/*

 * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.lang;

import java.util.Arrays;

/**

 * 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} are the

 * {@code append} and {@code insert} methods, which are

 * overloaded so as to accept data of any type. Each effectively

 * converts a given datum to a string and then appends or inserts the

 * characters of that string to the string buffer. The

 * {@code append} method always adds these characters at the end

 * of the buffer; the {@code insert} method adds the characters at

 * a specified point.

 * <p>

 * For example, if {@code z} refers to a string buffer object

 * whose current contents are {@code "start"}, then

 * the method call {@code z.append("le")} would cause the string

 * buffer to contain {@code "startle"}, whereas

 * {@code z.insert(4, "le")} would alter the string buffer to

 * contain {@code "starlet"}.

 * <p>

 * In general, if sb refers to an instance of a {@code StringBuffer},

 * then {@code sb.append(x)} has the same effect as

 * {@code sb.insert(sb.length(), x)}.

 * <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.

 * Note that while {@code StringBuffer} is designed to be safe to use

 * concurrently from multiple threads, if the constructor or the

 * {@code append} or {@code insert} operation is passed a source sequence

 * that is shared across threads, the calling code must ensure

 * that the operation has a consistent and unchanging view of the source

 * sequence for the duration of the operation.

 * This could be satisfied by the caller holding a lock during the

 * operation's call, by using an immutable source sequence, or by not

 * sharing the source sequence across threads.

 * <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.

 * <p>

 * Unless otherwise noted, passing a {@code null} argument to a constructor

 * or method in this class will cause a {@link NullPointerException} to be

 * thrown.

 * <p>

 * As of  release JDK 5, this class has been supplemented with an equivalent

 * class designed for use by a single thread, {@link StringBuilder}.  The

 * {@code StringBuilder} 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   1.0

 */

 public final class StringBuffer

    extends AbstractStringBuilder

    implements java.io.Serializable, CharSequence

{

    /**

     * A cache of the last value returned by toString. Cleared

     * whenever the StringBuffer is modified.

     */

    private transient char[] toStringCache;

    /** 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}

     *               argument is less than {@code 0}.

     */

    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} plus the length of the string argument.

     *

     * @param   str   the initial contents of the buffer.

     */

    public StringBuffer(String str) {

        super(str.length() + 16);

        append(str);

    }

    /**

     * Constructs a string buffer that contains the same characters

     * as the specified {@code CharSequence}. The initial capacity of

     * the string buffer is {@code 16} plus the length of the

     * {@code CharSequence} argument.

     * <p>

     * If the length of the specified {@code CharSequence} is

     * less than or equal to zero, then an empty buffer of capacity

     * {@code 16} is returned.

     *

     * @param      seq   the sequence to copy.

     * @since 1.5

     */

    public StringBuffer(CharSequence seq) {

        this(seq.length() + 16);

        append(seq);

    }

    @Override

    public synchronized int length() {

        return count;

    }

    @Override

    public synchronized int capacity() {

        return value.length;

    }

    @Override

    public synchronized void ensureCapacity(int minimumCapacity) {

        if (minimumCapacity > value.length) {

            expandCapacity(minimumCapacity);

        }

    }

    /**

     * @since      1.5

     */

    @Override

    public synchronized void trimToSize() {

        super.trimToSize();

    }

    /**

     * @throws IndexOutOfBoundsException {@inheritDoc}

     * @see        #length()

     */

    @Override

    public synchronized void setLength(int newLength) {

        toStringCache = null;

        super.setLength(newLength);

    }

    /**

     * @throws IndexOutOfBoundsException {@inheritDoc}

     * @see        #length()

     */

    @Override

    public synchronized char charAt(int index) {

        if ((index < 0) || (index >= count))

            throw new StringIndexOutOfBoundsException(index);

        return value[index];

    }

    /**

     * @since      1.5

     */

    @Override

    public synchronized int codePointAt(int index) {

        return super.codePointAt(index);

    }

    /**

     * @since     1.5

     */

    @Override

    public synchronized int codePointBefore(int index) {

        return super.codePointBefore(index);

    }

    /**

     * @since     1.5

     */

    @Override

    public synchronized int codePointCount(int beginIndex, int endIndex) {

        return super.codePointCount(beginIndex, endIndex);

    }

    /**

     * @since     1.5

     */

    @Override

    public synchronized int offsetByCodePoints(int index, int codePointOffset) {

        return super.offsetByCodePoints(index, codePointOffset);

    }

    /**

     * @throws IndexOutOfBoundsException {@inheritDoc}

     */

    @Override

    public synchronized void getChars(int srcBegin, int srcEnd, char[] dst,

                                      int dstBegin)

    {

        super.getChars(srcBegin, srcEnd, dst, dstBegin);

    }

    /**

     * @throws IndexOutOfBoundsException {@inheritDoc}

     * @see        #length()

     */

    @Override

    public synchronized void setCharAt(int index, char ch) {

        if ((index < 0) || (index >= count))

            throw new StringIndexOutOfBoundsException(index);

        toStringCache = null;

        value[index] = ch;

    }

    @Override

    public synchronized StringBuffer append(Object obj) {

        toStringCache = null;

        super.append(String.valueOf(obj));

        return this;

    }

    @Override

    public synchronized StringBuffer append(String str) {

        toStringCache = null;

        super.append(str);

        return this;

    }

    /**

     * Appends the specified {@code StringBuffer} to this sequence.

     * <p>

     * The characters of the {@code StringBuffer} argument are appended,

     * in order, to the contents of this {@code StringBuffer}, increasing the

     * length of this {@code StringBuffer} by the length of the argument.

     * If {@code sb} is {@code null}, then the four characters

     * {@code "null"} are appended to this {@code StringBuffer}.

     * <p>

     * Let <i>n</i> be the length of the old character sequence, the one

     * contained in the {@code StringBuffer} just prior to execution of the

     * {@code append} 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}.

     * <p>

     * This method synchronizes on {@code this}, the destination

     * object, but does not synchronize on the source ({@code sb}).

     *

     * @param   sb   the {@code StringBuffer} to append.

     * @return  a reference to this object.

     * @since 1.4

     */

    public synchronized StringBuffer append(StringBuffer sb) {

        toStringCache = null;

        super.append(sb);

        return this;

    }

    /**

     * @since 1.8

     */

    @Override

    synchronized StringBuffer append(AbstractStringBuilder asb) {

        toStringCache = null;

        super.append(asb);

        return this;

    }

    /**

     * Appends the specified {@code CharSequence} to this

     * sequence.

     * <p>

     * The characters of the {@code CharSequence} 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 {@code this}, the destination

     * object, but does not synchronize on the source ({@code s}).

     *

     * <p>If {@code s} is {@code null}, then the four characters

     * {@code "null"} are appended.

     *

     * @param   s the {@code CharSequence} to append.

     * @return  a reference to this object.

     * @since 1.5

     */

    @Override

    public synchronized StringBuffer append(CharSequence s) {

        toStringCache = null;

        super.append(s);

        return this;

    }

    /**

     * @throws IndexOutOfBoundsException {@inheritDoc}

     * @since      1.5

     */

    @Override

    public synchronized StringBuffer append(CharSequence s, int start, int end)

    {

        toStringCache = null;

        super.append(s, start, end);

        return this;

    }

    @Override

    public synchronized StringBuffer append(char[] str) {

        toStringCache = null;

        super.append(str);

        return this;

    }

    /**

     * @throws IndexOutOfBoundsException {@inheritDoc}

     */

    @Override

    public synchronized StringBuffer append(char[] str, int offset, int len) {

        toStringCache = null;

        super.append(str, offset, len);

        return this;

    }

    @Override

    public synchronized StringBuffer append(boolean b) {

        toStringCache = null;

        super.append(b);

        return this;

    }

    @Override

    public synchronized StringBuffer append(char c) {

        toStringCache = null;

        super.append(c);

        return this;

    }

    @Override

    public synchronized StringBuffer append(int i) {

        toStringCache = null;

        super.append(i);

        return this;

    }

    /**

     * @since 1.5

     */

    @Override

    public synchronized StringBuffer appendCodePoint(int codePoint) {

        toStringCache = null;

        super.appendCodePoint(codePoint);

        return this;

    }

    @Override

    public synchronized StringBuffer append(long lng) {

        toStringCache = null;

        super.append(lng);

        return this;

    }

    @Override

    public synchronized StringBuffer append(float f) {

        toStringCache = null;

        super.append(f);

        return this;

    }

    @Override

    public synchronized StringBuffer append(double d) {

        toStringCache = null;

        super.append(d);

        return this;

    }

    /**

     * @throws StringIndexOutOfBoundsException {@inheritDoc}

     * @since      1.2

     */

    @Override

    public synchronized StringBuffer delete(int start, int end) {

        toStringCache = null;

        super.delete(start, end);

        return this;

    }

    /**

     * @throws StringIndexOutOfBoundsException {@inheritDoc}

     * @since      1.2

     */

    @Override

    public synchronized StringBuffer deleteCharAt(int index) {

        toStringCache = null;

        super.deleteCharAt(index);

        return this;

    }

    /**

     * @throws StringIndexOutOfBoundsException {@inheritDoc}

     * @since      1.2

     */

    @Override

    public synchronized StringBuffer replace(int start, int end, String str) {

        toStringCache = null;

        super.replace(start, end, str);

        return this;

    }

    /**

     * @throws StringIndexOutOfBoundsException {@inheritDoc}

     * @since      1.2

     */

    @Override

    public synchronized String substring(int start) {

        return substring(start, count);

    }

    /**

     * @throws IndexOutOfBoundsException {@inheritDoc}

     * @since      1.4

     */

    @Override

    public synchronized CharSequence subSequence(int start, int end) {

        return super.substring(start, end);

    }

    /**

     * @throws StringIndexOutOfBoundsException {@inheritDoc}

     * @since      1.2

     */

    @Override

    public synchronized String substring(int start, int end) {

        return super.substring(start, end);

    }

    /**

     * @throws StringIndexOutOfBoundsException {@inheritDoc}

     * @since      1.2

     */

    @Override

    public synchronized StringBuffer insert(int index, char[] str, int offset,

                                            int len)

    {

        toStringCache = null;

        super.insert(index, str, offset, len);

        return this;

    }

    /**

     * @throws StringIndexOutOfBoundsException {@inheritDoc}

     */

    @Override

    public synchronized StringBuffer insert(int offset, Object obj) {