第5章继承和多态5.1继承5.2Java的继承1：abstractclassPhoneCard2：{3：doublebalance;4：5：abstractbooleanperformDial();6：doublegetBalance()7：{8：returnbalance;9：}10：}11：abstractclassNone-Number-PhoneCardextendsPhoneCard12：{13：StringphoneSetType;14：15：StringgetSetType()16：{17：returnphoneSetType;18：}19：}20：abstractclassNumber-PhoneCardextendsPhoneCard21：{22：longcardNumber;23：intpassword;24：StringconnectNumber;25：booleanconnected;26：27：booleanperformConnection(longcn,intpw)28：{29：if(cn==cardNumber&&pw==password)30：{31：connected=true;32：returntrue;33：}34：else35：returnfalse;36：}37：}38：classmagCardextendsNone-Number-PhoneCard39：{40：StringusefulArea;41：42：booleanperformDial()43：{44：if(balance>0.9)45：{46：balance-=0.9;47：returntrue;48：}49：else50：returnfalse;51：}52：}53：classIC-CardextendsNone-Number-PhoneCard54：{55：booleanperformDial()56：{57：if(balance>0.5)58：{59：balance-=0.9;60：returntrue;61：}62：else63：returnfalse;64：}65：}66：classIP-CardextendsNumber-PhoneCard67：{68：DateexpireDate;69：booleanperformDial()70：{71：if(balance>0.3&&expireDate.after(newDate()))72：{73：balance-=0.3;74：returntrue;75：}76：else77：returnfalse;78：}79：}80：classD200-CardextendsNumber-PhoneCard81：{82：doubleadditoryFee;83：84：booleanperformDial()85：{86：if(balance>(0.5+additoryFee))87：{88：balance-=(0.5+additoryFee);89：returntrue;90：}91：else92：returnfalse;93：}94：}IP-Card类：doublebalance;//继承自父类Number-PhoneCardlongcardNumber;//继承自父类Number-PhoneCardintpassword;//继承自父类Number-PhoneCardStringconnectNumber;//继承自父类Number-PhoneCardbooleanconnect;//继承自父类Number-PhoneCardDateexpireDate;D200-Card类：doublebalance;//继承自父类Number-PhoneCardlongcardNumber;//继承自父类Number-PhoneCardintpassword;//继承自父类Number-PhoneCardStringconnectNumber;//继承自父类Number-PhoneCardbooleanconnect;//继承自父类Number-PhoneCarddoubleadditoryFee;增加定义了一个与从父类那里继承来的balance变量完全相同的变量。这样修改后，D