不能对非静态字段进行静态引用

Question

如果这段代码的格式不正确，我会提前道歉，尝试粘贴而不是重新输入每一行。如果不对，有人可以告诉我一次粘贴多行代码的简单方法吗？

我的主要问题是我不断收到一条错误消息： Cannot make a static reference to the non-static field balance.

我已经尝试使方法静态化，但没有结果，并通过从标头中删除“静态”使主要方法非静态化，但随后我收到消息： java.lang.NoSuchMethodError: main Exception in thread "main"

有人有什么想法吗？任何帮助表示赞赏。

 public class Account {

    public static void main(String[] args) {
        Account account = new Account(1122, 20000, 4.5);

        account.withdraw(balance, 2500);
        account.deposit(balance, 3000);
        System.out.println("Balance is " + account.getBalance());
        System.out.println("Monthly interest is " + (account.getAnnualInterestRate()/12));
        System.out.println("The account was created " + account.getDateCreated());
    }

    private int id = 0;
    private double balance = 0;
    private double annualInterestRate = 0;
    public java.util.Date dateCreated;

    public Account() {
    }

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

    public void setId(int i) {
        id = i;
    }

    public int getID() {
        return id;
    }

    public void setBalance(double b){
        balance = b;
    }

    public double getBalance() {
        return balance;
    }

    public double getAnnualInterestRate() {
        return annualInterestRate;
    }

    public void setAnnualInterestRate(double interest) {
        annualInterestRate = interest;
    }

    public java.util.Date getDateCreated() {
        return this.dateCreated;
    }

    public void setDateCreated(java.util.Date dateCreated) {
        this.dateCreated = dateCreated;
    }

    public static double withdraw(double balance, double withdrawAmount) {
        double newBalance = balance - withdrawAmount;
        return newBalance;
    }

    public static double deposit(double balance, double depositAmount) {
        double newBalance = balance + depositAmount;
        return newBalance;
    }
}

原文由 jshield 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 1

线条

account.withdraw(balance, 2500);
account.deposit(balance, 3000);

你可能想让取款和存款成为非静态的，让它修改余额

public void withdraw(double withdrawAmount) {
    balance = balance - withdrawAmount;
}

public void deposit(double depositAmount) {
    balance = balance + depositAmount;
}

并从调用中删除 balance 参数

原文由 ratchet freak 发布，翻译遵循 CC BY-SA 3.0 许可协议

Answer 2

main 是静态方法。它不能引用 balance ，它是一个属性（非静态变量）。 balance 只有在通过对象引用引用时才有意义（例如 myAccount.balance 或 yourAccount.balance ）。但是通过类引用的时候就没有任何意义了（比如 Account.balance （那是谁的余额？））

我对您的代码进行了一些更改，以便它可以编译。

 public static void main(String[] args) {
    Account account = new Account(1122, 20000, 4.5);
    account.withdraw(2500);
    account.deposit(3000);

和：

 public void withdraw(double withdrawAmount) {
    balance -= withdrawAmount;
}

public void deposit(double depositAmount) {
    balance += depositAmount;
}

原文由 wannik 发布，翻译遵循 CC BY-SA 3.0 许可协议