java 源码 StringBuffer

 /*
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  * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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 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.
  *
  * 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.
  *
  * The principal operations on a StringBuffer are the
  * append and 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
  * append method always adds these characters at the end
  * of the buffer; the insert method adds the characters at
  * a specified point.
  *
  * For example, if z refers to a string buffer object
  * whose current contents are "start", then
  * the method call z.append("le") would cause the string
  * buffer to contain "startle", whereas
  * z.insert(4, "le") would alter the string buffer to
  * contain "starlet".
  *
  * In general, if sb refers to an instance of a StringBuffer,
  * then sb.append(x) has the same effect as
  * sb.insert(sb.length(), x).
  *
  * 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.
  *
  * 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
  * 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   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 capacity
      *               argument is less than 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
      * 16 plus the length of the string argument.
      *
      * @param   str   the initial contents of the buffer.
      * @exception NullPointerException if str is null
      */
     public StringBuffer(String str) {
         super(str.length() + 16);
         append(str);
     }

     /**
      * Constructs a string buffer that contains the same characters
      * as the specified CharSequence. The initial capacity of
      * the string buffer is 16 plus the length of the
      * CharSequence argument.
      *
      * If the length of the specified CharSequence is
      * less than or equal to zero, then an empty buffer of capacity
      * 16 is returned.
      *
      * @param      seq   the sequence to copy.
      * @exception NullPointerException if seq is null
      * @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 StringBuffer to this sequence.
      *
      * The characters of the StringBuffer argument are appended,
      * in order, to the contents of this StringBuffer, increasing the
      * length of this StringBuffer by the length of the argument.
      * If sb is null, then the four characters
      * "null" are appended to this StringBuffer.
      *
      * Let n be the length of the old character sequence, the one
      * contained in the StringBuffer just prior to execution of the
      * append method. Then the character at index k in
      * the new character sequence is equal to the character at index k
      * in the old character sequence, if k is less than n;
      * otherwise, it is equal to the character at index k-n in the
      * argument sb.
      *
      * This method synchronizes on this (the destination)
      * object but does not synchronize on the source (sb).
      *
      * @param   sb   the StringBuffer 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 CharSequence to this
      * sequence.
      *
      * The characters of the CharSequence argument are appended,
      * in order, increasing the length of this sequence by the length of the
      * argument.
      *
      * The result of this method is exactly the same as if it were an
      * invocation of this.append(s, 0, s.length());
      *
      * This method synchronizes on this (the destination)
      * object but does not synchronize on the source (s).
      *
      * If s is null, then the four characters
      * "null" are appended.
      *
      * @param   s the CharSequence 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);
     }
 }