How to use a static variable from a class to update a non-static instance variable in another class?

Question

Hello I am working on this homework and it's almost done but one thing doesn't work well. I created these two classes "SavingAccount" and "TimeAccount", subclasses of "Account" and they have different type of interest calculations that includes current time and time that account last updated. I have a time variable which is modeled as months and it's declared as zero in my Test class. And whenever i deposit, withdraw or transfer money it should update the accounts lastTimeUpdated variable and make it equal to currentMonth. Here's my Test class:

public class Test {

    public static int month = 0;

    static void click(){
        month++;
        System.out.println("Current month is " + month);
    }

    static void click(int x){
        month += x;
        System.out.println("Current month is " + month);
    }


    public static void main(String[] args) {

        Customer ali = new Customer("Ali");
        Customer veli = new Customer("Veli");
        Customer elif = new Customer("Elif");

        click();

        Account savingAccount1 = new SavingAccount(ali, garanti, 3);
        Account timeAccount1 = new TimeAccount(elif, akbank);

        click();

        savingAccount1.deposit(500);
        timeAccount1.deposit(400);

        click(5);

        System.out.println(savingAccount1.getLastUpdate());
        System.out.println(timeAccount1.getLastUpdate());


    }


}

And in output it says their last time updated is still 1 although i called click() method a couple of times and deposited some money in them.

This is my deposit method and it should change its lastUpdated variable to currentTime but it doesn't.

public abstract class Account {

    protected int currentTime = Test.month;
    protected int timeUpdated;

    public abstract double getBalance();

    public void deposit(double amount){
        balance = this.getBalance();
        balance += amount;
        timeUpdated = currentTime;
    }
}

This is getBalance() method for each subclasses, since they have different kind of interest calculations:

public class SavingAccount extends Account {

    private final int term;
    private static int number = 1;
    private final double interestRate = 0.2;

    public SavingAccount(Customer c, Bank b, int t){
        super(c, b, 0, number);
        term = t;
        number++;   
    }

    @Override
    public double getBalance() {
        double a = (1+term*interestRate/12);
        double b = (currentTime-timeUpdated)/term;
        balance = balance*Math.pow(a,b);
        return balance;
    }

}

and

public class TimeAccount extends Account {

    private static int number = 1;
    private final double interestRate = 0.1;

    public TimeAccount(Customer c, Bank b){
        super(c, b, 1, number);
        number++;   
    }

    public double getBalance(){
        double a = 1+interestRate/12;
        double b = currentTime-timeUpdated;
        balance = balance*Math.pow(a,b);
        return balance;
    }

}

I know this is long but i tried to make it clear to find where the problem is and my other question is marked as "duplicate" but i couldn't find the answer.

So my program doesn't update the lastUpdated time, that's why interests won't work. Thanks in advance.

Answer 1

Assigning a static variable doesn't continuously update.

protected int currentTime = Test.month;

This sets the value of currentTime to whatever Test.month was when the Account was created. If you want it to change, you have to update it.

Answer 2

看来您只是在初始化currentTime时才设置它，因此一旦创建了Account对象，它的currentTime就固定了，并且不会随着Test.month更改而更新。

Answer 3

You are only assigning currentTime once (at instantiation). It will not automatically update when you update Test.month. You need a mechanism to update the time in each of your instances of Account and call it in each place you call click. Really, the Test.month member is not particularly useful.