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 package org.apidesign.delegatingwriter;

 import java.io.BufferedWriter;

 import java.io.IOException;

 import java.io.Writer;

 /**

  * This is a regular {@link BufferedWriter}, just its implementation

  * of the append method can choose from three options. This allows us to

  * simulate the potential pros and cons of various possible implementations.

  * 

  * @author Jaroslav Tulach <jaroslav.tulach@apidesign.org>

  */

 public class AltBufferedWriter extends BufferedWriter {

     private final Writer out;

     private final Behaviour behaviour;

     public AltBufferedWriter(Writer out) {

         // behave exactly like BufferedWriter in 1.5 behaves

         this(out, Behaviour.DELEGATE_TO_SUPER);

     }

     public AltBufferedWriter(Writer out, Behaviour behaviour) {

         super(out);

         this.out = out;

         this.behaviour = behaviour;

     }

     @Override

     public Writer append(CharSequence csq) throws IOException {

         switch (behaviour) {

             case THROW_EXCEPTION: return appendThrowException(csq); 

             case DELEGATE_TO_SUPER: return appendDelegateToSuper(csq);

             case DELEGATE_TO_OUT: return appendDelegateToUnderlaying(csq);

             case DELEGATE_CONDITIONALLY: return appendDelegateConditionally(csq);

             default: throw new IllegalStateException("Unknown" + behaviour);

         }

     }

     public Writer appendThrowException(CharSequence csq) throws IOException {

         /* in case of real code, this would be part of the regular append method BEGIN: writer.throw

     public Writer append(CharSequence csq) throws IOException {

         /* thrown an exception as this method is new and subclasses need to override it */

         throw new UnsupportedOperationException();

     }

     // END: writer.throw

     public Writer appendDelegateToSuper(CharSequence csq) throws IOException {

         // non-efficient variant of delegating via converting to String first 

         // and using one of methods that existed in 1.4

         // BEGIN: writer.throw.client

         if (csq == null) {

             write("null");

         } else {

             write(csq.toString());

         }

         return this;

         // END: writer.throw.client

     }

     public Writer appendDelegateToUnderlaying(CharSequence csq) throws IOException {

         // BEGIN: writer.delegateout

         // efficient, yet dangerous delegation skipping methods unknown to 

         // subclasses that used version 1.4

         out.append(csq);

         return this;

         // END: writer.delegateout

     }

     private Writer appendDelegateConditionally(CharSequence csq) throws IOException {

         // BEGIN: writer.conditionally

         boolean isOverriden = false;

         try {

             isOverriden = 

                 (getClass().getMethod("write", String.class).getDeclaringClass() != Writer.class) ||

                 (getClass().getMethod("write", Integer.TYPE).getDeclaringClass() != BufferedWriter.class) ||

                 (getClass().getMethod("write", String.class, Integer.TYPE, Integer.TYPE).getDeclaringClass() != BufferedWriter.class);

         } catch (Exception ex) {

             throw new IOException(ex);

         }

         if (isOverriden) {

             if (csq == null) {

                 write("null");

             } else {

                 write(csq.toString());

             }

         } else {

             out.append(csq);

         }

         return this;

         // END: writer.conditionally

     }

     public enum Behaviour {

         THROW_EXCEPTION, DELEGATE_TO_SUPER, DELEGATE_TO_OUT, DELEGATE_CONDITIONALLY

     }

 }