java集合框架(習(xí)題和答案及解析)

...wd......wd......wd...java集合框架〔習(xí)題〕集合框架KeyPoint*Collection接口、Set接口、List接口基本操作*List接口及其實(shí)現(xiàn)類*Set接口及其實(shí)現(xiàn)類*迭代遍歷*Hash算法與hashCode方法*Comparable接口*Map接口及其實(shí)現(xiàn)類*遍歷Map*泛型練習(xí)1.填空Collection接口的特點(diǎn)是元素是對(duì)象；List接口的特點(diǎn)是元素有〔有|無〕順序，可以〔可以|不可以〕重復(fù)；Set接口的特點(diǎn)是元素?zé)o〔有|無〕順序，不可以〔可以|不可以〕重復(fù)；Map接口的特點(diǎn)是元素是鍵值對(duì)，其中值可以重復(fù)，鍵不可以重復(fù)。2.〔List〕有如下代碼importjava.util.*;publicclassTestList{publicstaticvoidmain(Stringargs[]){Listlist=newArrayList();list.add(“Hello〞);list.add(“World〞);list.add(1,“Learn〞);list.add(1,“Java〞);printList(list);}publicstaticvoidprintList(Listlist){for(Objectobj:list){Stringstr=(String)obj;System.out.println(obj);}}}要求：1)把//1處的代碼補(bǔ)充完整，要求輸出list中所有元素的內(nèi)容2)寫出程序執(zhí)行的結(jié)果HellojavaLearnWorld3)如果要把實(shí)現(xiàn)類由ArrayList換為L(zhǎng)inkedList，應(yīng)該改哪里ArrayList和LinkedList使用上有什么區(qū)別實(shí)現(xiàn)上有什么區(qū)別把實(shí)例化的語句改為newLinkedList();ArrayList數(shù)組實(shí)現(xiàn)查詢快增刪慢LinkedList鏈表實(shí)現(xiàn)查詢慢增刪快4)如果要把實(shí)現(xiàn)類由ArrayList換為Vector，應(yīng)該改哪里ArrayList和Vector使用上有什么區(qū)別實(shí)現(xiàn)上有什么區(qū)別ArrayList是線程不同步的，輕量級(jí)的，線程不安全，速度快Vector是線程同步的，多線程訪問對(duì)比安全，速度慢3.〔List〕寫出下面程序的運(yùn)行結(jié)果importjava.util.*;publicclassTestList{publicstaticvoidmain(Stringargs[]){Listlist=newArrayList();list.add(“Hello〞);list.add(“World〞);list.add(“Hello〞);list.add(“Learn〞);list.remove(“Hello〞);list.remove(0);for(inti=0;i<list.size();i++){System.out.println(list.get(i));}}}HelloLearn4.〔Set，List〕importjava.util.*;publicclassTestListSet{publicstaticvoidmain(Stringargs[]){Listlist=newArrayList();list.add(“Hello〞);list.add(“Learn〞);list.add(“Hello〞);list.add(“Welcome〞);Setset=newHashSet();set.addAll(list);System.out.println(set.size());}}選擇正確答案A．編譯不通過B．編譯通過，運(yùn)行時(shí)異常C．編譯運(yùn)行都正常，//輸出HashSet中不能放重復(fù)值D．編譯運(yùn)行都正常，輸出45.〔List〕有一個(gè)Worker類如下：publicclassWorker{privateintage;privateStringname;privatedoublesalary;publicWorker(){}publicWorker(Stringname,intage,doublesalary){=name;this.age=age;this.salary=salary;}publicintgetAge(){returnage;}publicvoidsetAge(intage){this.age=age;}publicStringgetName(){returnname;}publicvoidsetName(Stringname){=name;}publicdoublegetSalary(){returnsalary;}publicvoidsetSalary(doublesalary){this.salary=salary;}publicvoidwork(){System.out.println(name+“work〞);}}完成下面的要求1)創(chuàng)立一個(gè)List，在List中增加三個(gè)工人，基本信息如下：姓名年齡工資zhang3183000li4253500wang52232002)在li4之前插入一個(gè)工人，信息為：姓名：zhao6，年齡：24，工資33003)刪除wang5的信息4)利用for循環(huán)遍歷，打印List中所有工人的信息5)利用迭代遍歷，對(duì)List中所有的工人調(diào)用work方法。6)為Worker類添加equals方法6.〔Set，Hash算法〕為上一題的Worker類，在添加完equals方法的根基上，添加一個(gè)hashCode方法。publicinthashCode(){//1}有幾種寫法：1〕return0;2〕intresult=0;if(name!=null)result=name.hashCode();returnresult+age;3〕returnsuper.hashCode();現(xiàn)在要把Worker類放入HashSet中，并希望在HashSet中沒有重復(fù)元素，那么下面說法正確的是：A.三種寫法都正確B.1),2)寫法正確，2)效率更高C.2)寫法正確，1),3)寫法都不正確7.〔Set，Hash算法，方法覆蓋〕代碼改錯(cuò)importjava.util.*;classWorker{Stringname;intage;doublesalary;publicWorker(){}publicWorker(Stringname,intage,doublesalary){=name;this.age=age;this.salary=salary;}publicinthashCode(){//hashCode必須聲明為公共的。return〔int〕〔name.hashCode()+age+salary〕;//返回值類型為整形〔}//equals方法實(shí)現(xiàn)有錯(cuò)publicbooleanequals(Workerw){if(==name&&w.salary==salary&&w.age==age){returntrue;}elsereturnfalse;}}publicclassTestWorker{publicstaticvoidmain(Stringargs[]){Setset=newHashSet();set.add(newWorker(“tom〞,18,2000));set.add(newWorker(“tom〞,18,2000));set.add(0,newWorker(“jerry〞,18,2000));//HashSet中沒有定義帶下標(biāo)的add方法。System.out.println(set.size());}}8.〔Set，Hash算法〕在前面的Worker類根基上，為Worker類增加相應(yīng)的方法，使得Worker放入HashSet中時(shí)，Set中沒有重復(fù)元素。并編寫相應(yīng)的測(cè)試代碼。classWorker{Stringname;intage;doublesalary;publicWorker(){}publicWorker(Stringname,intage,doublesalary){=name;this.age=age;this.salary=salary;}publicinthashCode(){return〔int〕〔name.hashCode()+age+salary〕;}publicbooleanequals(Workerw){if(==name&&w.salary==salary&&w.age==age){returntrue;}elsereturnfalse;}}9.〔Set，Comparable接口〕在前面的Worker類根基上，為Worker類添加相應(yīng)的代碼，使得Worker對(duì)象能正確放入TreeSet中。并編寫相應(yīng)的測(cè)試代碼。注：對(duì)比時(shí)，先對(duì)比工人年齡大小，年齡小的排在前面。如果兩個(gè)工人年齡一樣，那么再對(duì)比其收入，收入少的排前面。如果年齡和收入都一樣，那么根據(jù)字典順序?qū)Ρ裙と诵彰＠纾河腥齻€(gè)工人，基本信息如下：姓名年齡工資zhang3181500li4181500wang5181600zhao6172000放入TreeSet排序后結(jié)果為：zhao6li4zhang3wang5importjava.util.HashSet;publicclassTest1{publicstaticvoidmain(String[]args){//TODOAuto-generatedmethodstubHashSet<Worker>hs=newHashSet<Worker>();Workerw1=newWorker("zhang3",18,1500);Workerw2=newWorker("lis4",18,1500);Workerw3=newWorker("wang5",18,1600);Workerw4=newWorker("zhao6",17,2000);hs.add(w1);hs.add(w2);hs.add(w3);hs.add(w4);System.out.println(hs.size());System.out.println(hs);}}classWorkerimplementsComparable<Worker>{Stringname;intage;doublesalary;publicWorker(){}publicWorker(Stringname,intage,doublesalary){=name;this.age=age;this.salary=salary;}@OverridepublicintcompareTo(Workero){//TODOAuto-generatedmethodstubif(this.age!=o.age){returnthis.age-o.age;}elseif(this.salary!=o.salary){//Integerinteger1=newInteger(this.salary)returnnewDouble(this.salary)pareTo(newDouble(o.salary));}elseif(.equals()){returnpareTo();}return0;}@OverridepublicinthashCode(){finalintprime=31;intresult=1;result=prime*result+age;result=prime*result+((name==null)?0:name.hashCode());longtemp;temp=Double.doubleToLongBits(salary);result=prime*result+(int)(temp^(temp>>>32));returnresult;}@Overridepublicbooleanequals(Objectobj){if(this==obj)returntrue;if(obj==null)returnfalse;if(getClass()!=obj.getClass())returnfalse;Workerother=(Worker)obj;if(age!=other.age)returnfalse;if(name==null){if(!=null)returnfalse;}elseif(!name.equals())returnfalse;if(Double.doubleToLongBits(salary)!=Double.doubleToLongBits(other.salary))returnfalse;returntrue;}@OverridepublicStringtoString(){//TODOAuto-generatedmethodstubreturnage+"/"+salary+"/"+name;}}10.〔Map〕關(guān)于以下Map接口中常見的方法put方法表示放入一個(gè)鍵值對(duì)，如果鍵已存在那么新值替換舊值，如果鍵不存在那么增加一個(gè)鍵值對(duì)。remove方法承受一個(gè)參數(shù)，表示從映射中移除其映射關(guān)系的鍵。get方法表示返回指定鍵所映射的值，get方法的參數(shù)表示移除的其映射關(guān)系的鍵，返回值表示與key關(guān)聯(lián)的值。要想獲得Map中所有的鍵，應(yīng)該使用方法ketSet，該方法返回值類型為Set集合。要想獲得Map中所有的值，應(yīng)該使用方法get，該方法返回值類型為指定鍵所映射的值。要想獲得Map中所有的鍵值對(duì)的集合，應(yīng)該使用方法entrySet，該方法返回一個(gè)Map.Entry類型所組成的Set。11.〔Map〕利用Map，完成下面的功能：從命令行讀入一個(gè)字符串，表示一個(gè)年份，輸出該年的世界杯冠軍是哪支球隊(duì)。如果該年沒有舉辦世界杯，那么輸出：沒有舉辦世界杯。附：世界杯冠軍以及對(duì)應(yīng)的奪冠年份，請(qǐng)參考本章附錄。publicclassBk18{publicstaticvoidmain(String[]args){//TODOAuto-generatedmethodstubBufferedReaderbr=newBufferedReader(newInputStreamReader(System.in));Stringyear=null;try{year=br.readLine();}catch(IOExceptione){//TODOAuto-generatedcatchblocke.printStackTrace();}Map<String,String>map=newHashMap<String,String>();map.put("2002","巴西");map.put("2006","意大利");map.put("2010","南非");if(map.containsKey(year)){System.out.println(map.get(year));}else{System.out.println("這一年沒有承辦世界杯！");}}}12.〔Map〕某學(xué)校的教學(xué)課程內(nèi)容安排如下：集合框架〔習(xí)題〕"o:button="t"target="_blank"href="://photo.blog.sina.cn/showpic.html#blogid=714a83710100ptie&url=:///orignal/714a8371t9dbaa80ef64e">集合框架〔習(xí)題〕"src="file:///C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\msohtmlclip1\01\clip_image002.png">完成以下要求：1〕使用一個(gè)Map，以教師的名字作為鍵，以教師教授的課程名作為值，表示上述課程安排。2〕增加了一位新教師Allen教JDBC3〕Lucy改為教CoreJava4〕遍歷Map，輸出所有的教師及教師教授的課程5〕*利用Map，輸出所有教JSP的教師。publicstaticvoidmain(String[]args){//TODOAuto-generatedmethodstubMap<String,String>map=newTreeMap<String,String>();map.put("Tom","CoreJava");map.put("John","Oracle");map.put("Susan","Oracle");map.put("Jerry","JDBC");map.put("Jim","Unix");map.put("Kevin","JSP");map.put("Lucy","JSP");System.out.println(map.size());map.put("Allen","JSP");System.out.println(map.size());map.remove("Lucy");map.put("Lucy","CoreJava");Set<String>set=map.keySet();for(Objectobj:set){System.out.println(map.get((String)obj));}for(Stringstr:set){if(map.get(str).equals("JSP")){System.out.println("教JSP的教師有："+str);}}}13.〔泛型〕使用泛型，改寫第5題packagelist;importjava.util.Iterator;importjava.util.LinkedList;publicclassTest2{publicstaticvoidmain(String[]args){//TODOAuto-generatedmethodstubLinkedList<Worker1>ll=newLinkedList<Worker1>();Worker1w1=newWorker1("zhang3",18,3000);Worker1w2=newWorker1("li4",25,3500);Worker1w3=newWorker1("wang5",22,3200);ll.add(w1);ll.add(w2);ll.add(w3);ll.add(1,newWorker1("zhao6",24,2200));ll.remove(w3);//用for循環(huán)遍歷for(inti=0;i<ll.size();i++){System.out.println(ll.get(i));}System.out.println("==================");//用迭代器遍歷Iteratoriterator=ll.iterator();while(iterator.hasNext()){System.out.println(iterator.next());}}}classWorker1{privateintage;privateStringname;privatedoublesalary;publicWorker1(){}publicWorker1(Stringname,intage,doublesalary){=name;this.age=age;this.salary=salary;}publicintgetAge(){returnage;}publicvoidsetAge(intage){this.age=age;}publicStringgetName(){returnname;}publicvoidsetName(Stringname){=name;}publicdoublegetSalary(){returnsalary;}publicvoidsetSalary(doublesalary){this.salary=salary;}publicvoidwork(){System.out.println(name+"work");}@OverridepublicinthashCode(){finalintprime=31;intresult=1;result=prime*result+age;returnresult;}@Overridepublicbooleanequals(Objectobj){if(this==obj)returntrue;if(obj==null)returnfalse;if(getClass()!=obj.getClass())returnfalse;Worker1other=(Worker1)obj;if(age!=other.age)returnfalse;returntrue;}@OverridepublicStringtoString(){//TODOAuto-generatedmethodstubreturnname+"/"+age+"/"+salary;}}14.〔泛型〕使用泛型和Map.Entry接口，改寫第12題的前4問15.*〔List〕寫出下面程序的輸出結(jié)果importjava.util.*;classMyClass{intvalue;publicMyClass(){}publicMyClass(intvalue){this.value=value;}publicStringtoString(){return“〞+value;}}publicclassTestList{publicstaticvoidmain(Stringargs[]){MyClassmc1=newMyClass(10);MyClassmc2=newMyClass(20);//實(shí)例化的對(duì)象實(shí)際上就是一個(gè)對(duì)象的地址，//list中保存的是對(duì)象的引用，因此mc4，mc1，和list下標(biāo)為1的對(duì)象都是指向的同一個(gè)對(duì)象MyClassmc3=newMyClass(30);Listlist=newArrayList();list.add(mc1);list.add(mc2);list.add(mc3);MyClassmc4=(MyClass)list.get(1)//這句話實(shí)際上就是把mc4指向了mc2對(duì)象的那個(gè)地址MyClassmc4=(MyClass)mc2;mc4.value=50;for(inti=0;i<list.size();i++){System.out.println(list.get(i));}}}16.*〔Set，HashSet，空指針〕有下面代碼importjava.util.*;classStudent{intage;Stringname;publicStudent(){}publicStudent(Stringname,intage){=name;this.age=age;}publicinthashCode(){returnname.hashCode()+age;}publicbooleanequals(Objecto){if(o==null)returnfalse;if(o==this)returntrue;if(o.getClass()!=this.getClass())returnfalse;Studentstu=(Student)o;if(.equals(name)&&stu.age==age)returntrue;elsereturnfalse;}}publicclassTestHashSet{publicstaticvoidmain(Stringargs[]){Setset=newHashSet();Studentstu1=newStudent();Studentstu2=newStudent(“Tom〞,18);Studentstu3=newStudent(“Tom〞,18);set.add(stu1);在添加stu1的時(shí)候會(huì)自動(dòng)調(diào)用hashcode和equals方法，而在這兩方法中，name的值為空，所以會(huì)出現(xiàn)空指針異常。set.add(stu2);set.add(stu3);System.out.println(set.size());}}以下說法正確的選項(xiàng)是：A.編譯錯(cuò)誤B.編譯正確，運(yùn)行時(shí)異常C.編譯運(yùn)行都正確，輸出結(jié)果為3D.編譯運(yùn)行都正確，輸出結(jié)果為217.*〔Set〕有如下兩個(gè)類〔只寫了類的屬性，請(qǐng)自行添加相應(yīng)的構(gòu)造方法和get/set方法〕集合框架〔習(xí)題〕"o:spid="_x0000_i1032"o:button="t"target="_blank"href="://photo.blog.sina.cn/showpic.html#blogid=714a83710100ptie&url=:///orignal/714a8371t9dbaa4c923c6">集合框架〔習(xí)題〕"src="file:///C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\msohtmlclip1\01\clip_image001.gif">要求，完善Worker和Address類，使得Worker對(duì)象能夠正確放入HashSet中：即將Worker放入HashSet中時(shí)不會(huì)出現(xiàn)重復(fù)元素。并編寫相應(yīng)測(cè)試代碼。18.*〔Map〕在原有世界杯Map的根基上，增加如下功能：讀入一支球隊(duì)的名字，輸出該球隊(duì)奪冠的年份列表。例如，讀入“巴西〞，應(yīng)當(dāng)輸出19581962197019942002讀入“荷蘭〞，應(yīng)當(dāng)輸出沒有獲得過世界杯19.*〔Map〕設(shè)計(jì)Account對(duì)象如下：集合框架〔習(xí)題〕"o:button="t"target="_blank"href="://photo.blog.sina.cn/showpic.html#blogid=714a83710100ptie&url=:///orignal/714a8371t9dba9df86404">集合框架〔習(xí)題〕"src="file:///C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\msohtmlclip1\01\clip_image001.gif">要求完善設(shè)計(jì)，使得該Account對(duì)象能夠自動(dòng)分配id。給定一個(gè)List如下：Listlist=newArrayList();list.add(newAccount(10.00,“1234〞));list.add(newAccount(15.00,“5678〞));list.add(newAccount(0,“1010〞));要求把List中的內(nèi)容放到一個(gè)Map中，該Map的鍵為id，值為相應(yīng)的Account對(duì)象。最后遍歷這個(gè)Map，打印所有Account對(duì)象的id和余額。importjava.util.ArrayList;importjava.util.HashMap;importjava.util.List;importjava.util.Map;importjava.util.Random;importjava.util.Set;publicclassBK20{publicstaticvoidmain(String[]args){Randomran=newRandom();System.out.println(ran.nextLong());Listlist=newArrayList();list.add(newAccount(10.00,"1234"));list.add(newAccount(15.00,"5678"));list.add(newAccount(0.0,"1010"));Mapmap=newHashMap();for(inti=0;i<list.size();i++){Accountaccount=(Account)list.get(i);map.put(account.getId(),account);}Set<Map.Entry<Long,Object>>set=map.entrySet();for(Map.Entry<Long,Object>obj:set){Accountacc=(Account)obj.getValue();System.out.println(obj.getKey()+"/"+acc.getBalance());}}}classAccount{privatelongid;privatedoublebalance;privateStringpassword;publicAccount(){}publicAccount(doublebalance,Stringpassword){this.id=newRandom().nextLong();this.balance=balance;this.password=password;}publiclonggetId(){returnid;}publicvoidsetId(longid){this.id=id;}publicdoublegetBalance(){returnbalance;}publicvoidsetBalance(doublebalance){this.balance=balance;}publicStringgetPassword(){returnpassword;}publicvoidsetPassword(Stringpassword){this.password=password;}}20.*〔List〕寫一個(gè)函數(shù)reverseList，該函數(shù)能夠承受一個(gè)List，然后把該List倒序排列。例如：Listlist=newArrayList();list.add(“Hello〞);list.add(“World〞);list.add(“Learn〞);//此時(shí)list為HelloWorldLearnreverseList(list);//調(diào)用reverseList方法之后，list為L(zhǎng)earnWorldHello21.**〔Map，Hash算法〕有如下代碼：importjava.util.*;classMyKey{intkeyValue;publicMyKey(){}publicMyKey(intvalue){this.keyValue=value;}}classMyValue{Stringvalue;publicMyValue(){}publicMyValue(Stringvalue){this.value=value;}publicStringtoString(){returnvalue;}}publicclassTestMap{publicstaticvoidmain(Stringargs[]){Mapmap=newHashMap();MyKeykey1=newMyKey(10);map.put(key1,newMyValue(“abc〞));map.put(newMyKey(10),newMyValue(“cde〞));System.out.println(map.get(key1));System.out.println(map.size());}}寫出該代碼的輸出結(jié)果。abc222.**〔Id，hashCode，equals〕為Worker類增加id屬性，用來唯一標(biāo)識(shí)一個(gè)員工。即：如果員工的id不同，那么不管其姓名、年齡、工資是否一樣，都認(rèn)為是不同的員工。局部代碼如下：classWorker{privatefinalLongid;privateStringname;privatedoublesalary;privateintage;//構(gòu)造方法…//get/set方法…publicbooleanequals(Objectobj){//1此處僅判斷id是否一樣if(this.id==obj.id){returntrue;}returnfalse;}publicinthashCode(){//2此處返回hashCode}}要求：1〕完善構(gòu)造方法和get/set方法。要求自動(dòng)分配Worker的id2〕完善equals方法。要求僅判斷id是否一樣3〕//2處，如果寫成return(int)(name.hashCode()+id.hashCode()+age+salary);是否正確為什么//這里對(duì)比的dquals方法任務(wù)只要id一樣就是同一個(gè)對(duì)象，23.**〔綜合〕有如下Student對(duì)象集合框架〔習(xí)題〕"o:button="t"target="_blank"href="://photo.blog.sina.cn/showpic.html#blogid=714a83710100ptie&url=:///orignal/714a8371t9dba99085eb8">集合框架〔習(xí)題〕"src="file:///C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\msohtmlclip1\01\clip_image001.gif">其中，classNum表示學(xué)生的班號(hào)，例如“class05〞。有如下ListListlist=newArrayList();list.add(newStudent(“Tom〞,18,100,“class05〞));list.add(newStudent(“Jerry〞,22,70,“class04〞));list.add(newStudent(“Owen〞,25,90,“class05〞));list.add(newStudent(“Jim〞,30,80,“class05〞));list.add(newStudent(“Steve〞,28,66,“class06〞));list.add(newStudent(“Kevin〞,24,100,“class04〞));在這個(gè)list的根基上，完成以下要求：1〕計(jì)算所有學(xué)生的平均年齡2〕計(jì)算各個(gè)班級(jí)的平均分packageset;importjava.util.ArrayList;importjava.util.HashMap;importjava.util.Iterator;importjava.util.List;importjava.util.Map;importjava.util.Set;publicclassBK24{publicstaticvoidmain(String[]args){//TODOAuto-generatedmethodstubList<Student>list=newArrayList<Student>();list.add(newStudent("Tom",18,100,"class05"));list.add(newStudent("Jerry",22,70,"class04"));list.add(newStudent("Owen",25,90,"class05"));list.add(newStudent("Jim",30,80,"class05"));list.add(newStudent("Steve",28,66,"class06"));list.add(newStudent("Kevin",24,100,"class04"));Mapmap=newHashMap();for(inti=0;i<list.size();i++){Studentstu=list.get(i);Stringstr=stu.getClassNum();if(map.containsKey(str)){Listl=(List)map.get(str);l.add(stu);}else{Listl=newArrayList();l.add(stu);map.put(str,l);}}Setset=map.keySet();Iteratoriterator=set.iterator();while(iterator.hasNext()){intsum=0;ObjectobjStu=iterator.next();Listl=(List)map.get(objStu);for(inti=0;i<l.size();i++){sum+=((Student)l.get(i)).getScore();}System.out.println(sum/l.size());}}}classStudent{privateStringname;privateintage;privateintscore;privateStringclassNum;publicStudent(Stringname,intage,intscore,StringclassNum){super();=name;this.age=age;this.score=score;this.classNum=classNum;}publicStringgetName(){returnname;}publicvoidsetName(Stringname){=name;}publicintgetAge(){returnage;}publicvoidsetAge(intage){this.age=age;}publicintgetScore(){returnscore;}publicvoidsetScore(intscore){this.score=score;}publicStringgetClassNum(){returnclassNum;}publicvoidsetClassNum(StringclassNum){this.c