How to Implement IComparable interface?

Question

I am populating an array with instances of a class:

BankAccount[] a;
. . .

a = new BankAccount[]
{
    new BankAccount("George Smith", 500m),
    new BankAccount("Sid Zimmerman", 300m)
};

Once I populate this array, I would like to sort it by balance amounts. In order to do that, I would like to be able to check whether each element is sortable using IComparable.
I need to do this using interfaces. So far I have the following code:

public interface IComparable
{
    decimal CompareTo(BankAccount obj);
}

But I'm not sure if this is the right solution. Any advice?

Answer 1

You should not define IComparable yourself. It is already defined. Rather, you need to implement IComparable on your BankAccount class.

Where you defined the class BankAccount, make sure it implements the IComparable interface. Then write BankAccount.CompareTo to compare the balance amounts of the two objects.

public class BankAccount : IComparable<BankAccount>
{
    [...]

    public int CompareTo(BankAccount that)
    {
        if (this.Balance <  that.Balance) return -1;
        if (this.Balance == that.Balance) return 0;
        return 1;
    }
}

---

Edit to show Jeffrey L Whitledge's solution from comments:

public class BankAccount : IComparable<BankAccount>
{
    [...]

    public int CompareTo(BankAccount that)
    {
        return this.Balance.CompareTo(that.Balance);
    }
}