Question

public class Account
{
static int accountNum;
static int nextAccountNum = 112200;
static double balance;


    public static void main(String args[])
    {
        Account checkingAccount = new Account(1500.00);
        Account savingAccount = new Account(1000.00);
        Account moneyMarketAccount = new Account(500.00);

        checkingAccount.getAccountNumber();
        savingAccount.getAccountNumber();
        moneyMarketAccount.getAccountNumber();

    }

    public Account(double bal)
    {
        balance = bal;
        accountNum = nextAccountNum;
        nextAccountNum++;
    }

}

每次运行它时，我都没有得到任何返回变量。我所看到的只是过程完成的文本。寻求帮助

Answer 1

你没有输出任何东西。使用System.out.println输出帐户余额，例如

System.out.println(checkingAccount.getAccountNumber());

另外，请将您的accountNum和balance变量设为非static，否则每个新实例都会覆盖余额和帐号。

Answer 2

将主函数与将具有多个实例的类分开通常是一种好习惯。 getters和setters方法用于正确封装类变量，因为帐户可能应该具有。下面是一个例子。

<强> Main.java

public class Main {
    public static void main(String args[])
    {
        Account checkingAccount = new Account(1,1500.00);
        Account savingAccount = new Account(2,1000.00);
        Account moneyMarketAccount = new Account(3,500.00);

        System.out.println("Account " + checkingAccount.getAccountNumber() 
                + " has balance of: " + checkingAccount.getBalance());
        System.out.println("Account " + savingAccount.getAccountNumber() 
                + " has balance of: " + savingAccount.getBalance());
        System.out.println("Account " + moneyMarketAccount.getAccountNumber() 
                + " has balance of: " + moneyMarketAccount.getBalance());
    }
}

<强> Account.java

public class Account
{
private int accountNum;
private int nextAccountNum = 112200;
private double balance;

    public Account(int accountNum, double balance)
    {
        this.balance = balance;
        this.accountNum = accountNum;
    }

    public int getAccountNumber() {
        return accountNum;
    }

    public double getBalance() {
        return balance;
    }

    public void setBalance(int balance) {
        // check if balance variable is a correct value
        // before setting it to the class variable
        this.balance = balance;
    }

}

Answer 3

一个问题是accountNum和balance被声明为static。您需要它们作为实例字段，因此Account的每个实例都有自己的值。

您没有输出的原因是您的main()方法会创建多个Account对象但不对它们执行任何操作。

public class Account
{
    static int nextAccountNum = 112200;
    int accountNum;
    double balance;

    public static void main(String args[])
    {
        Account checkingAccount = new Account(1500.00);
        Account savingAccount = new Account(1000.00);
        Account moneyMarketAccount = new Account(500.00);

        checkingAccount.getAccountNumber();
        savingAccount.getAccountNumber();
        moneyMarketAccount.getAccountNumber();

        System.out.println("Checking: " + checkingAccount.toString());    
        System.out.println("Savings: " + savingAccount.toString());    
        System.out.println("Money market: " + moneyMarketAccount.toString());    
    }

    public Account(double bal)
    {
        balance = bal;
        accountNum = nextAccountNum;
        nextAccountNum++;
    }

    @Override
    public String toString() {
        return "Account " + accountNum + ": balance=" + balance;
    }    
}

无法返回变量java

3 个答案: