java 源碼 StringBuffer

/* * Copyright (c) 1994, 2008, Oracle and/or its affiliates. All rights reserved. * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. * * * * * * * * * * * * * * * * * * * * */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(), 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 * @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;    }    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;    }    /**     * @throws IndexOutOfBoundsException {@inheritDoc}     */    public synchronized StringBuffer append(char[] str, int offset, int len) {        super.append(str, offset, len);        return this;    }    public synchronized StringBuffer append(boolean b) {        super.append(b);        return this;    }    public synchronized StringBuffer append(char c) {        super.append(c);        return this;    }    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;    }    public synchronized StringBuffer append(long lng) {        super.append(lng);        return this;    }    public synchronized StringBuffer append(float f) {        super.append(f);        return this;    }    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}     */    public synchronized StringBuffer insert(int offset, Object obj) {        super.insert(offset, String.valueOf(obj));        return this;    }    /**     * @throws StringIndexOutOfBoundsException {@inheritDoc}     */    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}     */    public StringBuffer insert(int offset, boolean b) {        return insert(offset, String.valueOf(b));    }    /**     * @throws IndexOutOfBoundsException {@inheritDoc}     */    public synchronized StringBuffer insert(int offset, char c) {        super.insert(offset, c);        return this;    }    /**     * @throws StringIndexOutOfBoundsException {@inheritDoc}     */    public StringBuffer insert(int offset, int i) {        return insert(offset, String.valueOf(i));    }    /**     * @throws StringIndexOutOfBoundsException {@inheritDoc}     */    public StringBuffer insert(int offset, long l) {        return insert(offset, String.valueOf(l));    }    /**     * @throws StringIndexOutOfBoundsException {@inheritDoc}     */    public StringBuffer insert(int offset, float f) {        return insert(offset, String.valueOf(f));    }    /**     * @throws StringIndexOutOfBoundsException {@inheritDoc}     */    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 = fields.get("count", 0);    }}