大数据双元基础班-day11集合

12天集合SetHashSet第1Set集合特点和HashSetSet一个不包含重复元素的collection它不保证set案例代码一packagepackageimportjava.util.HashSet;importjava.util.Set;一个不包含重复元素的它不保证set的迭代顺序；特别是它不保证该顺序恒久不publicpublicclassSetDemopublicstaticvoidmain(String[]args)Set<String>set=newfor(Strings:set){}}}HashSet它不保证setHashSetHashSet通过查看add方法的源码，知道了添加功能的执行过程中，是进行了首先比较对象的哈希值是否相同，这个哈希值是根据对象的hashCode如果哈希值相同，继续执行equals()进行比较，返回的是true，说明元素重复，不添加。返回的是false，说明元素不重复，就添加。如果使用HashSet集合对象，你要想保证元素的唯一性，就必须重写hashCode()和equals()方法。案例代码二packagepackageimport*通过查看add方法的源码 *******如首先比较对象的哈希值是否相同，这个哈希值是根据对象的hashCode()如果哈希值相同，继续执行equals()进行比较，返回的是true，说明元素重复，不添加。返回的是false使用HashSet集 publicclassHashSetDemopublicstaticvoidmain(String[]args)HashSet<String>hs=new for(Strings:hs){}}}HashSet集合的练习自定义对象并遍HashSet集合自定义对象并遍name和age增强for案例代码三packagepackagepublicclassStudent{privateStringname;privateintage;publicStudent()}publicStudent(Stringname,intage)=this.age=}}publicStringgetName()return}publicvoidsetName(Stringname)=}publicintgetAge()return}publicvoidsetAge(intage)this.age=}}案例代码四packagepackageimportimportHashSet集 增强publicclassHashSetTestpublicstaticvoidmain(String[]args)HashSet<Student>hs=newStudents1=newStudent("Students2=newStudentStudents3=newIterator<Student>it=hs.iterator();Students=it.next();} //增强for(Students:hs){}}}HashSet集合的练习自定义对象保证元素唯一HashSet集合自定义对象并遍name和age增强for因为的元素所属的类没有重写hashCode()和equals()方法所以案例代码五packagepackagepublicclassStudent{privateStringname;privateintage;publicStudent()}publicStudent(Stringname,intage)=this.age=}publicStringgetName()return}publicvoidsetName(Stringname)=}publicintgetAge()return}publicvoidsetAge(intage)this.age=}publicinthashCode()finalfinalintprime=intresult=result=prime*result+result=prime*result+((name==null)?0:return}publicbooleanequals(Objectobj)if(this==returntrue;if(obj==returnif(getClass()!=returnStudentother=(Student)if(age!=returnfalse;if(name==null){if(!=null)returnfalse;}elseifreturnfalse;returntrue;}}案例代码六packagepackageimportHashSet集 增强**而的元素所属的类没有重写hashCode()和equals()publicclassHashSetTestpublicstaticvoidmain(String[]args)HashSet<Student>hs=newStudents1=newStudent("Students2=newStudent("Students3=newStudent("Students4=newStudents5=new//增强for(Students:hs){}}}第2MapMap publicinterface案例代码六packagepackageimportimport***将 * *****publicinterface*publicclassMapDemopublicstaticvoidmain(String[]args)Map<String,String>map=new//put(Kkey,Vvalue):添加元素。map.put("it001"," map.put("it002", map.put("it003", }}MapVput(Kkey,VvalueVremove(Objectkey):根据键删除键值对元素voidclear():移除所有的键值对元素booleancontainsKey(Objectkey)：判断集合是否包含指定的键booleancontainsValue(Objectvalue):判断集合是否包含指定的值booleanisEmpty()：判断集合是否为空intsize案例代码七packagepackageimportimportVput(Kkey,Vvalue):Vremove(Objectkey):voidclear():booleancontainsKey(Objectkey)booleancontainsValue(Objectvalue):booleanisEmpty()：判断集合是否为intsize()publicclassMapDemo2publicstaticvoidmain(String[]args)Map<String,String>map=new//Vput(Kkey,Vvalue): 元素，返回 ", "," "," ", "," //Vremove(Objectkey): //voidclear()://booleancontainsKey(Objectkey)：判断集合是否包含指定的 //booleancontainsValue(Objectvalue):判断集合是否包含指定的值练//boolean//booleanisEmpty()//intsize()：返回集合中的键值对的对数}}MapVget(Objectkey):根据键获取值Set<K>keySet():获取所有键的集合Collection<V>values(案例代码八packagepackageimportjava.util.Collection;importjava.util.HashMap;importjava.util.Map;importVget(Objectkey):根据键获取Set<K>keySet():获取所有键的集Collection<Vvalues():publicclassMapDemo3publicstaticvoidmain(String[]args)Map<String,String>map=new", ", //Vget(Objectkey): //Set<KkeySet():Set<String>set=map.keySet();for(Stringkey:set){} Collection<String>values=map.values();for(Stringvalue:values){}}}MapMap思路：Map案例代码九packagepackageimportjava.util.HashMap;importjava.util.Map;importMap*********publicclassMapDemopublicstaticvoidmain(String[]args)Map<String,String>map=new Set<String>set=for(Stringkey:set){Stringvalue=map.get(key);}}}Map案例代码十packagepackageimportimportjava.util.Map;importMap*********publicclassMapDemo2publicpublicstaticvoidmain(String[]args)Map<String,String>map=new ntry<K,V>> ntry<String,String>>set= ntry<String,String>me:set){Stringkeyme.getKey();Stringvalue=me.getValue();}}}Map第3HashMapHashMapString键：String学号值：Student学生对象案例代码十一packagepackagepublicclassStudent{privateStringname;privateintage;publicStudent()}publicStudent(Stringname,intage)=this.age=}publicStringgetName()return}publicvoidsetName(Stringname)=}publicintgetAge()return}publicpublicvoidsetAge(intage)this.age=}}案例代码十二packagepackageimportimportjava.util.Map;import 键：String学值：StudentpublicclassHashMapTestpublicstaticvoidmain(String[]args)创建集合对HashMap<String,Student>hm=newHashMap<String,创建元素对Students1=newStudent("Students2=newStudents3=new",",",添加元素到集合hm.put("it001",hm.put("it002",hm.put("it003",遍Set<String>set=hm.keySet();for(Stringkey:set){Studentvalue=System.out.println(key+"---"+value.getName()+"---"} ntry<String,Student>>set2=hm.entrySet();for(M ntry<String,Student>me:set2){Stringkey=me.getKey();Studentvalue=me.getValue();System.out.println(key+"---"+value.getName()+"---"+}}}HashMapStudent练习2：任选式遍历键：Student学生对象值：String学生住址案例代码十三packagepackagepublicclassStudent{privateStringname;privateintage;publicStudent()}publicStudent(Stringname,intage)=this.age=}publicStringgetName()return}publicvoidsetName(Stringname)=}publicintgetAge()return}publicvoidsetAge(intage)this.age=}publicinthashCode(){finalintprime=31;intresult=1;result=prime*result+result=prime*result+((name==null)?0:return}publicbooleanequals(Objectobj)if(this==returntrue;if(obj==returnif(getClass()!=returnStudentother=(Student)if(age!=returnfalse;if(name==null){if(!=null)returnfalse;}elseifreturnfalse;returntrue;}}}案例代码十四packagepackageimportimport*练习2键：Student值：String学生住publicclassHashMapTestpublicstaticvoidmain(String[]args)HashMap<Student,String>hm=newStudents1=newStudent("Students2=newStudent("Students3=newStudent("Students4=newhm.put(s1, hm.put(s2, hm.put(s3西安hm.put(s4, Set<Student>set=hm.keySet();for(Studentkey:set){Stringvalue=}}}}ArrayList嵌套需求：ArrayList集合嵌套HashMap定义一个ArrayList集合，它包含三个元素，每一个元素都是每一个HashMap集合的键和值都是String类型的， 值 妻子第一个HashMap集合的元素：第二个HashMap小第三个HashMap案例代码十五packagepackageimportimportjava.util.HashMap;importjava.util.Set;需求：ArrayList集合嵌套HashMap集合并遍历定义一个ArrayList集合，它包含三个元素，每一个元素都是HashMap类型的每一个HashMap集合的键和值都是String键 值 第一个HashMap集合的元素第二个HashMap集合的元素小第三个HashMap集合的元素publicclassArrayListIncludeHashMapTest{publicstaticvoidmain(String[]args){ //创建元素HashMap<String,String>hm1=newHashMap<String,String>(); //把元素添加到array//创建元素HashMap<String,String>hm2=newHashMap<String,String>(); //把元素添加到array//创建元素HashMap<String,String>hm3=newHashMap<String,String>(); ////把元素添加到array//遍历ArrayListfor(HashMap<String,String>hm:array){Set<String>set=hm.keySet();for(Stringkey:set){Stringvalue=hm.get(key);} }}}HashMap嵌套需求：HashMap集合嵌套ArrayList定义