java源码StringBuffer

/*
 * @(#)StringBuffer.java	1.99 04/07/15
 *
 * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.lang;

import sun.misc.FloatingDecimal;

/**
 * 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(),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 	1.99, 07/15/04
 * @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) {
        new FloatingDecimal(f).appendTo(this);
	return this;
    }

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