content: /*
   * 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     StringBuilder
   * @see     String
   * @since   JDK1.0
   */
   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) {
          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) {
          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) {
          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   JDK1.0.2
       */
      @Override
      public synchronized StringBuffer reverse() {
          toStringCache = null;
          super.reverse();
          return this;
      }
  
      @Override
      public synchronized String toString() {
          if (toStringCache == null) {
              toStringCache = Arrays.copyOfRange(value, 0, count);
          }
          return new String(toStringCache, 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);
      }
  }
  