這個班級設計是否錯誤？

Question

我開始作爲一個Java開發人員。我正在用java和mysql開發一個股票應用程序。

我有一個很大的問題。我無法想出我應該如何放置方法來保存數據。我應該爲數據庫操作創建一個新類，還是應該將它們放在庫存類中？

謝謝！

我的類別是：

package inventory; 

public class Item 
{ 
private String bc; // ITEM BARCODE 
private String description; // ITEM DESCRIPTION 
private int nItm; // NUMBER OF ITEMS IN A PACK OR ITEMS 

/** 
* Constructor for objects of class item 
* - Initialise instance variables bc, description to null and nItm to 0 
*/ 
public Item() 
{ 
    // initialise instance variables 
    bc = null; 
    description = null; 
    nItm = 0; 
} 

/** 
* Constructor for objects of class item 
* - Initialise instance variables to a given parameters. 
* @param bc   String item codebar. 
* @param description String description of the item. 
* @param nItm   int items or number of items in a pack 
*/ 
public Item(String bc,String description,int nItm) 
{ 
    this.bc = bc; 
    this.description = description; 
    this.nItm = nItm; 
} 

/** 
* Gets a codebar from the item 
* 
* @return  A String with the codebar item. 
*/ 
public String getBarcode() 
{ 
    // put your code here 
    return bc; 
} 

/** 
* Gets description from the item 
* 
* @return  A String with the description item. 
*/ 
public String getDescription() 
{ 
    return description; 
} 

/** 
* Gets the number of items in stock 
* 
* @return  Number of items in stock. 
*/ 
public int getNumberOfItems() 
{ 
    return nItm; 
} 

/** 
* Set the value for codebar 
* 
* @param bc Barcode item. 
*/ 
public void setBarcode(String bc) 
{ 
    this.bc = bc; 
} 

/** 
* Set the value for description 
* 
* @param description Description item. 
*/ 
public void setDescription(String description) 
{ 
    this.description = description; 
} 

/** 
* Set the value for nItm 
* 
* @param nItm Number of items or items in a pack 
*/ 
public void setNumberOfItems(int nItm) 
{ 
    this.nItm = nItm; 
} 
/** 
* Shows an item with this template "| %-16s | %-44s | %5d |" 
*/ 
public void showItem() 
{ 
    System.out.print("\f"); 
    System.out.printf("+------------------+----------------------------------------------+-------+\n"); 
    System.out.printf("| BARCODE   | DESCRIPTION         | STOCK |\n"); 
    System.out.printf("+------------------+----------------------------------------------+-------+\n"); 
    System.out.printf("| %-16s | %-44s | %5d |",this.bc,this.description,this.nItm); 
    System.out.printf("+-------------------------------------------------------------------------+\n"); 
} 

}

package inventory; 
import javax.swing.JTable; 
import javax.swing.table.DefaultTableModel; 
import DataBases.*; 
import java.util.Scanner; 
import java.sql.*; 
public class Inventory 
{ 
// instance variables - replace the example below with your own 
private Item[] inventory; // array of items 
public int nreg; // NUMBER OF ITEMS STORED 

/** 
* Constructor for objects of class Inventory 
*/ 
public Inventory() throws SQLException,ClassNotFoundException,InstantiationException,IllegalAccessException 
{ 
    // initialise instance variables 

    this.inventory = new Item[100]; 
    loadData(); 
} 

/** 
* An example of a method - replace this comment with your own 
* 
* @param y a sample parameter for a method 
* @return  the sum of x and y 
*/ 
public void addItem(String bc,String description,int nItm) 
{ 
    // put your code here 
    Item item; 
    item = new Item(bc,description,nItm); 
    inventory[nreg] = item; 
    nreg++; 
} 

/** 
* An example of a method - replace this comment with your own 
* 
* @param y a sample parameter for a method 
* @return  the sum of x and y 
*/ 
public void loadData() throws SQLException,ClassNotFoundException,InstantiationException,IllegalAccessException 
{ 
    Mysql c = new Mysql(); 
    ResultSet rs; 

    c.On(); 
    rs = c.ExeGet("SELECT * FROM item"); 
    while(rs.next()) 
    { 
     inventory[nreg] = new Item(rs.getString("barcode"),rs.getString("description"),rs.getInt("nItems")); 
     this.nreg++; 
    } 
    c.Off(); 
} 

/** 
* An example of a method - replace this comment with your own 
* 
* @param y a sample parameter for a method 
* @return  the sum of x and y 
*/ 
public void searchItem() 
{ 
    System.out.print("\f"); 
    int op; 
    System.out.printf("\tSEARCH MENU\n"); 
    System.out.printf("\t===========\n\n"); 
    System.out.printf("\t1.BY BARCODE.\n"); 
    System.out.printf("\t2.BY ITEM.\n"); 
    System.out.printf("\t3.BY NUMBER OF ITEMS.\n"); 
    System.out.printf("\t0.EXIT.\n\n"); 
    System.out.printf("\tOPTION: "); 

    Scanner reader = new Scanner(System.in); 
    op = reader.nextInt(); 
    switch(op) 
    { 
     case 0: break; 
     //case 1: searchByBarcode();break; 
     //case 2: searchByItem();break; 
     case 3: searchByNumberOfItems();break; 
     default: break; 
    } 
} 

/** 
* An example of a method - replace this comment with your own 
* 
* @param y a sample parameter for a method 
* @return  the sum of x and y 
*/ 
/* 
private void searchByBarcode() 
{ 
    int op; 
    int flag = 0; 
    Item reg = new Item(); 

    do{ 
     System.out.print("\f"); 
     System.out.println("OPTION 1. OK"); 
     System.out.printf("BARCODE: "); 
     String bc; 
     Scanner reader = new Scanner(System.in); 
     bc = reader.nextSt(); 
    // AQUI VA UN TRY COMO UNA CASA 
     for(int i=0;i<nreg;i++) 
     { 
      if (inventory[i].getBarcode() == bc) 
      { 
       reg = inventory[i]; 
       flag = 1; 
       break; 
      } 
     } 
     if (flag == 1) 
     { 
      reg.showItem(); 
     } 
     else 
     { 
      System.out.printf("I CAN NOT FIND %d",bc); 
     } 
     System.out.println("CONTINUE SEARCHING (0/1): "); 
     op = reader.nextInt(); 

    }while(op != 1); 
} 
*/ 

/** 
* An example of a method - replace this comment with your own 
* 
* @param y a sample parameter for a method 
* @return  the sum of x and y 
*/ 
private void searchByNumberOfItems() 
{ 
    System.out.print("\f"); 
    System.out.println("OPTION 3. OK"); 
} 

/** 
* An example of a method - replace this comment with your own 
* 
* @param y a sample parameter for a method 
* @return  the sum of x and y 
*/ 
public void addNewItem(String barcode,String description,int nItm) throws SQLException,ClassNotFoundException,InstantiationException,IllegalAccessException 
{ 
    Mysql c = new Mysql(); 
    Item i = new Item(barcode,description,nItm); 
    String q = "INSERT INTO inventory.item (barcode,description,nItems) VALUES ('" + i.getBarcode() + "','" 
       + i.getDescription() + "'," + i.getNumberOfItems() + ");"; 

    c.On(); 
    c.Exe(q); 
    c.Off(); 
    nreg++; 
} 

/** 
* An example of a method - replace this comment with your own 
* 
* @param y a sample parameter for a method 
* @return  the sum of x and y 
*/ 
public void listItems() throws SQLException,ClassNotFoundException,InstantiationException,IllegalAccessException 
{ 
    Mysql c = new Mysql(); 
    ResultSet rs; 

    c.On(); 
    rs = c.ExeGet("SELECT * FROM item"); 
    System.out.print("\f"); 
    System.out.printf("+------------------+----------------------------------------------+-------+\n"); 
    System.out.printf("| BARCODE   | DESCRIPTION         | STOCK |\n"); 
    System.out.printf("+------------------+----------------------------------------------+-------+\n"); 
    while(rs.next()) 
    { 
     //System.out.println("" + rs.getString("barcode") + "  " + rs.getString("description") + "  " + rs.getInt("nItems")); 

     System.out.printf("| %-16s | %-44s | %5d |\n",rs.getString("barcode"),rs.getString("description"),rs.getInt("nItems")); 
    } 
    System.out.printf("+-------------------------------------------------------------------------+\n"); 
    c.Off(); 
} 

public void listArray() 
{ 
    System.out.print("\f"); 
    System.out.printf("+------------------+----------------------------------------------+-------+\n"); 
    System.out.printf("| BARCODE   | DESCRIPTION         | STOCK |\n"); 
    System.out.printf("+------------------+----------------------------------------------+-------+\n"); 
    for(int i = 0;i<nreg;i++) 
    { 
     System.out.printf("| %-16s | %-44s | %5d |\n",inventory[i].getBarcode(),inventory[i].getDescription(),inventory[i].getNumberOfItems()); 
    } 
    System.out.printf("+-------------------------------------------------------------------------+\n"); 
    System.out.printf("| NUMBER OF ITEMS: %3d             |\n",nreg); 
    System.out.printf("+-------------------------------------------------------------------------+\n"); 
} 

}

package DataBases; 
import java.sql.*; 


public class Mysql 
{ 
// instance variables - replace the example below with your own 
private String host; 
private String user; 
private String pass; 
private String db; 
private int port; 
private Connection connection; 

/** 
* Constructor for objects of class Mysql 
*/ 
public Mysql()throws ClassNotFoundException,InstantiationException,IllegalAccessException 
{ 
    // initialise instance variables 
    this.host = "localhost"; 
    this.user = "inventory"; 
    this.pass = "123456"; 
    this.port = 3306; 
    this.db = "inventory"; 
    this.Init(); 
} 

public Mysql(String host,String user,String pass,int port,String db) throws ClassNotFoundException,InstantiationException,IllegalAccessException 
{ 
    this.host = host; 
    this.user = user; 
    this.pass = pass; 
    this.port = port; 
    this.db = db; 
    this.Init(); 
} 


public void Init() throws ClassNotFoundException,InstantiationException,IllegalAccessException 
{ 
    // put your code here 
    Class.forName("com.mysql.jdbc.Driver").newInstance(); 
} 

public void On() throws SQLException 
{ 

    this.connection = DriverManager.getConnection("jdbc:mysql://"+ this.host +"/" + this.db,this.user,this.pass); 
} 

public void Off() throws SQLException 
{ 

    this.connection.close(); 
} 

public ResultSet ExeGet(String Query) throws SQLException 
{ 
    Statement st = this.connection.createStatement(); 
    return (ResultSet) st.executeQuery(Query); 
} 

public int Exe(String Query) throws SQLException 
{ 

    Statement st = this.connection.createStatement(); 
    return st.executeUpdate(Query); 
} 

}

Answer 1

要快速回答是這是一個可怕的設計對不起，這裏是我會改善我t：

• 試着實現你的類之間的鬆耦合，每個類都應該是一個接口的實現。

  public interface ConnectionManager { 
      void On() throws SQLException; 
      void Off() throws SQLException; 
      ResultSet ExeGet(String Query) throws SQLException; 
      int Exe(String Query) throws SQLException; 
  } 
  
  public class MysqlConnectionManager implements ConnectionManager { 
      @Override 
      public void On() throws SQLException { 
      } 
      @Override 
      public void Off() throws SQLException { 
      } 
      @Override 
      public ResultSet ExeGet(String Query) throws SQLException { 
      } 
      @Override 
      public int Exe(String Query) throws SQLException { 
      } 
  } 
  

然後你的DAO將有一個這樣的引用（這可能注入）：

ConnectionManager connectionManager = new MysqlConnectionManager(); 

• 嘗試按照駱駝的情況下實踐（Wiki source）

• 您的屬性和關聯方法應根據您的屬性名稱共享相同的名稱。

  private String barCode; 
  
  public String getBarCode(){ 
      return this.barCode; 
  } 
  
  public void setBarCode(final String barCode){ 
      this.barCode = barCode; 
  } 
  

• 按照DAO模式（Wiki source），基本上你需要創建一個類名ItemDao會照顧所有操作與DB的「項目」。

• 該庫存應該重命名爲ItemService，並且它不應該訪問只有DAO纔會訪問的數據庫，所以如果您需要實現另一個DAO，則很容易將其替換。

• 不要過多地使用System.out.print，而是將您的類配置爲使用輸出流，因此可以使用文件或字符串輸出流輕鬆進行配置。

• 要注入數據到數據庫使用準備語句而不是你的查詢中串聯數據（SQL injection）