jdk源码阅读-stringbuffer类

public final class 
   extends AbstractStringBuilder
   implements java.io.Serializable, CharSequence

public () {
    super(16);
}

public synchronized StringBuffer append(Object obj) {
        super.append(String.valueOf(obj));
        return this;
}

public AbstractStringBuilder append(String str) {
       if (str == null) str = "null";
       int len = str.length();
       ensureCapacityInternal(count + len);
       str.getChars(0, len, value, count);
       count += len;
       return this;
   }

void expandCapacity(int minimumCapacity) {
      int newCapacity = value.length * 2 + 2;
      if (newCapacity - minimumCapacity < 0)
          newCapacity = minimumCapacity;
      if (newCapacity < 0) {
          if (minimumCapacity < 0) 
              throw new OutOfMemoryError();
          newCapacity = Integer.MAX_VALUE;
      }
      value = Arrays.copyOf(value, newCapacity);
  }