Question

如果此代码格式不正确，我会提前道歉，尝试粘贴而不是重新输入每一行。如果它不对，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.

我已经尝试将方法设置为静态，没有结果，并通过从标题中删除“静态”使主方法非静态，但随后我收到消息：java.lang.NoSuchMethodError: main Exception in thread "main"

有没有人有任何想法？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;
    }   
}

Answer 1

main是一种静态方法。它不能引用balance，它是一个属性（非静态变量）。 balance仅在通过对象引用（例如myAccount.balance或yourAccount.balance）引用时才有意义。但是当它通过类引用时没有任何意义（例如Account.balance（其余额是那个？）。

我对您的代码进行了一些更改，以便进行编译。

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;
}

Answer 2

行

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

你可能想要撤销并存入非静态的，并让它修改余额

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

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

并从通话中删除balance参数

Answer 3

撤回和存款的静态电话是您的问题。 account.withdraw（余额，2500）; 此行无法使用，因为“balance”是Account的实例变量。无论如何，代码没有多大意义，不会将提取/存入封装在Account对象本身内？所以退出应该更像是

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

当然，根据您的问题，您可以在此处进行额外验证，以防止出现负余额等。

Answer 4

您正试图直接从静态方法访问非静态字段，这在java中是不合法的。 balance是一个非静态字段，因此要么使用对象引用访问它，要么将其设置为静态。

Answer 5

只需写下：

private static double balance = 0;

你也可以写那些：

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

Answer 6

如果您愿意，可以保留撤销和存款方式，但是您必须像下面的代码一样编写。 sb =起始余额和eB =期末余额。

Account account = new Account(1122, 20000, 4.5);

    double sB = Account.withdraw(account.getBalance(), 2500);
    double eB = Account.deposit(sB, 3000);
    System.out.println("Balance is " + eB);
    System.out.println("Monthly interest is " + (account.getAnnualInterestRate()/12));
    account.setDateCreated(new Date());
    System.out.println("The account was created " + account.getDateCreated());

无法对非静态字段进行静态引用

6 个答案: