Hello everyone !
So, I need for a particular reason to convert the key value returned by the keyPressed() function to a string. Here is the code ;

import ddf.minim.*;

Minim _minim;
HashMap _soundBox;

void setup(){
 size(100, 100);

 _minim = new Minim(this);
 _soundBox = new HashMap();

 //get the data folder on my sketch
 java.io.File folder = new java.io.File(dataPath(""));
 java.io.FilenameFilter wavFilter = new java.io.FilenameFilter() {
   boolean accept(File dir, String name) {

     //returned all wav files
     return name.endsWith(".wav");  
   }
 };

 //populate an array for the returned values
 String[] filenames = folder.list(wavFilter);

 //populate an Hashmap with the first letter of the files for key and the filename for value
 for (int i = 0; i < filenames.length; i++) {
   _soundBox.put(filenames[i].substring(0,1), filenames[i]);
 }

 //unmark the next block if you need to understand
 /*
 Iterator i = _soundBox.entrySet().iterator();
  while (i.hasNext()) {
  Map.Entry me = (Map.Entry)i.next();
  println(me.getKey() + " is ");
  println(me.getValue());
  }
  */
}

void draw(){
 background(0);
}

//THE PROBLEM
void keyPressed(){
 //this method returns an error "Cannot cast from char to String"
 println((String)key);
 
 //this one too... "Cannot invoke tostring() on the primitive type char"
 println(key.tostring());
 
 //return null
 println("#Hashmap for " + key + "# >> "+_soundBox.get(key));
 
 //return the proper value assuming you have a wav file that begins with "q"
 println("#Hashmap for q# >>"+_soundBox.get("q"));
}

If I need this, it's because each one of my "wav files" begin with a specific letter that I want to link with the keyressed() function. So, if I would like to link more files with a keyPressed event, I just would have to rename the file with the key I wish ("gpianosample.wav", for example), without touching anything inside the program.

Hope that first post will be answered. (hope you understand my english too...)

either use:
http://processing.org/reference/str_.html

or just:
println( key + "" );  // will be cast to String automatically

F