参考答案

正确答案：clas s Bus extends Vehicle{private String driver；public Bus(String driver)f//A"convenience constructorH that defaults all the//parameters except for driver name．The"this"//Says create a bus passing the 4 default parameter//values plus the driver name to the other{/constructor for the Bus class．this("GM""Metro"42"Siiver"driver)；}public Bus(String mkString mdlint maxOccString clrString driver){//super says create a vehicle instance for this bus//super invokes the vehicle(superclass)constructorsuper(mkmdlmaxOccclr)；//We also need to store the name of the bus driver．//this．driver refers to the private instance variable//that has the same name as the constructor parameter this．driver=driver；}publ ic String getDriver(){return driver；}public void setDriver(String driver){this．driver=driver；}publ ic static void main(String[]args){//A main method for testing use onlyBus firstBus=new Bus("Joe")；Bus secondBus=new Bus("Mercedes""B302"60"Black" "Mary")；System．out．println("First bus："+firstBus．getMake()+"driven by"+firstBus．getDriver())；System．out．println("Second bus："+secondBus．getMake()+"driven by"+secondBus．getDriver())；secondBus．setDriver("David")；System．out．println("Second bus："+secondBus．getMake()+"driven by"+secondBus．getDriver())；}}
classBusextendsVehicle{privateStringdriver；publicBus(Stringdriver)f//A"convenienceconstructorHthatdefaultsallthe//parametersexceptfordrivername．The"this"//Sayscreateabuspassingthe4defaultparameter//values,plusthedrivername,totheother{/constructorfortheBusclass．this("GM","Metro",42,"Siiver",driver)；}publicBus(Stringmk,Stringmdl,intmaxOcc,Stringclr,Stringdriver){//supersayscreateavehicleinstanceforthisbus//superinvokesthevehicle(superclass)constructorsuper(mk,mdl,maxOcc,clr)；//Wealsoneedtostorethenameofthebusdriver．//this．driverreferstotheprivateinstancevariable//thathasthesamenameastheconstructorparameterthis．driver=driver；}publicStringgetDriver(){returndriver；}publicvoidsetDriver(Stringdriver){this．driver=driver；}publicstaticvoidmain(String[]args){//AmainmethodfortestinguseonlyBusfirstBus=newBus("Joe")；BussecondBus=newBus("Mercedes","B302",60,"Black","Mary")；System．out．println("Firstbus："+firstBus．getMake()+"drivenby"+firstBus．getDriver())；System．out．println("Secondbus："+secondBus．getMake()+"drivenby"+secondBus．getDriver())；secondBus．setDriver("David")；System．out．println("Secondbus："+secondBus．getMake()+"drivenby"+secondBus．getDriver())；}}