黑马面试相关-java技术总结集合练习

技术总结————集合第一题：创建两个List,先在其中一个存入若干 对象,然后将其中21岁的换到另publicclassExercise1publicstaticvoidmain(String[]{Listlist1=newArrayList(); ("", ("", ("", ("", ("",20));Listlist2=newArrayList();for(inti=0;i<list1.size(); p= )if(p.getAge()==21){}}}}.,的元素的位置,方法对两个索引上的元素进行交换.publicclassExercise2publicstaticvoidmain(String[]args){List<String>list=newArrayList<String>();list.add("a");swap(list,1,2);System.out.println(list);//a,c,b,}publicstaticvoidswap(Listlist,intindex1,intindex2)Objecttemp=list.get(index1); //记住1list.set(index1,list.get(index2));//获取2,把1替换为2list.set(index2,temp); //把2替换为记住的}}第三题：定义方法,List中的所有元素publicclassExercise3publicstaticvoidmain(String[]args){List<String>list=newArrayList<String>();list.add("a");reverse(list);//d,c,b,}publicstaticvoidreverse(ListListnewListnew for(inti=list.size()-1;i>=0;i--)//倒着遍历原List //将原List中所有元素添加到新List //清空原List //将新List}}第四题：定义方法,查找 publicclassExercise4publicstaticvoidmain(String[]args){List< list=newArrayList< >();list.add(new("", ("",23));} >oldest=list.get(0);//定义一 类型变量,用来记住最 ,最初记住第一for plist){//Listif(p.getAge()>oldest.getAge())//和变量记住的 比较,如果大于变量记住的oldest }return }},publicclassExercise5publicstaticvoidmain(String[]args){List<String>list=newArrayList<String>();list.add("a");System.out.println(countTimes(list,"a"));//3System.out.println(countTimes(list,"b"));//1System.out.println(countTimes(list,"c"));//2System.out.println(countTimes(list,"d"));//2}publicstaticintcountTimes(Listlist,Objectinttimes int变量,forObjectobjlist)//遍历if(obj.equals(key))key比较,times++;//如果相同变量+1returntimes; //循环结束后返回变量}}第六题：定义方法,用一个指定的对象替换集合中已存在的指定对象(替换所有的publicclassExercise6publicstaticvoidmain(String[]args){List<String>list=newArrayList<String>();Exercise6.replace(list,"b","o");System.out.println(list);// }publicstaticvoidreplace(Listlist,ObjectoldObj,Object{for(inti=0;i<list.size();i++)if(oldObj.equals(list.get(i)))list.set(i,}},publicclassExercise7publicstaticvoidmain(String[]args){List<String>list=newArrayList<String>();list.add("a");System.out.println(list);//a,b,c}publicstaticvoiddistinct(List{for(inti=0;i<list.size();for(intj=i+1;j<list.size();j++)if}}第八题：定义方法,List和多个相同类型的对象,publicclassExercise8publicstaticvoidmain(String[]args){List<String>list=newArrayList<String>();addAll(list,"a","b","c","c","d",addAll(list,"x","x","o",}publicstaticvoidaddAll(ListlistObjectarr类型...变量名"可变参数,可以for(Objectobj: //遍历数组,}},,publicclassExercise1publicstaticvoidmain(String[]args){List<String>list=newArrayList<String>();list.add("a");}publicstaticvoiddistinct(Listlist)SetsetnewLinkedHashSet();//Setset.addAll(list);//ListSetlist.clear();//清空List 将Set}},,publicclassExercise2publicstaticvoidmain(String[]args){List<String>list=newArrayList<String>();list.add("a");}publicstaticvoidsort(Listlist)Setset=newTreeSet(ne }} paratorimplements{publicintcompare(Stringo1,Stringo2){intgap= returngap!=0?gap:}}5个数字,5个数排序,publicclassExercise4publicstaticvoidmain(String[]args)throws{System.out.println("请输入5个数字:");BufferedReaderbrnewBufferedReader(new,for(inti=0;i<5;i++)Stringline= //键盘数intx=Integer.parseInt(line); //转为int //装入TreeSet排序} //}} paratorimplementsComparator<Integer为了改变默认顺序,定义publicintcompare(Integero1,Integer{intgap=o1-o2;returngap!=0?gap:1;}}3个学生的考试成绩对其按照总分排序,输出到屏幕.,70,70,80publicclassExercise5publicstaticvoidmain(String[]args)throws{BufferedReaderbrnewBufferedReader(newInputStreamReader(System.in));//BufferedReaderTreeSet<Student>set=newTreeSet<Student>(); 为了要排序,所以创建TreeSet集合forinti0i3;i //定义循环,3String[]arr= //数据,按逗号分Studentstu=newStudent(arr[0],Integer.parseInt(arr[1]),Integer.parseInt(arr[2]),Integer.parseInt(arr[3])); //每次将到的数据封装成一个对象,装到集合}for(Studentstu:System.out.println(stu);迭代TreeSet集合,}}publicclassExercise3publicstaticvoidmain(String[]args)throws{System.out.println("请输入一个字符串:");BufferedReaderbrnewBufferedReader(newStringline= //从键盘输入一行数据,再没敲回车之前符

chararr //HashSet<CharactersetnewHashSet<Character>();//定义集合,for(charc: //循环遍历数组,System.out.println("字符串line中包含set.size}}第十四题：统计一个字符串中每个字符出现的次数.例如:"abcbcd"a=1,b=2,c=2,x=3,d=1publicclassExercise1publicstaticvoidmain(String[]{Strings="abcmethod1(s);//没有顺序:{d=1,b=2,c=2,a=1,x=3}method2(s);//字母顺序:{a=1,b=2,c=2,d=1,x=3}method3(s);//出现顺序:{a=1,b=2,c=2,x=3,d=1}method4(s);//次数顺序:{a=1,d=1,b=2,c=2,x=3}}privatestaticvoidmethod4(Strings)Map<Character,Integer>map=new

for(charc:map.put(c,map.containsKey(c)?map.get(c)+1://获取Map中的所有Entry(一个键和一个值组成的对象)Set<Entry<Character,Integer>>entrySet=m //Entry排序,创建一个Set<Entry<Character,Integer>>sortSet=newTreeSet<Entry<Character, 将MapEntryTreeSetValue//}privatestaticvoidmethod3(Strings)Map<Character,Integer>map=new}

for(charc:map.put(c,map.containsKey(c)?map.get(c)+1:1);privatestaticvoidmethod2(Strings)Map<Character,Integer>map=newTreeMap<Character,Integer>();for(charc:s.toCharArray())map.put(c,map.containsKey(c)?map.get(c)+1:1);}privatestaticvoidmethod1(Strings)char[]arr=s.toCharArray(); //转换为char[]Map<CharacterInteg