java - 如何将同一个对象的不同实例添加到Java中的LinkedList中？

Question

我在这里设计一个商店系统，它主要是一个媒体商店，包含视频游戏、DVD和CD等元素。我遇到的问题是我想将同一对象(在本例中为视频游戏)的不同实例存储到链接列表中。它似乎有效，但是当我输出列表时，它只输出输入到列表中的最后一个项目，并重复自身以获取列表中应该包含的对象数量。

我知道需要查看大量代码，但我们将非常感谢任何帮助。

以下是 addVideoGame 类的代码:

import java.util.*;
import java.io.*;

public class addVideoGame extends VideoGames implements java.io.Serializable{

public static VideoGames game = new VideoGames();
public static VideoGames eGame = new VideoGames();
public static LinkedList <VideoGames> games = new LinkedList<>();
private static int vgChoice = 0;
public static int vgCount = 0;
public static int vgAmount = 0;

public static void vgMenu(){
    IBIO.output("1: Add a new videogame to the list.");
    IBIO.output("2: View the contents of the list.");
    IBIO.output("3: Save the contents of the list to the local area.");
    IBIO.output("4: Load in data from a local file.");
    IBIO.output("5: Return to the main menu.");
    vgChoice = IBIO.inputInt("Make your choice: ");

    if(vgChoice == 1){
        vgAmount = IBIO.inputInt("How many games would you like to add to the database?: ");
        for(int x = 0; x < vgAmount; x = x + 1){
        VideoGames vg = new VideoGames(); 
        vg.setTitle(IBIO.inputString("Enter the title of the game: "));
        vg.setPublisher(IBIO.inputString("Enter the publisher of the game: "));
        vg.setDeveloper(IBIO.inputString("Enter the developer of the game: "));
        vg.setAgeRating(IBIO.inputInt("Enter the age rating of the game: "));
        vg.setGenre(IBIO.inputString("Enter the genre of the game: "));
        vg.setQuantity(IBIO.inputInt("Enter the available quantity of the game: "));
        game = vg;
        games.add(vg);
        IBIO.output(" ");
        }
        vgMenu();
    } else if(vgChoice == 2){
        IBIO.output("Current amount of games in the list: " + games.size());
            System.out.println(Arrays.toString(games.toArray()));
        vgMenu();
    } else if(vgChoice == 3){
        try{
            FileOutputStream fileOut = new FileOutputStream("I:\\IB\\Computer Science\\TheStore\\games.txt");
            ObjectOutputStream out = new ObjectOutputStream(fileOut);
            out.writeObject(game);
            out.close();
            fileOut.close();
            IBIO.output("Data has been saved to: I:\\IB\\Computer Science\\TheStore\\games.txt");
            vgMenu();
        } catch(IOException i){
            i.printStackTrace();
        }
    } else if(vgChoice == 4){
        eGame = null;
        for(int x = 0; x < games.size(); x = x + 1){
        try{
            FileInputStream fileIn = new FileInputStream("I:\\IB\\Computer Science\\TheStore\\games.txt");
            ObjectInputStream in =  new ObjectInputStream(fileIn);
            eGame = (VideoGames) in.readObject();
            in.close();
            fileIn.close();
        } catch (IOException i){
            i.printStackTrace();
            return;
        } catch(ClassNotFoundException c){
            IBIO.output("VideoGames class not found");
            c.printStackTrace();;
            return;
        }
        IBIO.output("Object Details: " + eGame.toString());
        vgMenu();
        }
    } else if(vgChoice == 5){
        IBIO.output("Returning to main menu: ");
        AccessMenus.adminMenu();
    } 
}     

}

如果有人需要它们，这里是用于导航程序的两个接口(interface)类:

public class TheStore {

static String password; //Variable created to hold and check the value of password against the correct value.
public static boolean privilege = false; //Variable created to distinguish the difference between a normal user and a user with administrator privileges.

public static void main(String[] args) {
    IBIO.output("Welcome to The Store!");
    IBIO.output("Please make sure that you enter the correct password for your given privileges.");
    password = IBIO.inputString("Enter password: ");
    if(password.equalsIgnoreCase("admin")){ //Checks the entered value against the correct value.
        privilege = true; //Sets global boolean value to true, so that admin access is granted.
        IBIO.output(" ");
        AccessMenus.adminMenu();//If password is correct, loads admin menu.
    } else if(password.equalsIgnoreCase("user")){
        privilege = false; //Keeps admin access off, so that unauthorised changes cannot be made.
        IBIO.output(" ");
        AccessMenus.userMenu();//If correct, loads user menu.
    } else {
        IBIO.output("The password is incorrect. Exiting program."); 
        System.exit(1); //If an incorrect password is entered, the program will close.
    } //close else
}//close main
}//close class TheStore

第二个:

public class AccessMenus{

    public static int choice;//Variable which will hold the value, which corresponds to an action depending on what value is entered.

    public AccessMenus(){ //Null argument constructor, to set values to 0.
        AccessMenus.choice = 0;
    }

    public AccessMenus(int c){ //Single argument constructor.
        AccessMenus.choice = c;
    }

    public static void userMenu(){
        IBIO.output("1: Sell a product.");
        IBIO.output("2: Register a customer in the Loyalty programme.");
        IBIO.output("3: Stock check.");
        IBIO.output("4: Log out.");
        IBIO.output(" ");
        IBIO.output("Please make your choice: ");
        choice = IBIO.inputInt();
        if(choice == 1){
            //Go to Sales class.
        } else if(choice == 2){
            //Go to CustomerRegister class.
        } else if(choice == 3){
            //Open the StockCheck class.
        } else if(choice == 4){
            IBIO.output("Logging out.");
            System.exit(1);
        } else {
            IBIO.output("Invalid choice. Returning to menu.");
            userMenu(); //If the value entered does not correspond to any action, the program will treat it as invalid and return to the menu.
        }//close else
    }//close userMenu

    public static void adminMenu(){
        IBIO.output("1: Sell a product.");
        IBIO.output("2: Go to the specific object menus.");
        IBIO.output("3: Stock check.");
        IBIO.output("4: Order more stock.");
        IBIO.output("5: Register a customer in the Loyalty programme.");
        IBIO.output("6: Check Loyalty members.");
        IBIO.output("7: Create databases.");
        IBIO.output("8: Log out.");
        IBIO.output(" ");
        IBIO.output("Please make your choice: ");
        choice = IBIO.inputInt();
        if(choice == 1){
            //Go to Sales class.
        } else if(choice == 2){
          int createChoice = 0;
            IBIO.output("1: Video Games.");
            IBIO.output("2: DVD.");
            IBIO.output("3: CD.");
            createChoice = IBIO.inputInt("Enter choice: ");
            if(createChoice == 1){
                addVideoGame.vgMenu();
            } else if(createChoice == 2){
                //Go to addDVD class.
            } else if(createChoice == 3){
                //Go to addCD class.
            } else {
                IBIO.output("Invalid input.");
                adminMenu();
            }
        } else if(choice == 3){
            //Go to StockCheck class.
        } else if(choice == 4){
            //Go to StockOrder class.
        } else if(choice == 5){
            //Go to CustomerRegister class.
        } else if(choice == 6){
            //Go to LoyaltyCheck class.
        } else if(choice == 7){
            //Go to DatabaseCreation class.
        } else if(choice == 8){
            IBIO.output("Logging out.");
            System.exit(1);
        } else {
            IBIO.output("Invalid input. Returning to menu.");
            adminMenu();
        } //end else
    }//close AdminMenu
}//close AccessMenus

此外，这是 VideoGames 对象类，包含访问器和修改器方法以及主要字段等内容:

public class VideoGames implements java.io.Serializable {
    //Instance variables
    public static String title;
    public static int ageRating;
    public static String genre;
    public static String publisher;
    public static String developer;
    public static int quantity;

    public VideoGames(){ //null argument constructor
        VideoGames.title = null;
        VideoGames.ageRating = 0;
        VideoGames.genre = null;
        VideoGames.publisher = null;
        VideoGames.developer = null;
        VideoGames.quantity = 0;
    }//end VideoGames null argument constructor

    public VideoGames(String t, int aG, String g, String p, String d, int q){ //6-argument constructor
      VideoGames.title = t;
      VideoGames.ageRating = aG;
      VideoGames.genre = g;
      VideoGames.publisher = p;
      VideoGames.developer = d;
      VideoGames.quantity = q;
    }//end VideoGames 6-arguement constructor

    public VideoGames(VideoGames game){
        game = new VideoGames();
    }

    @Override
    public String toString(){
        return "\nTitle: " + title + " " + "\nPublisher: " + publisher + " " + "\nDeveloper: " + developer + " " + "\nAge Rating: " + ageRating + " " + "\nGenre: " + genre + " " + "\nQuantity: " + quantity + "\n ";
    }

    //Accessor and Mutator methods
public static String getTitle(){
    return title;
    }

public static void setTitle(String t){
        title = t;
    }

public static int getAgeRating(){
        return ageRating;
    }

public static void setAgeRating(int ag){ 
        ageRating = ag;
    }

public static String getGenre(){
        return genre;
    }

public static void setGenre(String g){  
        genre = g;
    }

    public static String getPublisher(){
        return publisher;
    }

    public static void setPublisher(String p){
        publisher = p;
    }

    public static void setDeveloper(String d){
        developer = d;
}
    public static String getDeveloper(){
        return developer;
        }
    public static void setQuantity(int q){
        quantity = q;
        }

    public static int getQuantity(){
        return quantity;
        }//end method setDeveloper
}//end class VideoGames

再次强调，我们将不胜感激任何帮助。

Answer 1

代码太多，我无法正确浏览，但听起来(快速扫描似乎证实了)您只创建了一个 VideoGames 对象。每当您更改该对象中的任何字段时，它都会更改该单个对象中的字段。

然后，您可以多次将同一个 VideoGames 对象添加到列表中，但这些都是对同一对象的单独引用。

相反，VideoGames 应该被称为 VideoGame 并包含一款游戏的数据，然后您应该创建一个 new VideoGame() 并进行设置每次您将一个添加到列表中时。

请记住，该列表仅包含对对象的引用，而不包含对象本身。

每个 VideoGames 对象就像街道上的房子。目前，您 build 一栋房屋并继续将该房屋的门涂成不同的颜色，而不是 build 多栋房屋并将每栋房屋的门涂成不同的颜色。

当您添加同一所房子 4 次时，您的列表只是一个地址列表，该列表只是重复相同的地址。

所以你正在做:

在地 block 1 build 房屋

1. 把房子的门漆成蓝色
2. 在列表中写下图 1
3. 把房子的门漆成绿色
4. 再次将图 1 添加到列表中
5. 把房子的门漆成红色
6. 再次将图 1 添加到列表中

现在您查看列表，您会看到三个条目 - 但当您查看门颜色时，它们都显示为红色。