public String toString(){
  StringBuilder s=new StringBuilder();
  for (  int i : st.keys()) {
    s.append("(" + i + ", "+ st.get(i)+ ") ");
  }
  return s.toString();
}

public String toString ( ) { StringBuilder s = new StringBuilder ( ) ; for ( int i : st . keys ( ) ) { s . append ( "(" + i + ", " + st . get ( i ) + ") " ) ; } return s . toString ( ) ; }
returns a string representation of this vector .
