我在从Java程序插入数据时遇到问题。我的问题是用户被问到“你想在Department Table中使用多少个元组？”
他们可以添加他们想要的许多元组。然后我问他们“你在学生桌上想要多少元组？”他们想要的却是多少。
好吧，我输入10表示学生表，有时候会跳过随机记录。有时我会得到1-8，或1,2,3,5,6,9或不同的变化。
我知道我的while循环是正确的，所以我不确定是什么导致这个，所以我希望有人可以查看我的代码并发现可能是我遗漏的东西。
/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package program2;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;
import java.util.Random;
public class Program2 {
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
// Variables
int instructornum=0;
int coursenum = 0;
int studentnum = 0;
int count = 0;
int departmentnum =0;
int counts= 0;
int minimum=0;
int x=0;
int teachesnum=0;
// Variables
//Connection to the database
Connection conn = null;
String url = "jdbc:mysql://localhost:3306/";
String dbName = "university1";
String Driver = "com.mysql.jdbc.Driver";
// Change the userName & password to what ever your credentials are.
String userName = "root";
String password = "121089bn";
//Connection to the database
try {
InputStreamReader istream = new InputStreamReader(System.in);
BufferedReader MyReader = new BufferedReader(istream);
Class.forName(Driver).newInstance();
conn = DriverManager.getConnection(url+dbName,userName,password);
System.out.println("Connected");
// Ask the user how many tuples in department table.
System.out.println("How many tuples would you like to create in Department Table?");
// Takes in as string the number then parse it to an int.
String dept = MyReader.readLine();
departmentnum = Integer.parseInt(dept);
// ****************** Department Table ******************//
while (count < departmentnum)
{
Statement st = conn.createStatement();
// Counts keeps the counter so the Primary Key is unique.
st.executeUpdate("Insert into department (dept_name, building, budget) values ('Dept "+counts+"', 'Voigt', '1200')");
count++;
counts++;
}
// ****************** Student Table ******************//
count=0;
counts=0;
System.out.println("How many tuples would you like to create in Student Table?");
String student = MyReader.readLine();
studentnum = Integer.parseInt(student);
while (count < studentnum)
{
Random ran = new Random();
int range = departmentnum - minimum + 1;
x = ran.nextInt(range) + minimum;
Statement st = conn.createStatement();
st.executeUpdate("Insert into student (id, name, dept_name,tot_cred) select '"+counts+"', 'Student "+counts+"', dept_name, '10' from department where dept_name='Dept "+x+"'");
count++;
counts++;
}
// ****************** Course Table ******************//
x=0;
count=0;
counts=0;
System.out.println("How many tuples would you like to create in Course Table?");
String course = MyReader.readLine();
coursenum = Integer.parseInt(course);
while (count < coursenum)
{
Random ran = new Random();
int range = departmentnum - minimum + 1;
x = ran.nextInt(range) + minimum;
Statement st = conn.createStatement();
st.executeUpdate("Insert into course (course_id, title, dept_name,credits) select '"+counts+"', 'Computer Science "+counts+"', dept_name, '3' from department where dept_name='Dept "+x+"'");
count++;
counts++;
}
// ****************** Instructor Table ******************//
x=0;
count=0;
counts=0;
System.out.println("How many tuples would you like to create in Instructor Table?");
String instructor = MyReader.readLine();
instructornum = Integer.parseInt(instructor);
while (count < instructornum)
{
Random ran = new Random();
int range = departmentnum - minimum + 1;
x = ran.nextInt(range) + minimum;
Statement st = conn.createStatement();
st.executeUpdate("Insert into instructor (id, name, dept_name,salary) select '"+counts+"', 'Instructor "+counts+"', dept_name, '10000' from department where dept_name='Dept "+x+"'");
count++;
counts++;
}
// ****************** Takes Table ******************//
x=0;
count=0;
counts=0;
System.out.println("How many tuples would you like to create in Teaches Table?");
String teaches = MyReader.readLine();
teachesnum = Integer.parseInt(teaches);
while (count < teachesnum)
{
Random ran = new Random();
int range = instructornum - minimum + 1;
x = ran.nextInt(range) + minimum;
Random random = new Random();
int courserange = coursenum - minimum + 1;
int y = random.nextInt(courserange) + minimum;
Statement st = conn.createStatement();
st.executeUpdate("Insert into teaches (id, course_id, semester, year) select id, course_id, 'Spring', '2010' from course, instructor where instructor.id='"+x+"' and course.course_id='"+y+"'");
count++;
counts++;
}
conn.close();
}
catch (Exception e) {
System.err.println("Error");
System.err.println(e.getMessage());
}
}
}
答案 0 :(得分：2)
您的问题可能是您正在为不存在的部门创建学生。你的范围变量等于departmentnum + 1，这意味着你nextInt()将返回0-departmentnum包含。
你是部门ID，但是，只从0到departmentnum - 1，因为你的while循环是count < departmentnum。要么让你的while循环为count <= departmentnum，要么摆脱你范围内的+ 1。
也欢迎来到stackoverflow：）
答案 1 :(得分：0)
我认为你遇到的问题是随机部门编号。假设用户输入5，您正在创建5个部门，其中Ids从0到4，而随机生成器选择0到5之间的数字。