作业

 

Day01_统计字符串中重复字符出现个数 (集合联系map)

package com_01_testfan_02_basic;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

public class Day01_06_作业 {

	public static void main(String[] args) {
		// TODO 自动生成的方法存根
		/*
		 *需求：1.统计字符串中重复单词出现个数 (集合联系map)
		 *    2.数据demo如22dddddscvllljkkldfff
		 */
		
		String str_processedString = "22dddddscvllljkkldfff";
		Map<Character, Integer> map = new HashMap<Character, Integer>();
		//将字符放入临时字典中
		char[] ar = str_processedString.toCharArray();
		for (char c : ar) {
			//System.out.println(c);
			if (!map.containsKey(c)) {
				map.put(c, 1);
			} else {
				map.put(c, map.get(c)+1);
			}
		}
		//从临时字典中将数据取出来
		Set<Character> set = map.keySet();
		for (Character character : set) {
			System.out.println(character + " " + map.get(character));
		}
		
	}

}

　

老师代码

TreeMap 进行排序

LinkedHashMap 先进先出

HashMap 无序

package com_01_testfan_02_basic;

import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

public class Day01_06_作业2 {
    
    
    public static void main(String[] args) {
        String testString="2342a2sfghgyu56asdasdaddddd";
        //0 //length()-1
        //char char_str =testString.charAt(testString.length()-1);
        //Map<String, Integer> mapcount = new LinkedHashMap<String, Integer>();
        //Map<String, Integer> mapcount = new TreeMap<String, Integer>();
        Map<String, Integer> mapcount = new HashMap<String, Integer>();
        
        for (int i = 0; i < testString.length(); i++) {
            //System.out.println(testString.charAt(i));
            String key =String.valueOf(testString.charAt(i));
            //如果map 不存在 value 1
            if(!mapcount.containsKey(key)) {
                mapcount.put(key, 1);
            }else {
            //如果存在
                int value = mapcount.get(key);
                value +=1;
                mapcount.put(key, value);
            }
        }
        
        Set<String> keySet =mapcount.keySet();
        for (String key : keySet) {
            System.out.println(key +" "+mapcount.get(key));
        }
        
        //System.out.println(char_str);
    }

}

 

Day02_数据存放在硬盘中

将数据库获取的数据存放在硬盘中

package com.testfan.db;

//数据库模拟对象 
public class DbUser {
    private String uid;
    private String loginname;
    private String loginpass;
    public String getUid() {
        return uid;
    }
    public void setUid(String uid) {
        this.uid = uid;
    }
    public String getLoginname() {
        return loginname;
    }
    public void setLoginname(String loginname) {
        this.loginname = loginname;
    }
    public String getLoginpass() {
        return loginpass;
    }
    public void setLoginpass(String loginpass) {
        this.loginpass = loginpass;
    }
    @Override
    public String toString() {
        //return "DbUser [uid=" + uid + ", loginname=" + loginname + ", loginpass=" + loginpass + "]";
        return "";
    }

}

package com.testfan.db;

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

public class DbTest {
    
    public static void main(String[] args) throws Exception {
        String path = "D:\\user.csv";
        List<DbUser> list = getAllDbUserTest();
        //System.out.println(list.size());
        for (DbUser dbUser : list) {
            String nameString = dbUser.getLoginname();
            String uid = dbUser.getUid();
            String pass = dbUser.getLoginpass();
            String resultLine = nameString +","+ uid +","+ pass;
            writeToFile(resultLine, path);
            //System.out.println(resultLine);
        }
        //String line = "abdd";
    

    }


    //jdk 原始代码
    public static List<DbUser> getAllDbUserTest(){
        Connection conn = null;
        Statement statement = null;
        List<DbUser> list =null;
        try {
            //找一个工具去连接数据库
            Class.forName("com.mysql.cj.jdbc.Driver");
            //连接数据库
            conn = DriverManager.getConnection
            ("jdbc:mysql://118.24.13.38:3308/test?characterEncoding=utf8&useSSL=false", "zhangsan", "123123");
            
            //准备sql
            String  sql= "select * from t_user_test";
            
            //创建执行sql对象
            statement = conn.createStatement();
            //执行sql, 获取返回结果集合
            ResultSet  set=statement.executeQuery(sql);
            list = new ArrayList<DbUser>();
            while (set.next()) {
                DbUser user = new DbUser();
                user.setUid(set.getString("uid"));
                user.setLoginname(set.getString("loginname"));
                user.setLoginpass(set.getString("loginpass"));
                list.add(user);
                //System.out.println(set.getString("uid")+" "+set.getString("loginname")+" "+set.getString("loginpass"));
            }
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            //数据库关闭
            try {
                conn.close();
                statement.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        return list;
    }

    
    
    /**
     *  功能：将数据追加写入文本文件中
     * @param line
     * @throws IOException
     */
    private static void writeToFile(String line, String path) throws IOException {
        BufferedWriter br= new BufferedWriter(new FileWriter(path, true));
        br.write(line);
        br.newLine();
        br.close();
    }
    
}

老师代码如下