Cellular and wireless communication, portable computers, and satellite services promise to make it possible for mobile users to have access to information anywhere and anytime. However, mobile computing is characterized by many constraints. Any feasible approach to mobile computing must strike a balance between competing issues. This balance cannot be static as the environment of mobile computing changes; it must react, or in other words, the clients must be adaptive. We propose an approach for adaptive mobile applications based on mobile code and report on our experience in the context of one resource-intense application, an MP3 player. The results show that both increased application performance and reductions in power consumption are possible under certain conditions by shipping the resource-intensive decoding to the less constraint access network.