obtain the key for this node . concode_field_sep FibonacciHeapNode<T> parent concode_elem_sep T data concode_elem_sep FibonacciHeapNode<T> left concode_elem_sep int degree concode_elem_sep FibonacciHeapNode<T> right concode_elem_sep boolean mark concode_elem_sep double key concode_elem_sep FibonacciHeapNode<T> child concode_field_sep String toString concode_elem_sep T getData
double function ( ) { return key ; }