计算机英语 教学课件 作者 杨芸 主编 杨 蕾 李连弟 副主编unit7.ppt

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1、UnitsevenTheJavaLanguageTheJavaLanguageTheJavalanguageisaremarkableexampleofprogramminglanguageevolution.JavabuildsonthefamiliarandusefulfeaturesofC++whileremovingitscomplex，dangerous，andsuperfluouselements.Theresultisalanguagethatissafer，simpler，andeasiertouse.Thefollowingsection

2、sdescribeJavaincontrasttoC++.JavaIsFamiliarandSimpleIfyouhaveeverprogrammedinC++，youwillfindJava’sappealtobeinstantaneous.SinceJava’ssyntaxmirrorsthatofC++，youwillbeabletowriteJavaprogramswithinminutes.Yourfirstprogramswillcomequicklyandeasily，withverylittleprogrammingoverhead.You

3、willhavethefeelingthatyouhaveeliminatedalotofclutterfromyourprogramsandyouwillhave.AllthecrypticheaderfilesandpreprocessorstatementsofandC++aregone.Allthearcane#define1statementsandtypedefs2havebeentakenaway.Youwillnolongerhavetodelvethroughseverallevelsofheaderfilestocorrectlyref

4、erenceAPIcalls.Andnoonewillhavetosuffertofigureouthowtouseyoursoftware.Javaprogramssimplyimportthesoftwarepackagestheyneed.Thesepackagesmaybeinanotherdirectory，onanotherdrive，oronamachineontheothersideoftheInternet.TheJavacompilerandinterpreterfigureoutwhatobjectsarereferencedands

5、upplythenecessarylinkage.JavaIsObject---OrientedIfyouthinkC++isandobject-orientedprogramminglanguage，youareinforabigsurprise.AfterusingJavatowriteafewprograms，you’llgetabetterfeelingforwhatobject-orientedsoftwareisallabout.IknowIdid.Javadealswithclassesandobjects，pureandsimple4.Th

6、eyaren’tjustmoredatastructuresthatareavailabletotheprogrammer---theyarethebasisfortheentireprogramminglanguage.InC++，youcandeclareaclass，butyoudon’thaveto.YoucandeclareassociatedvariablesandusethemwithC-stylefunctions.InJava，classesandobjectsareatthecenterofthelanguage.Everythinge

7、lserevolvesaroundthem.Youcan’tdeclarefunctionsandprocedures.Theydon’texist.Youcan’tusestructures，unions，ortypedefs.They’regone，too.Youeitheruseclassesandobjectsoryoudon’tuseJava.It’sthatsimple.Javaprovidesalltheluxuriesofobject-orientedprogramming：classhierarchy，inheritance，encaps

8、ulation，andpolymorphisminacontext