public class Directory extends Elm {
 private Elm[] contents;
 private int idx;
 public Directory (String name){
     super(name);
     contents = new Elm[100];
 }
 public void add(Elm e){
     if (idx < 100){
     contents[idx]=e;
     idx++;
      e.setParent(this);
     }
 }
public void show() {
    for (Elm e : contents)
        if (e != null)
            System.out.println(e.name);
 }
public Elm search(String name) {
  if (this.name.equals(name))
      return this;
  for (Elm e : contents)
      if (e!=null && e.name.equals(name))
          return e;
  for (Elm e : contents)
      if (e!=null && e instanceof Directory)
          if (((Directory)e).search(name)!=null)
              return e;
  return null;
 }
}