Java连接oracle数据库以及Java里HashMap的使用

使用eclipse连接oracle12c数据库，并完成了一些简单的操作（HashMap的使用）

任务：计算每位老师的工作量（Java编程）
计算方法是：讲授的每门课程的学时数*该门课程选修的学生人数，然后求和;

首先需要导入一个包，参考了以下这个博客

https://blog.youkuaiyun.com/hyh17808770899/article/details/106872076

以下是三个表，分别为课程表，课程安排表和学生选课表，

import java.sql.*;
import java.util.HashMap;
import java.util.Iterator;

import com.sun.javafx.collections.MappingChange.Map;

public class test {
	public static void main(String args[]) throws ClassNotFoundException, SQLException {
		//1.加载驱动
		Class.forName("oracle.jdbc.driver.OracleDriver");
		//2.获取连接对象
		String url = "jdbc:oracle:thin:@localhost:1521:orcl";
		String user = "***";   // 此处为自己的oracle用户名
		String password="123456";  // 这里为用户名所对应的密码

		Connection connection = DriverManager.getConnection(url,user,password);
		if(connection==null) {
			System.out.println("oracle失败");
		}else {
			System.out.println("oracle连接成功");
		}				
		/*String sql = "select sno,sum(grade) sg from sc group by sno";
			 try{
			   Statement statement = connection.createStatement();
			   ResultSet resultSet = statement.executeQuery(sql);
			   while (resultSet.next()){
			         String sno =resultSet.getString("sno");
			         double sg = resultSet.getDouble("sg");
			         System.out.println(sno);
			         System.out.println(sg);
			    }
		}catch(SQLException e){
		 e.printStackTrace();
		}*/
		
		// 统计出选修了每一门课程的 学生数*每一门的课时数，并将其存储在map_1中
		String sql_1 = "select cno, count(*) num from sc group by cno";				
		String sql_2 = "select cno, class_hour from course";
		
		HashMap<String, Double> map_1 = new HashMap<String, Double>();
		
		try{
			   Statement statement_1 = connection.createStatement();			  
			   ResultSet resultSet_1 = statement_1.executeQuery(sql_1);			   			   
			   
			   while (resultSet_1.next()){
			         String cno_1 = resultSet_1.getString("cno");
			         double num = resultSet_1.getDouble("num");	
			         
			         Statement statement_2 = connection.createStatement();			  
					 ResultSet resultSet_2 = statement_2.executeQuery(sql_2);
					 
			         while(resultSet_2.next()){
			        	 double workload;
			        	 String cno_2 = resultSet_2.getString("cno");
			        	 double class_hour = resultSet_2.getDouble("class_hour");
			        	 
			        	 if(cno_1.equals(cno_2)){			        		
			        		 workload = num*class_hour;
			        		 map_1.put(cno_2, workload);
			        		 System.out.println("课程号为"+cno_2+"的总学时为："+workload);
			        		 break;
			        	 }
			         }			         
			   }
			}
		 catch(SQLException e){
		    e.printStackTrace();
		 }				

		// 统计每一个教师的工作量,并将其存入map_2
		String sql_3 = "select tno, cno from tc";
		Statement statement_3 = connection.createStatement();			  
		ResultSet resultSet_3 = statement_3.executeQuery(sql_3);	
		HashMap<String, Double> map_2 = new HashMap<String, Double>();
		
		while(resultSet_3.next()){
			String tno = resultSet_3.getString("tno");
			String cno = resultSet_3.getString("cno");
			double class_hours = map_1.get(cno);
			if(!map_2.containsKey(tno))
				map_2.put(tno, class_hours);
			else
				map_2.put(tno, map_2.get(tno)+class_hours);		
		}
		
		// 遍历整个map_2将教师的工作量输出出来
		for(HashMap.Entry<String, Double> entry : map_2.entrySet()){
		    String mapKey = entry.getKey();
		    double mapValue = entry.getValue();
		    System.out.println("工号为"+mapKey+"的教师的工作量为："+mapValue+"学时");
		}				   
	}
}

结果：