Java MySQL 与 ArrayLists 的集成 [英] Java MySQL integration with ArrayLists

问题描述

我试图让我的程序能够运行多次.这意味着如果我在我的程序中输入一些东西然后关闭它，当我启动它时，在 MySQL 的帮助下，该信息仍然存在.我对 Java 和 MySQL 还很陌生，但这非常重要.我的程序运行良好，但我不知道如何让 MySQL 保存数组列表.我已经建立了包含我需要的一切的数据库.到目前为止，这是我的 MySQL 桥:

I am trying to get my program to be able to run over multiple runs. Meaning if I input something in my program and then shut it down, when I start it back up that info will still be there with the help of MySQL. I am fairly new to Java and MySQL but this is very important. My program works perfectly but I have no idea how to get MySQL to hold the arraylist. I already have the database set up with everything I need. This is my MySQL bridge so far:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
public class SQL {
    Class.forName("com.mysql.jdbc.Driver");
    Connection con = DriverManager.getConnection("jdbc:mysql://instance23389.db.xeround.com:15296/Inventory","user","password");
    PreparedStatement Statement = con.prepareStatement("Select * from name");
    ResultSet result = Statement.executeQuery();
    {
        while(result.next())
        {

        }
    }
}

还有这一行:

    Class.forName("com.mysql.jdbc.Driver");
throws "Syntax error on token ""com.mysql.jdbc.Driver"", delete this token"

而且我已经为桥导入了正确的文件.

and I have already imported the correct files for the bridge.

我也尝试了以下代码.它运行时没有错误，但它不会从数据库中导入信息.我从那里去哪里?

I also tried the following code. It runs with no errors but it isn't importing the info from the database. Where do I go from there?

public static void main(String[] args) throws SQLException
    {
         Connection con = DriverManager.getConnection("jdbc:mysql://instance23389.db.xeround.com:15296/Inventory","user","password");
        PreparedStatement Statement = con.prepareStatement("Select * from inventory");
        ResultSet result = Statement.executeQuery();
        while(result.next()) {
            // do something with the row
        }



    @SuppressWarnings("resource")
    Scanner input = new Scanner(System.in);
    int x=0;
    int choice;
    do{
        do
        {
            System.out.println("Please select what you would like to do:\n1 = Add New\n2 = Update Inventory\n3 = Lookup Inventory\n4 = Make Changes\n5 = Totals");
            choice=input.nextInt();
            if(choice<1 || choice>5)
            {
                System.out.println("Please enter a number 1-5.");
            }
            else
            {

            }
        }while(choice<1 || choice>5);
        if(choice==1)
        {
            Product_Chart.newInv();
        }
        else if(choice==2)
        {
            Product_Chart.updateInv();
        }
        else if(choice==3)
        {

            Product_Chart.lookupInv();
        }
        else if(choice==4)
        {
            Product_Chart.MakeChanges();
        }
        else if(choice==5)
        {
            Product_Chart.Totals();// TODO does not call Product_Chart.Totals();
        }
        else
        {
            System.out.println("Error 101");
        }
    }while(x==0);
}
}

推荐答案

本声明:

Class.forName("com.mysql.jdbc.Driver");

位于类的顶层 - 您通常会在其中拥有变量声明、方法或构造函数.你可能想把它放在一个静态初始化器中:

is at the top level of the class - where you'd normally have variable declarations, methods, or constructors. You might want to put it in a static initializer:

static {
    Class.forName(...);
}

...虽然我认为这一步已经有一段时间没有必要了.(基本上，驱动程序发现过程得到了改进.)

... although I thought that this step had been unnecessary for quite some time. (The driver discovery process has improved, basically.)

至于让 MySQL 持有 ArrayList" - 您需要插入、更新或删除数据库的内容以匹配您的数据.这是一个过于广泛的主题，无法在一个答案中涵盖，但您应该阅读有关如何修改数据以及仅选择数据的教程.

As for getting MySQL to "hold the ArrayList" - you need to insert, update or delete the contents of the database to match your data. It's too broad a topic to cover in a single answer, but you should read tutorials about how to modify data as well as just selecting it.

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