疯狂java讲义 第八章课后题

1.创建一个Set集合，并用Set集合保存用户通过控制台输入的字符串。

 import java.util.HashSet;
 import java.util.Scanner;

 public class Homework1 {
     public static void main(String args[]) {
         HashSet<String> arrSet = new HashSet<String>();
         Scanner sc = new Scanner(System.in);
         while(sc.hasNextLine()) {
             String a = sc.nextLine();
             if(a.equals("")) {
                 break;
             }
             arrSet.add(a);
         }
         sc.close();
         System.out.println(arrSet);
     }
 }

2. 创建一个List集合，添加10个元素。然后获取索引为5处的元素；再获取其中某2个元素的索引；再删除索引为3处的元素。

 import java.util.ArrayList;

 public class Homework2 {
     public static void main(String args[]) {
         String[] books = {"语1","数2","英3","物4","化5","生6","政7","史8","地9","选10"} ;
         ArrayList<String> list = new ArrayList<String>();
         for (int i = 0; i < books.length; i++) {
             list.add(books[i]);
         }
         System.out.println(list);
         System.out.println(list.get(5));
         System.out.println(list.indexOf("数2"));
         System.out.println(list.indexOf("选10"));
         list.remove(3);
         System.out.println(list);
     }
 }

3. 给定字符串数组，然后使用Map的key来保存数组中字符串元素，value保存该字符串元素的出现次数，最后统计出各字符串元素的出现次数。

 import java.util.HashMap;

 public class Homework3 {
     public static int count(String[] str,String x) {
         int temp = 0;
         for (int i = 0; i < str.length; i++) {
             if (str[i] == x) {
                 temp++;
             }
         }
         return temp;
     }

     public static void main(String args[]) {
         String[] str = {"a","b","a","b","c","a","b","c","b"};
         HashMap<String, Integer> hm = new HashMap<String, Integer>();
         for (int i = 0; i < str.length; i++) {
             hm.put(str[i], 0);
         }
         System.out.println(hm);
         hm.put("a", count(str,"a"));
         hm.put("b", count(str,"b"));
         hm.put("c", count(str,"c"));
         System.out.println(hm);
     }
 }