueOf(obj));
        return this;
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @see        #length()
     */
    public synchronized StringBuffer insert(int offset, String str) {
        super.insert(offset, str);
        return this;
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     */
    public synchronized StringBuffer insert(int offset, char str[]) {
        super.insert(offset, str);
	return this;
    }

    /**
     * @throws IndexOutOfBoundsException {@inheritDoc}
     * @since      1.5
     */
    public StringBuffer insert(int dstOffset, CharSequence s) {
        // Note, synchronization achieved via other invocations
        if (s == null)
            s = "null";
        if (s instanceof String)
            return this.insert(dstOffset, (String)s);
        return this.insert(dstOffset, s, 0, s.length());
    }

    /**
     * @throws IndexOutOfBoundsException {@inheritDoc}
     * @since      1.5
     */
    public synchronized StringBuffer insert(int dstOffset, CharSequence s, 
                                            int start, int end)
    {
        super.insert(dstOffset, s, start, end);
        return this;
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @see        java.lang.String#valueOf(boolean)
     * @see        #insert(int, java.lang.String)
     * @see        #length()
     */
    public StringBuffer insert(int offset, boolean b) {
	return insert(offset, String.valueOf(b));
    }

    /**
     * @throws IndexOutOfBoundsException {@inheritDoc}
     * @see        #length()
     */
    public synchronized StringBuffer insert(int offset, char c) {
	super.insert(offset, c);
	return this;
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @see        java.lang.String#valueOf(int)
     * @see        #insert(int, java.lang.String)
     * @see        #length()
     */
    public StringBuffer insert(int offset, int i) {
	return insert(offset, String.valueOf(i));
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @see        java.lang.String#valueOf(long)
     * @see        #insert(int, java.lang.String)
     * @see        #length()
     */
    public StringBuffer insert(int offset, long l) {
	return insert(offset, String.valueOf(l));
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @see        java.lang.String#valueOf(float)
     * @see        #insert(int, java.lang.String)
     * @see        #length()
     */
    public StringBuffer insert(int offset, float f) {
	return insert(offset, String.valueOf(f));
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @see        java.lang.String#valueOf(double)
     * @see        #insert(int, java.lang.String)
     * @see        #length()
     */
    public StringBuffer insert(int offset, double d) {
	return insert(offset, String.valueOf(d));
    }

    /**
     * @throws NullPointerException {@inheritDoc}
     * @since      1.4
     */
    public int indexOf(String str) {
	return indexOf(str, 0);
    }

    /**
     * @throws NullPointerException {@inheritDoc}
     * @since      1.4
     */
    public synchronized int indexOf(String str, int fromIndex) {
        return String.indexOf(value, 0, count,
                              str.toCharArray(), 0, str.length(), fromIndex);
    }

    /**
     * @throws NullPointerException {@inheritDoc}
     * @since      1.4
     */
    public int lastIndexOf(String str) {
        // Note, synchronization achieved via other invocations
        return lastIndexOf(str, count);
    }

    /**
     * @throws NullPointerException {@inheritDoc}
     * @since      1.4
     */
    public synchronized int lastIndexOf(String str, int fromIndex) {
        return String.lastIndexOf(value, 0, count,
                              str.toCharArray(), 0, str.length(), fromIndex);
    }

    /**
     * @since   JDK1.0.2
     */
    public synchronized StringBuffer reverse() {
	super.reverse();
	return this;
    }

    public synchronized String toString() {
	return new String(value, 0, count);
    }

    /**
     * Serializable fields for StringBuffer.
     * 
     * @serialField value  char[]
     *              The backing character array of this StringBuffer.
     * @serialField count int
     *              The number of characters in this StringBuffer.
     * @serialField shared  boolean
     *              A flag indicating whether the backing array is shared. 
     *              The value is ignored upon deserialization.
     */
    private static final java.io.ObjectStreamField[] serialPersistentFields = 
    { 
        new java.io.ObjectStreamField("value", char[].class), 
        new java.io.ObjectStreamField("count", Integer.TYPE),
        new java.io.ObjectStreamField("shared", Boolean.TYPE),
    };

    /**
     * readObject is called to restore the state of the StringBuffer from
     * a stream.
     */
    private synchronized void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException {
        java.io.ObjectOutputStream.PutField fields = s.putFields();
        fields.put("value", value);
        fields.put("count", count);
        fields.put("shared", false);
        s.writeFields();
    }

    /**
     * readObject is called to restore the state of the StringBuffer from
     * a stream.
     */
    private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        java.io.ObjectInputStream.GetField fields = s.readFields();
        value = (char[])fields.get("value", null);
        count = (int)fields.get("count", 0);
    }
}

StringBuilder方法上则没有加锁就是单线程。

/*
 * %W% %E%
 *
 * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.lang;


/**
 * A mutable sequence of characters.  This class provides an API compatible
 * with <code>StringBuffer</code>, but with no guarantee of synchronization.
 * This class is designed for use as a drop-in replacement for
 * <code>StringBuffer</code> in places where the string buffer was being
 * used by a single thread (as is generally the case).   Where possible,
 * it is recommended that this class be used in preference to
 * <code>StringBuffer</code> as it will be faster under most implementations.
 * 
 * <p>The principal operations on a <code>StringBuilder</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 builder. The 
 * <code>append</code> method always adds these characters at the end 
 * of the builder; the <code>insert</code> method adds the characters at 
 * a specified point. 
 * <p>
 * For example, if <code>z</code> refers to a string builder object 
 * whose current contents are "<code>start</code>", then 
 * the method call <code>z.append("le")</code> would cause the string 
 * builder to contain "<code>startle</code>", whereas 
 * <code>z.insert(4, "le")</code> would alter the string builder to 
 * contain "<code>starlet</code>". 
 * <p>
 * In general, if sb refers to an instance of a <code>StringBuilder</code>, 
 * then <code>sb.append(x)</code> has the same effect as 
 * <code>sb.insert(sb.length(),&nbsp;x)</code>.
 *
 * Every string builder has a capacity. As long as the length of the 
 * character sequence contained in the string builder does not exceed 
 * the capacity, it is not necessary to allocate a new internal 
 * buffer. If the internal buffer overflows, it is automatically made larger.
 *
 * <p>Instances of <code>StringBuilder</code> are not safe for
 * use by multiple threads. If such synchronization is required then it is
 * recommended that {@link java.lang.StringBuffer} be used. 
 *
 * @author	Michael McCloskey
 * @version 	%I%, %G%
 * @see         java.lang.StringBuffer
 * @see         java.lang.String
 * @since	1.5
 */
public final class StringBuilder
    extends AbstractStringBuilder
    implements java.io.Serializable, CharSequence
{

    /** use serialVersionUID for interoperability */
    static final long serialVersionUID = 4383685877147921099L;

    /**
     * Constructs a string builder with no characters in it and an 
     * initial capacity of 16 characters. 
     */
    public StringBuilder() {
	super(16);
    }

    /**
     * Constructs a string builder with no characters in it and an 
     * initial capacity specified by the <code>capacity</code> argument. 
     *
     * @param      capacity  the initial capacity.
     * @throws     NegativeArraySizeException  if the <code>capacity</code>
     *               argument is less than <code>0</code>.
     */
    public StringBuilder(int capacity) {
	super(capacity);
    }

    /**
     * Constructs a string builder initialized to the contents of the 
     * specified string. The initial capacity of the string builder is 
     * <code>16</code> plus the length of the string argument.  
     *
     * @param   str   the initial contents of the buffer.
     * @throws    NullPointerException if <code>str</code> is <code>null</code>
     */
    public StringBuilder(String str) {
	super(str.length() + 16);
	append(str);
    }

    /**
     * Constructs a string builder that contains the same characters
     * as the specified <code>CharSequence</code>. The initial capacity of
     * the string builder is <code>16</code> plus the length of the
     * <code>CharSequence</code> argument.
     *
     * @param      seq   the sequence to copy.
     * @throws    NullPointerException if <code>seq</code> is <code>null</code>
     */
    public StringBuilder(CharSequence seq) {
        this(seq.length() + 16);
        append(seq);
    }

    /**
     * @see     java.lang.String#valueOf(java.lang.Object)
     * @see     #append(java.lang.String)
     */
    public StringBuilder append(Object obj) {
	return append(String.valueOf(obj));
    }

    public StringBuilder append(String str) {
	super.append(str);
        return this;
    }

    // Appends the specified string builder to this sequence.
    private StringBuilder append(StringBuilder sb) {
	if (sb == null)
            return append("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;
    }

    /**
     * Appends the specified <tt>StringBuffer</tt> to this sequence.
     * <p>
     * The characters of the <tt>StringBuffer</tt> argument are appended, 
     * in order, to this sequence, increasing the 
     * length of this sequence 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 sequence.
     * <p>
     * Let <i>n</i> be the length of this character sequence 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>.
     *
     * @param   sb   the <tt>StringBuffer</tt> to append.
     * @return  a reference to this object.
     */
    public StringBuilder append(StringBuffer sb) {
        super.append(sb);
        return this;
    }

    /**
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    public StringBuilder append(CharSequence s) {
        if (s == null)
            s = "null";
        if (s instanceof String)
            return this.append((String)s);
        if (s instanceof StringBuffer)
            return this.append((StringBuffer)s);
        if (s instanceof StringBuilder)
            return this.append((StringBuilder)s);
        return this.append(s, 0, s.length());
    }

    /**
     * @throws     IndexOutOfBoundsException {@inheritDoc}
     */
    public StringBuilder append(CharSequence s, int start, int end) {
        super.append(s, start, end);
        return this;
    }

    public StringBuilder append(char str[]) { 
	super.append(str);
        return this;
    }

    public StringBuilder append(char str[], int offset, int len) {
        super.append(str, offset, len);
        return this;
    }

    /**
     * @see     java.lang.String#valueOf(boolean)
     * @see     #append(java.lang.String)
     */
    public StringBuilder append(boolean b) {
        super.append(b);
        return this;
    }

    public StringBuilder append(char c) {
        super.append(c);
        return this;
    }

    /**
     * @see     java.lang.String#valueOf(int)
     * @see     #append(java.lang.String)
     */
    public StringBuilder append(int i) {
	super.append(i);
        return this;
    }

    /**
     * @see     java.lang.String#valueOf(long)
     * @see     #append(java.lang.String)
     */
    public StringBuilder append(long lng) {
        super.append(lng);
        return this;
    }

    /**
     * @see     java.lang.String#valueOf(float)
     * @see     #append(java.lang.String)
     */
    public StringBuilder append(float f) {
	super.append(f);
        return this;
    }

    /**
     * @see     java.lang.String#valueOf(double)
     * @see     #append(java.lang.String)
     */
    public StringBuilder append(double d) {
	super.append(d);
        return this;
    }

    /**
     * @since 1.5
     */
    public StringBuilder appendCodePoint(int codePoint) {
	super.appendCodePoint(codePoint);
	return this;
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     */
    public StringBuilder delete(int start, int end) {
	super.delete(start, end);
        return this;
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     */
    public StringBuilder deleteCharAt(int index) {
        super.deleteCharAt(index);
        return this;
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     */
    public StringBuilder replace(int start, int end, String str) {
        super.replace(start, end, str);
        return this;
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     */
    public StringBuilder insert(int index, char str[], int offset,
                                int len) 
    {
        super.insert(index, str, offset, len);
	return this;
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @see        java.lang.String#valueOf(java.lang.Object)
     * @see        #insert(int, java.lang.String)
     * @see        #length()
     */
    public StringBuilder insert(int offset, Object obj) {
	return insert(offset, String.valueOf(obj));
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @see        #length()
     */
    public StringBuilder insert(int offset, String str) {
	super.insert(offset, str);
        return this;
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     */
    public StringBuilder insert(int offset, char str[]) {
	super.insert(offset, str);
        return this;
    }

    /**
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    public StringBuilder insert(int dstOffset, CharSequence s) {
        if (s == null)
            s = "null";
        if (s instanceof String)
            return this.insert(dstOffset, (String)s);
        return this.insert(dstOffset, s, 0, s.length());
    }

    /**
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    public StringBuilder insert(int dstOffset, CharSequence s,
				int start, int end)
    {
        super.insert(dstOffset, s, start, end);
        return this;
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @see        java.lang.String#valueOf(boolean)
     * @see        #insert(int, java.lang.String)
     * @see        #length()
     */
    public StringBuilder insert(int offset, boolean b) {
	super.insert(offset, b);
        return this;
    }

    /**
     * @throws IndexOutOfBoundsException {@inheritDoc}
     * @see        #length()
     */
    public StringBuilder insert(int offset, char c) {
        super.insert(offset, c);
	return this;
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @see        java.lang.String#valueOf(int)
     * @see        #insert(int, java.lang.String)
     * @see        #length()
     */
    public StringBuilder insert(int offset, int i) {
	return insert(offset, String.valueOf(i));
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @see        java.lang.String#valueOf(long)
     * @see        #insert(int, java.lang.String)
     * @see        #length()
     */
    public StringBuilder insert(int offset, long l) {
	return insert(offset, String.valueOf(l));
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @see        java.lang.String#valueOf(float)
     * @see        #insert(int, java.lang.String)
     * @see        #length()
     */
    public StringBuilder insert(int offset, float f) {
	return insert(offset, String.valueOf(f));
    }

    /**
     * @throws StringIndexOutOfBoundsException {@inheritDoc}
     * @see        java.lang.String#valueOf(double)
     * @see        #insert(int, java.lang.String)
     * @see        #length()
     */
    public StringBuilder insert(int offset, double d) {
	return insert(offset, String.valueOf(d));
    }

    /**
     * @throws NullPointerException {@inheritDoc}
     */
    public int indexOf(String str) {
	return indexOf(str, 0);
    }

    /**
     * @throws NullPointerException {@inheritDoc}
     */
    public int indexOf(String str, int fromIndex) {
        return String.indexOf(value, 0, count,
                              str.toCharArray(), 0, str.length(), fromIndex);
    }

    /**
     * @throws NullPointerException {@inheritDoc}
     */
    public int lastIndexOf(String str) {
        return lastIndexOf(str, count);
    }

    /**
     * @throws NullPointerException {@inheritDoc}
     */
    public int lastIndexOf(String str, int fromIndex) {
        return String.lastIndexOf(value, 0, count,
                              str.toCharArray(), 0, str.length(), fromIndex);
    }

    public StringBuilder reverse() {
	super.reverse();
	return this;
    }

    public String toString() {
        // Create a copy, don't share the array
	return new String(value, 0, count);
    }

    /**
     * Save the state of the <tt>StringBuilder</tt> instance to a stream 
     * (that is, serialize it).
     *
     * @serialData the number of characters currently stored in the string
     *             builder (<tt>int</tt>), followed by the characters in the
     *             string builder (<tt>char[]</tt>).   The length of the
     *             <tt>char</tt> array may be greater than the number of 
     *             characters currently stored in the string builder, in which
     *             case extra characters are ignored.
     */
    private void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException {
        s.defaultWriteObject();
        s.writeInt(count);
        s.writeObject(value);
    }

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

}