Java中如何实现多类间的数值共享，避免类调用时数值丢失？

问题根源 #

你现在数值丢失的核心原因有两个：

• 每个类都单独写了main方法作为入口，每次调用Work.main()或者Bank.main()的时候，方法内部都会new一个全新的Bank/Working实例，新实例的属性都是默认初始值0，之前的数值自然就没了
• 没有统一管理全局共享的状态（现金、银行余额、工作经验），不同类操作的不是同一个对象的属性

最简修改方案 #

不需要用到序列化，只要把共享对象的实例统一放在入口类Game里维护，所有功能方法都复用同一个实例即可，修改步骤如下：

第一步：删除Work、Bank类里的main方法，替换为普通业务方法 #

main方法是Java程序的启动入口，一个项目只需要一个入口就够了，我们把业务逻辑抽成普通方法，接收共享的状态对象作为参数：

改后的Work类

import java.util.Scanner;
public class Work extends Working {
    // 接收共享的bank实例、当前工作经验，返回更新后的工作经验
    public int startWork(Banking bank, int currentJobExperience) {
        Scanner input = new Scanner(System.in);
        int process = 0;
        int jobExperience = currentJobExperience;

        while (jobExperience == 0 && process == 0) {
            System.out.println("Welcome! Would you like to apply for a job? Y/N:");
            String response = input.next();

            if (response.equalsIgnoreCase("Y")) {
                jobExperience++;
            }
            else {
                System.out.println("Alright, see you next time!");
                process++;
            }
        }

        while (process == 0) {
            System.out.println("Welcome! Would you like to work? Y/N:");
            String response = input.next();

            if (response.equalsIgnoreCase("Y")) {
                System.out.println("How many hours would you like to work? 1-8:");
                int hours = input.nextInt();

                if (hours >= 1 && hours <= 8) {
                    setHours(hours);
                    setJob(jobExperience);
                    wageCalc();
                    setPaycheck();
                    // 操作的是同一个传入的bank实例，现金会累加
                    bank.setCash(bank.getCash()+getPaycheck());
                    printStatement();
                    jobExperience++;
                    process++;
                }
            }
            else {
                System.out.println("Alright, see you next time!");
                process++;
            }
        }
        return jobExperience;
    }
}

改后的Bank类

import java.util.Scanner;
public class Bank extends Banking {
    // 接收共享的bank实例
    public void startBank(Banking bank) {
        Scanner input = new Scanner(System.in);
        int process = 0;

        System.out.println("Thank you for banking with us. How can we help you?");
        while (process == 0) {
            System.out.println();

            System.out.println("Press 'B' to check your balance.  Press 'D' to deposit money. Press 'W' to withdraw money. Press 'E' to exit.");
            String response = input.next();

            if (response.equalsIgnoreCase("B")) {
                System.out.println("Your bank balance is currently $" + bank.getBalance());
                System.out.println("You currently have $" + bank.getCash() + " in cash.");
            }

            if (response.equalsIgnoreCase("D")) {
                System.out.println("How much would you like to deposit?");
                double amount = input.nextDouble();
                if (bank.getCash() >= amount) {
                    bank.setDeposit(amount);
                    bank.Deposit();
                    bank.setCash(bank.getCash() - amount);
                    System.out.println("You have deposited $" + bank.getDeposit() + ".");
                    System.out.println("Your new balance is $" + bank.getBalance());
                }
                else {
                    System.out.println("Sorry, you do not have enough cash to deposit.");
                }
            }

            if (response.equalsIgnoreCase("W") && bank.getBalance() > 0) {
                System.out.println("How much would you like to withdraw?");
                double amount = input.nextDouble();

                if (amount < bank.getBalance()) {
                    bank.setWithdraw(amount);
                    bank.Withdraw();
                    bank.setCash(bank.getCash() + amount);
                    System.out.println("You have withdrawn $" + bank.getWithdraw() + ".");
                    System.out.println("Your new balance is $" + bank.getBalance());
                }

                else {
                    System.out.println("You do not have sufficient funds to withdraw");
                    System.out.println("Your current balance is $" + bank.getBalance());
                }
            }

            else if (response.equalsIgnoreCase("W") && bank.getBalance() <= 0) {
                System.out.println("You do not have sufficient funds to withdraw");
            }

            if (response.equalsIgnoreCase("E")) {
                process = 2;
                System.out.println("Goodbye!");
            }
        }
    }
}

第二步：修改Game类，统一维护全局共享实例 #

把需要共享的Banking实例、工作经验都放在Game里管理，每次调用功能方法都传入同一个实例：

import java.util.Scanner;
public class Game {
   public static void main(String[] args) {
        Work work = new Work();
        Bank bank = new Bank();
        // 全局唯一的Banking实例，所有操作都用这一个
        Banking globalBank = new Banking();
        // 全局维护工作经验
        int globalJobExperience = 0;
        Scanner input = new Scanner(System.in);
        int process = 0;
        while (process == 0) {
            System.out.println("What would you like to do?");
            System.out.println("1) Go to the Bank");
            System.out.println("2) Go to Office Building");
            System.out.println("3) Exit Game");
            int response = input.nextInt();
            if (response == 1) {
                // 传入全局实例，操作的都是同一个对象的数值
                bank.startBank(globalBank);
            }
            if (response == 2) {
                // 传入全局实例，更新工作经验
                globalJobExperience = work.startWork(globalBank, globalJobExperience);
            }
            if (response == 3) {
                process++;
            }
        }
    }
}

第三步：原有Working、Banking类无需修改，直接使用即可 #

修改后所有现金、余额、工作经验都是在同一个实例上操作，不会再出现数值丢失的问题。如果后续需要加存档功能，再把全局的globalBank和globalJobExperience序列化存到本地文件即可，当前阶段不需要用到序列化。

内容的提问来源于stack exchange，提问作者sakshamp