package org.apidesign.samples;

 import java.util.ArrayList;

 import java.util.List;

 public class StringBuffer {

     private List<String> all = new ArrayList<String>();

     public StringBuffer() {

         // prevent subclassing from 3rd party code

         if (getClass() != StringBuffer.class && getClass() != StringBufferUnsynch.class) {

             throw new IllegalStateException();

         }

     }

     // BEGIN: string.buffer.factory

     public static StringBuffer createUnsynchronized() {

         return new StringBufferUnsynch();

     }

     // END: string.buffer.factory

     public synchronized StringBuffer append(String s) {

         return appendImpl(s);

     }

     @Override

     public synchronized String toString() {

         return toStringImpl();

     }

     final String toStringImpl() {

         String ret = "";

         for (String s : all) {

             ret += s;

         }

         return ret;

     }

     final StringBuffer appendImpl(String s) {

         all.add(s);

         return this;

     }

     private static final class StringBufferUnsynch extends StringBuffer {

         @Override

         public StringBuffer append(String s) {

             return appendImpl(s);

         }

         @Override

         public String toString() {

             return toStringImpl();

         }

     }

 }