Superclass of Phone, subclass of Object. Any class that does not explicitly extend another class is a subclass of Object.

public class Device {
	private Battery b;
	
//	public Device() {
//	}
	
	public Device(Battery b) {
		this.b = b;
	}
	
	public double getVoltage() {
		return b.getVoltage();
	}
	
	public Battery getBattery() {
		return b;
	}
}