我可以在超类的数组上调用子类吗？

Question

If I have an array of an object that has subclasses, can I access methods in the subclasses through calling the array?

This is a method in my Banking class, I would like to set the checking:

public void deposit() throws IOException {
BufferedReader br;
String entered_amount;

System.out.print("How much would you like to deposit? :");
br = new BufferedReader(new InputStreamReader(System.in));
entered_amount = br.readLine();
double amount = Double.valueOf(entered_amount).doubleValue();
balance = balance + amount;

System.out.println("Your balance is: " + getBalance());

Here is my Checking class:

public class Checking extends Bankaccount {

private double balance;

public Checking() {
}

public Checking(double balance) {
    this.balance = balance;
}

/**
 * @return the balance
 */
public double getBalance() {
    return balance;
}

/**
 * @param balance the balance to set
 */
public void setBalance(double balance) {
    this.balance = balance;
}

}

When calling baArray[0] in my main class is there a way to make deposit set the value of balance within the checking class?

The reason I'm doing this is because I'm writing out the array of objects to a file and rereading them when the program starts. I need to be able to store 3 sets of checking and savings. My deposit method would be what i'm trying to edit to use inheritance to set the balance in checking.

Answer 1

Add to your Banking class:

public abstract setBalance(double balance);

If you have subclasses of Banking besides the Checking class for which a setBalance method doesn't make sense, then you can implement the method and simply have it throw an exception. (It would seem to make sense for a Savings class to also have a setBalance method though.)

Alternatively, you can just move Checking 's setBalance method up to the superclass Banking , then Checking and Savings will both inherit the setBalance method. If you need to override them, you can, no problem.

EDIT: As per the comments to this answer, it's now more clear to me what you're trying to accomplish.

If you're intending to have an array of Banking objects, and each object has some unique account number, and for every Bank account, there is a Checking account and a Savings account, then logically, it sounds like it makes more sense for Checking and Savings to be private classes that can only be accessed through the Banking class.

So when an account holder goes to the bank, they open a Banking account. Perhaps by default this comes with 1 Checking account and 1 Savings account. These would be class variables in your Banking class:

private Checking checking;
private Savings savings;

Now your Banking class needs public methods to access the checking and savings accounts.

Let's say your Checking and Savings class both have a getBalance and setBalance . Now your Banking class would need a setter & getter for each type of account, and it just calls the appropriate method.

For example, in your Banking class:

public void setCheckingBalance(double balance)
{
    checking.setBalance(balance);
}

public double getCheckingBalance()
{
    return checking.getBalance();
}

Then in your main method, you'll use these methods via:

baArr[0].setCheckingBalance(100.00);