/*
- * Copyright (c) 1994, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1994, 2021, 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.io.IOException;
-import java.util.Arrays;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.io.ObjectStreamField;
+import java.io.Serial;
+import java.io.Serializable;
+import java.io.StreamCorruptedException;
 import jdk.internal.vm.annotation.IntrinsicCandidate;
 
 /**
  * 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.
  *
  * @apiNote
  * {@code StringBuffer} implements {@code Comparable} but does not override
  * {@link Object#equals equals}. Thus, the natural ordering of {@code StringBuffer}
  * is inconsistent with equals. Care should be exercised if {@code StringBuffer}
  * objects are used as keys in a {@code SortedMap} or elements in a {@code SortedSet}.
  * See {@link Comparable}, {@link java.util.SortedMap SortedMap}, or
  * {@link java.util.SortedSet SortedSet} for more information.
  *
  * @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, Comparable<StringBuffer>, CharSequence
+    implements Serializable, Comparable<StringBuffer>, CharSequence
 {
 
     /**
      * A cache of the last value returned by toString. Cleared
      * whenever the StringBuffer is modified.
      */
     private transient String toStringCache;
 
     /** use serialVersionUID from JDK 1.0.2 for interoperability */
-    @java.io.Serial
+    @Serial
     static final long serialVersionUID = 3388685877147921107L;
 
     /**
      * Constructs a string buffer with no characters in it and an
      * initial capacity of 16 characters.
      */
     @IntrinsicCandidate
     public StringBuffer() {
         super(16);
     }
 
     /**
      * Constructs a string buffer with no characters in it and
      * the specified initial capacity.
      *
      * @param      capacity  the initial capacity.
      * @throws     NegativeArraySizeException  if the {@code capacity}
      *             argument is less than {@code 0}.
      */
     @IntrinsicCandidate
     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.
      */
     @IntrinsicCandidate
     public StringBuffer(String str) {
         super(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.
      *
      * @param      seq   the sequence to copy.
      * @since 1.5
      */
     public StringBuffer(CharSequence seq) {
         super(seq);
     }
 
     /**
      * Compares two {@code StringBuffer} instances lexicographically. This method
      * follows the same rules for lexicographical comparison as defined in the
      * {@linkplain java.lang.CharSequence#compare(java.lang.CharSequence,
      * java.lang.CharSequence)  CharSequence.compare(this, another)} method.
      *
      * <p>
      * For finer-grained, locale-sensitive String comparison, refer to
      * {@link java.text.Collator}.
      *
      * @implNote
      * This method synchronizes on {@code this}, the current object, but not
      * {@code StringBuffer another} with which {@code this StringBuffer} is compared.
      *
      * @param another the {@code StringBuffer} to be compared with
      *
      * @return  the value {@code 0} if this {@code StringBuffer} contains the same
      * character sequence as that of the argument {@code StringBuffer}; a negative integer
      * if this {@code StringBuffer} is lexicographically less than the
      * {@code StringBuffer} argument; or a positive integer if this {@code StringBuffer}
      * is lexicographically greater than the {@code StringBuffer} argument.
      *
      * @since 11
      */
     @Override
     public synchronized int compareTo(StringBuffer another) {
         return super.compareTo(another);
     }
 
     @Override
     public synchronized int length() {
         return count;
     }
 
     @Override
     public synchronized int capacity() {
         return super.capacity();
     }
 
 
     @Override
     public synchronized void ensureCapacity(int minimumCapacity) {
         super.ensureCapacity(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) {
         return super.charAt(index);
     }
 
     /**
      * @throws IndexOutOfBoundsException {@inheritDoc}
      * @since      1.5
      */
     @Override
     public synchronized int codePointAt(int index) {
         return super.codePointAt(index);
     }
 
     /**
      * @throws IndexOutOfBoundsException {@inheritDoc}
      * @since     1.5
      */
     @Override
     public synchronized int codePointBefore(int index) {
         return super.codePointBefore(index);
     }
 
     /**
      * @throws IndexOutOfBoundsException {@inheritDoc}
      * @since     1.5
      */
     @Override
     public synchronized int codePointCount(int beginIndex, int endIndex) {
         return super.codePointCount(beginIndex, endIndex);
     }
 
     /**
      * @throws IndexOutOfBoundsException {@inheritDoc}
      * @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) {
         toStringCache = null;
         super.setCharAt(index, ch);
     }
 
     @Override
     public synchronized StringBuffer append(Object obj) {
         toStringCache = null;
         super.append(String.valueOf(obj));
         return this;
     }
 
     @Override
     @IntrinsicCandidate
     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
     @IntrinsicCandidate
     public synchronized StringBuffer append(char c) {
         toStringCache = null;
         super.append(c);
         return this;
     }
 
     @Override
     @IntrinsicCandidate
     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) {
         toStringCache = null;
         super.insert(offset, String.valueOf(obj));
         return this;
     }
 
     /**
      * @throws StringIndexOutOfBoundsException {@inheritDoc}
      */
     @Override
     public synchronized StringBuffer insert(int offset, String str) {
         toStringCache = null;
         super.insert(offset, str);
         return this;
     }
 
     /**
      * @throws StringIndexOutOfBoundsException {@inheritDoc}
      */
     @Override
     public synchronized StringBuffer insert(int offset, char[] str) {
         toStringCache = null;
         super.insert(offset, str);
         return this;
     }
 
     /**
      * @throws IndexOutOfBoundsException {@inheritDoc}
      * @since      1.5
      */
     @Override
     public StringBuffer insert(int dstOffset, CharSequence s) {
         // Note, synchronization achieved via invocations of other StringBuffer methods
         // after narrowing of s to specific type
         // Ditto for toStringCache clearing
         super.insert(dstOffset, s);
         return this;
     }
 
     /**
      * @throws IndexOutOfBoundsException {@inheritDoc}
      * @since      1.5
      */
     @Override
     public synchronized StringBuffer insert(int dstOffset, CharSequence s,
             int start, int end)
     {
         toStringCache = null;
         super.insert(dstOffset, s, start, end);
         return this;
     }
 
     /**
      * @throws StringIndexOutOfBoundsException {@inheritDoc}
      */
     @Override
     public  StringBuffer insert(int offset, boolean b) {
         // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
         // after conversion of b to String by super class method
         // Ditto for toStringCache clearing
         super.insert(offset, b);
         return this;
     }
 
     /**
      * @throws IndexOutOfBoundsException {@inheritDoc}
      */
     @Override
     public synchronized StringBuffer insert(int offset, char c) {
         toStringCache = null;
         super.insert(offset, c);
         return this;
     }
 
     /**
      * @throws StringIndexOutOfBoundsException {@inheritDoc}
      */
     @Override
     public StringBuffer insert(int offset, int i) {
         // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
         // after conversion of i to String by super class method
         // Ditto for toStringCache clearing
         super.insert(offset, i);
         return this;
     }
 
     /**
      * @throws StringIndexOutOfBoundsException {@inheritDoc}
      */
     @Override
     public StringBuffer insert(int offset, long l) {
         // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
         // after conversion of l to String by super class method
         // Ditto for toStringCache clearing
         super.insert(offset, l);
         return this;
     }
 
     /**
      * @throws StringIndexOutOfBoundsException {@inheritDoc}
      */
     @Override
     public StringBuffer insert(int offset, float f) {
         // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
         // after conversion of f to String by super class method
         // Ditto for toStringCache clearing
         super.insert(offset, f);
         return this;
     }
 
     /**
      * @throws StringIndexOutOfBoundsException {@inheritDoc}
      */
     @Override
     public StringBuffer insert(int offset, double d) {
         // Note, synchronization achieved via invocation of StringBuffer insert(int, String)
         // after conversion of d to String by super class method
         // Ditto for toStringCache clearing
         super.insert(offset, d);
         return this;
     }
 
     /**
      * @since      1.4
      */
     @Override
     public int indexOf(String str) {
         // Note, synchronization achieved via invocations of other StringBuffer methods
         return super.indexOf(str);
     }
 
     /**
      * @since      1.4
      */
     @Override
     public synchronized int indexOf(String str, int fromIndex) {
         return super.indexOf(str, fromIndex);
     }
 
     /**
      * @since      1.4
      */
     @Override
     public int lastIndexOf(String str) {
         // Note, synchronization achieved via invocations of other StringBuffer methods
         return lastIndexOf(str, count);
     }
 
     /**
      * @since      1.4
      */
     @Override
     public synchronized int lastIndexOf(String str, int fromIndex) {
         return super.lastIndexOf(str, fromIndex);
     }
 
     /**
      * @since   1.0.2
      */
     @Override
     public synchronized StringBuffer reverse() {
         toStringCache = null;
         super.reverse();
         return this;
     }
 
     @Override
     @IntrinsicCandidate
     public synchronized String toString() {
         if (toStringCache == null) {
             return toStringCache =
                     isLatin1() ? StringLatin1.newString(value, 0, count)
                                : StringUTF16.newString(value, 0, count);
         }
         return new String(toStringCache);
     }
 
     /**
      * 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.
      */
-    @java.io.Serial
-    private static final java.io.ObjectStreamField[] serialPersistentFields =
+    @Serial
+    private static final ObjectStreamField[] serialPersistentFields =
     {
-        new java.io.ObjectStreamField("value", char[].class),
-        new java.io.ObjectStreamField("count", Integer.TYPE),
-        new java.io.ObjectStreamField("shared", Boolean.TYPE),
+        new ObjectStreamField("value", char[].class),
+        new ObjectStreamField("count", Integer.TYPE),
+        new ObjectStreamField("shared", Boolean.TYPE),
     };
 
     /**
-     * The {@code writeObject} method is called to write the state of the {@code StringBuffer} to
-     * a stream.
+     * The {@code writeObject} method is called to write the state of the
+     * {@code StringBuffer} to a stream.
      *
      * @param  s the {@code ObjectOutputStream} to which data is written
      * @throws IOException if an I/O error occurs
      */
-    @java.io.Serial
-    private synchronized void writeObject(java.io.ObjectOutputStream s)
-        throws java.io.IOException {
-        java.io.ObjectOutputStream.PutField fields = s.putFields();
+    @Serial
+    private synchronized void writeObject(ObjectOutputStream s)
+            throws IOException {
+        ObjectOutputStream.PutField fields = s.putFields();
         char[] val = new char[capacity()];
         if (isLatin1()) {
             StringLatin1.getChars(value, 0, count, val, 0);
         } else {
             StringUTF16.getChars(value, 0, count, val, 0);
         }
         fields.put("value", val);
         fields.put("count", count);
         fields.put("shared", false);
         s.writeFields();
     }
 
     /**
-     * The {@code readObject} method is called to restore the state of the {@code StringBuffer} from
-     * a stream.
+     * The {@code readObject} method is called to restore the state of the
+     * {@code StringBuffer} from a stream.
      *
      * @param  s the {@code ObjectInputStream} from which data is read
      * @throws IOException if an I/O error occurs
      * @throws ClassNotFoundException if a serialized class cannot be loaded
      */
-    @java.io.Serial
-    private void readObject(java.io.ObjectInputStream s)
-        throws java.io.IOException, ClassNotFoundException {
-        java.io.ObjectInputStream.GetField fields = s.readFields();
+    @Serial
+    private void readObject(ObjectInputStream s)
+        throws IOException, ClassNotFoundException {
+        ObjectInputStream.GetField fields = s.readFields();
+
         char[] val = (char[])fields.get("value", null);
+        int c = fields.get("count", 0);
+        if (c < 0 || c > val.length) {
+            throw new StreamCorruptedException("count value invalid");
+        }
         initBytes(val, 0, val.length);
-        count = fields.get("count", 0);
+        count = c;
+        // ignore shared field
     }
 
-    synchronized void getBytes(byte dst[], int dstBegin, byte coder) {
+    synchronized void getBytes(byte[] dst, int dstBegin, byte coder) {
         super.getBytes(dst, dstBegin, coder);
     }
 }