参考答案

正确答案：private double totalFuel=0．；private double totalMiles=0．；public void reFuel(double fueiQuantitydouble milesSinceLastFueling){totalMiles+=milesSinceLastFueling；totalFuel+=fuelQuantity；}publ ic double fuelEconomy(){return tota]Miles/totalFuel；}在Skateboard的实例上调用refuel方法时应做如下工作：class Skateboard extends Vehicle{public Skateboard(String mkString mdlString clr){super(mkmdl1clr)；}public double changeSpeed(double newSpeed){if(newSpeed>10．){newSpeed=10．；}double accel=newSpeed-this．getSpeed()；thiS．setSpeed(newSpeed)；return accel ；}publiC double fuelEconomy()throws UnsupportedOperationException{throw new UnsupportedOperationException("Skateboard Uses no fuel")；}public void reFuel(double gallonsdouble miles)throws UnsupportedOperationException{throw new UnsupportedOperationException("Skateboard uSes no fuel")；}}ManyVehicles的测试类:public clasS ManyVehicles{//main method：testS the VehiCle classpublic static void main(String[]args){Vehicle vlv2v3v4；vl=new Vehicle("Ford""MuStanq"2"red")；v2=new Vehicle("BMW""328i"4"silver")；v3=new Vehicle("Chrysler""PT Cruiser"4"gold")；System．out．println("There are"+Vehicle．VehicleCount+"vehicles．")；System．out．println(”Make of vl(Ford)："+V1．getMake())；System．out．println("Model of v2(328i)："+v2．getModel())；System．out．printin("Col．or of v3(gold："+v3．getColor())；System．out．println("Max occupants of v1(2)："+v1．getMaxOccupants())；double accel=v1．changeSpeed(70．)；System．out．println(v1．getModel()+"accelerated by"+accel+"mph to”+v1．getSpeed()+"mph．")；v1．setMake("Chevrolet")；v1．setModel("Malibu")；v1．setColor("white")；v1．setSpeed(60．)；System．out．println("v1 is now a"+v1．getColor()+""+v1．getMake()+""+v1．getModel()+"going”+v1．getSpeed()+"mph．")；v4=new Skateboard("Mako""Shark""red")；accel=v4．changeSpeed(5．)；System．out．println(”v4 is a"+v4．getMake()+""+v4．getModel()+""+v4．getColor()+"skateboard going"+v4．getSpeed()+"mph．")；accel=v4．changeSpeed(22．)；System．out．println("The Skateboard is now going"+v4．getSpeed()+"mph．")；v2．reFuel(11．3295．) //should be 2 6．1 mpgSystem．out．println("The"+v2．getMake()+"mileage："+v2．fuelEconomy())；try{System．outprintln ("Refueling skateboard")v4refuel(0．5．)；}catch(Exception e}{System．out．println(e．getMessaqe())；}}}
privatedoubletotalFuel=0．；privatedoubletotalMiles=0．；publicvoidreFuel(doublefueiQuantity,doublemilesSinceLastFueling){totalMiles+=milesSinceLastFueling；totalFuel+=fuelQuantity；}publicdoublefuelEconomy(){returntota]Miles/totalFuel；}在Skateboard的实例上调用refuel方法时,应做如下工作：classSkateboardextendsVehicle{publicSkateboard(Stringmk,Stringmdl,Stringclr){super(mk,mdl,1,clr)；}publicdoublechangeSpeed(doublenewSpeed){if(newSpeed>10．){newSpeed=10．；}doubleaccel=newSpeed-this．getSpeed()；thiS．setSpeed(newSpeed)；returnaccel；}publiCdoublefuelEconomy()throwsUnsupportedOperationException{thrownewUnsupportedOperationException("SkateboardUsesnofuel")；}publicvoidreFuel(doublegallons,doublemiles)throwsUnsupportedOperationException{thrownewUnsupportedOperationException("SkateboarduSesnofuel")；}}ManyVehicles的测试类:publicclasSManyVehicles{//mainmethod：testStheVehiCleclasspublicstaticvoidmain(String[]args){Vehiclevl,v2,v3,v4；vl=newVehicle("Ford","MuStanq",2,"red")；v2=newVehicle("BMW","328i",4,"silver")；v3=newVehicle("Chrysler","PTCruiser",4,"gold")；System．out．println("Thereare"+Vehicle．VehicleCount+"vehicles．")；System．out．println(”Makeofvl(Ford)："+V1．getMake())；System．out．println("Modelofv2(328i)："+v2．getModel())；System．out．printin("Col．orofv3(gold："+v3．getColor())；System．out．println("Maxoccupantsofv1(2)："+v1．getMaxOccupants())；doubleaccel=v1．changeSpeed(70．)；System．out．println(v1．getModel()+"acceleratedby"+accel+"mphto”+v1．getSpeed()+"mph．")；v1．setMake("Chevrolet")；v1．setModel("Malibu")；v1．setColor("white")；v1．setSpeed(60．)；System．out．println("v1isnowa"+v1．getColor()+""+v1．getMake()+""+v1．getModel()+"going”+v1．getSpeed()+"mph．")；v4=newSkateboard("Mako","Shark","red")；accel=v4．changeSpeed(5．)；System．out．println(”v4isa"+v4．getMake()+""+v4．getModel()+""+v4．getColor()+"skateboardgoing"+v4．getSpeed()+"mph．")；accel=v4．changeSpeed(22．)；System．out．println("TheSkateboardisnowgoing"+v4．getSpeed()+"mph．")；v2．reFuel(11．3,295．),//shouldbe26．1mpgSystem．out．println("The"+v2．getMake()+"mileage："+v2．fuelEconomy())；try{System．out,println("Refuelingskateboard"),v4,refuel(0．,5．)；}catch(Exceptione}{System．out．println(e．getMessaqe())；}}}