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);
    }
}