1：先寫一個類，包括商品的基本屬性

package com.xt.java.base25;

public class Goods {

    private int ID;
    
    private String name;
    
    private int number;
    
    private double price;

    /**
     * @return the iD
     */
    public int getID() {
        return ID;
    }

    /**
     * @param iD the iD to set
     
 
*/
    public void setID(int iD) {
        ID = iD;
    }

    /**
     * @return the name
     */
    public String getName() {
        return name;
    }

    /**
     * @param name the name to set
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * @return the number
     
 
*/
    public int getNumber() {
        return number;
    }

    /**
     * @param number the number to set
     */
    public void setNumber(int number) {
        this.number = number;
    }

    /**
     * @return the price
     */
    public double getPrice() {
        return price;
    }

    /**
     * 
 
@param price the price to set
     */
    public void setPrice(double price) {
        this.price = price;
    }
    

    
    
}

2：將數據庫和Java連接起來，並寫成一個單獨的類，使用起來更加方便

package com.xt.java.base25;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class GoodDAO {
    
    private Connection conn;
    private Statement stat;
    private String  url="jdbc:mysql://localhost:3306/lyxdatabases";
    private String dbDriver="com.mysql.jdbc.Driver";
    private String userName="root";
    private String password="1234";
    //私有的構造方法，只有在本類中可以進行實例化一次，為了保護用戶的隱私使用這種方法，切記！！！
    private GoodDAO(){
        
    }
        
    private static GoodDAO gda=null;
    /**
     * 寫一個方法，從方法中獲得實例,只能實例化一次。
     */
    
    public static GoodDAO getGoodDAO(){
        if(gda==null){
            gda=new GoodDAO();
        }
        return gda;
    }
    
    public Connection getConnection() throws Exception{
          try {
            Class.forName(dbDriver);
            return DriverManager.getConnection(url,userName,password);
        } catch (ClassNotFoundException e) {
            throw new ClassNotFoundException("數據庫找不到驅動！！");
        } catch (SQLException e) {
            throw new SQLException("數據庫連接異常！！");
        }
    }
    
    //關閉Connection
    public void closeConnection(Connection conn){
        try{
            if(conn!=null){
                conn.close();
            }
            
        }catch(Exception e){
            System.out.println(e);
        }
    }

    
    //關閉Statement
    public void closeStatement(Statement stat){
        try{
            if(stat!=null){
                stat.close();
            }
            
        }catch(Exception e){
            System.out.println(e);
        }
    }
    //關閉ResultSet
    public void closeResultSet(ResultSet rs){
        try{
            if(rs!=null){
                rs.close();
            }
            
        }catch(Exception e){
            System.out.println(e);
        }
    }

    
    

}

3；主方法，直接實現功能

package com.xt.java.base25;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.Scanner;

public class Main {
    GoodDAO gDao=GoodDAO.getGoodDAO();
    Connection conn;
    Statement stat;
    ResultSet rs;
    Scanner scanner=new Scanner(System.in);
    static double sumMonNum;
    
    
    //顯示貨物清單， 清單要求包含每種商品的剩余數量。
    public void showList(){
        
        String sql="select *from autoGoods";
        try {
            conn=gDao.getConnection();
            stat=conn.createStatement();
            rs=stat.executeQuery(sql);
            while(rs.next()){
                System.out.println("商品編號："+rs.getString("ID"));
                System.out.print("商品名稱："+rs.getString("name"));
                System.out.print("  商品剩余數量："+rs.getInt("number"));
                System.out.print("商品單價："+rs.getDouble("price")+"\n\n");
                
            }
        } catch (Exception e) {
            e.printStackTrace();
        }finally{
            gDao.closeResultSet(rs);
            gDao.closeStatement(stat);
            gDao.closeConnection(conn);
        }
        
    }
    
    //選擇一個商品編號購買東西
    public void buyGoods(){
        System.out.println("請輸入你要購買的商品編號：");
        int buyID=scanner.nextInt();
        
        
        System.out.println("請投幣：");
        sumMonNum=scanner.nextDouble();
        
        System.out.println("您的商品將要出貨！！！");
        String sql="update autoGoods set number=(number-1) where ID=‘"+buyID+"‘";
        String sql1="select price from autoGoods where ID=‘"+buyID+"‘";
        
        
        try {
            conn=gDao.getConnection();
            stat=conn.createStatement();
            rs=stat.executeQuery(sql1);
            while(rs.next()){
                sumMonNum=sumMonNum-rs.getDouble("price");
                System.out.println("您的零錢為"+sumMonNum);
                
            }
            if(stat.executeUpdate(sql)>0){
                System.out.println("購買成功！！");
            }
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            gDao.closeResultSet(rs);
            gDao.closeStatement(stat);
            gDao.closeConnection(conn);
        }
    }
        //詢問繼續的操作
        public void askOpration(){
        while(true){
            System.out.println("--------請選擇您接下來得操作-------");
            System.out.println("繼續購買-------1");
            System.out.println("結束購買，找零-------2");
            int operationNum=scanner.nextInt();
            switch(operationNum){
            case 1:{
                System.out.println("請輸入你要購買的商品編號：");
                int buyID=scanner.nextInt();
                
                System.out.println("您的商品將要出貨！！！");
                String sql="update autoGoods set number=(number-1) where ID=‘"+buyID+"‘";
                String sql1="select price from autoGoods where ID=‘"+buyID+"‘";
            
                
                try {
                    conn=gDao.getConnection();
                    stat=conn.createStatement();
                    rs=stat.executeQuery(sql1);
                    while(rs.next()){
                        sumMonNum=sumMonNum-rs.getDouble("price");
                        if(sumMonNum<0){
                            System.out.println("余額不足，請重新選擇！！");
                            break ;
                        }else{
                        System.out.println("您的零錢為"+sumMonNum);
                        
                        if(stat.executeUpdate(sql)>0){
                            System.out.println("購買成功！！");
                            }    
                        } 
                    }
                }catch (Exception e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }finally{
                    gDao.closeStatement(stat);
                    gDao.closeConnection(conn);
                }
                break ;
            }
            
            case 2:{
                System.out.println("將要為您找零，謝謝您的使用，期待您的下次光臨~");
                System.exit(0);
                }
            }
        }
    }
    
    public static void main(String[] args) {
        Main main=new Main();
        while(true){
        main.showList();
        main.buyGoods();
        main.askOpration();
        
    }
    }
}

Java開發自動售貨機