public class MyFormatter{
      private String buf;
      private Formatter outFile;
      private boolean append;
      private StringBuffer myBuf;

      public MyFormatter(Formatter outFile, boolean append){
           this.outFile = outFile;
           this.append = append;
           buf = use BufferedReader and InputStreamReader
             to read The String in the file and store
             it in buf
           myBuf = new StringBuffer(buf);
      }

      public boolean doAppend(String str){
            //  You are able to append
            if(append == true){
                 myBuf.append(str);
                 return true;
            }else{
                 //  We are not in append mode
                 return false;
            }
       }

       public String toString(){
            return myBuf.toString();
       }
}

   String globalString;//  initiated in Constructor

   //  Expensive method
   public String app(String str){
         globalString = globalString+str;
   }

   //  supposing you want to append a few hundred
   for(int i = 0; i < myStrings.length; i++){
         app(myStrings[i]);
    }
    
    //  In expensive method
    public String app(String str){
          myStringBuf.append(str);
    }
    //  using buffer algorithm
    for(int i = 0; i < myStrings.length; i++){
         app(myStrings[i]);
     }