Java 오류 \'비정적 필드에 대한 정적 참조를 만들 수 없습니다\'가 발생하는 이유는 무엇입니까?

<code class="java">public class Account {

    // Static variables
    public static int id = 0;
    public static double annualInterestRate = 0;
    public static java.util.Date dateCreated;

    // Non-static variables
    private double balance = 0;

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

        // Overloaded methods (static)
        double newBalance = withdraw(account.balance, 2500);
        newBalance = deposit(newBalance, 3000);

        System.out.println("Balance is " + account.getBalance());
        System.out.println("Monthly interest is " + (account.annualInterestRate / 12));
        System.out.println("The account was created " + account.getDateCreated());
    }

    // Overloaded methods
    public static double withdraw(double balance, double withdrawAmount) {
        balance -= withdrawAmount;
        return balance;
    }

    public static double deposit(double balance, double depositAmount) {
        balance += depositAmount;
        return balance;
    }
}</code>