Declaring classes as Abstract

by: Stryker1990Posted on 2009-11-03 at 07:34:42ID: 25729913

Test class is this..

class bankTest
 
{
   public static void main ( String argv[] )
   {
      double interest;
 
      Account test = new Account();
      Account act = new Account(200.00);
      SavingsAccount sav = new SavingsAccount(1500.00, 0.0525);
      CheckingAccount chk = new CheckingAccount(145.38, 0.10);
 
      // Test constructors
      System.out.println("test account balance is " + test.getBalance() );
      System.out.println("act account balance is " + act.getBalance() );
      System.out.println("sav account balance is " + sav.getBalance() );
      System.out.println("sav account interest is " + sav.getInterestRate() );
      System.out.println("chk account balance is " + chk.getBalance() );
      System.out.println("chk account fee is " + chk.getFee() );
 
     // Test Account superclass
     act.credit(55.00);
     System.out.println("act balance is " + act.getBalance() );
     if (act.debit(75.00))
          System.out.println("act balance is " + act.getBalance());
     else
          System.out.println("No debit (would overdraw account)");
 
     if (act.debit(275.00))
          System.out.println("act balance is " + act.getBalance());
     else
          System.out.println("No debit (would overdraw account)");
 
     System.out.println("act balance is " + act.getBalance() );
 
     act.setBalance(12345.67);
     System.out.println("sav account balance is " + sav.getBalance() );
 
 
     // Test SavingsAccount
     sav.debit(250.00);
     System.out.println("sav account balance is " + sav.getBalance() );
     sav.credit(575.25);
     System.out.println("sav account balance is " + sav.getBalance() );
     interest = sav.calculateInterest();
     System.out.println("Interest is: " + interest);
     sav.credit(interest);
     System.out.println("sav account balance after interest is: " + sav.getBalance() );
     sav.setInterestRate(.065);
     System.out.println("new interest rate is " + sav.getInterestRate() );
     sav.setBalance(123456.78);
     System.out.println("sav account balance is " + sav.getBalance() );
 
     // Test CheckingAccount
     chk.credit(135.25);
     System.out.println("chk account balance is " + chk.getBalance() );
     chk.debit(123.45);
     System.out.println("chk account balance is " + chk.getBalance() );
     chk.debit(456.78);
     System.out.println("chk account balance is " + chk.getBalance() );
     chk.setFee(0.25);
     System.out.println("chk account fee is " + chk.getFee() );
     chk.setBalance(1234.56);
     System.out.println("chk account balance is " + chk.getBalance() );
 
   }
}

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by: Stryker1990Posted on 2009-11-03 at 07:35:20ID: 25729924

Account

public class Account {
    double Balance;
    public Account(){}
    public Account(double Balance) {
        this.Balance = Balance;
    }
 
 
    
    public void setBalance(double Balance) {
       this.Balance=Balance;
    }
 
 
    public double getBalance() {
        return Balance;
    }
 
    public double credit(double credit) {
 
        return Balance += credit;
    }
 
    public boolean debit(double debitamt)
{
if(getBalance()-debitamt<0)
return false;
setBalance(getBalance()-debitamt);
return true;
}
 
 
 
}

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by: Stryker1990Posted on 2009-11-03 at 07:35:55ID: 25729936

Checking Acc.

public class CheckingAccount extends Account {
    double fee;
    public CheckingAccount(double Balance, double fee) {
    this.fee = fee;
    this.Balance = Balance;
    }
 
public void setFee(double fee) {
    this.fee=fee;
}
 
public double getFee() {
    return fee;
}
 public boolean debit(double debitamt)
{
return super.debit(debitamt+getFee());
}
        
 
}

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by: Stryker1990Posted on 2009-11-03 at 07:36:31ID: 25729947

and Savings Acc.

public class SavingsAccount extends Account {
    double Interest;
     SavingsAccount(double Balance, double Interest) {
        super(Balance);
        this.Interest=Interest;
    }
 
 
public void setInterestRate(double Interest) {
    this.Interest=Interest;
}
public double getInterestRate() {
    return Interest;
}
double calculateInterest()
{
return getBalance()*getInterestRate();
}
 
 
}

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by: imladrisPosted on 2009-11-03 at 07:42:11ID: 25730008

If you make the credit and debit method in Account abstract, then you will have to provide implementations for both of those methods in both CheckingAccount and in SavingsAccount.

by: Stryker1990Posted on 2009-11-03 at 08:10:13ID: 25730391

Ah, thanks. That must be part of the problem. When it gives me the error for the methods "abstract methods cannot have a body", then where do I put the code? Or is it called for by putting the implementations in CheckingAccount and SavingsAccount as you suggest?

by: a_bPosted on 2009-11-03 at 08:26:13ID: 25730610

" it called for by putting the implementations in CheckingAccount and SavingsAccount as you suggest?"

That is correct. When you extend the abstract class,you have to implement the abstract methods in t hat class.

by: CEHJPosted on 2009-11-03 at 08:29:06ID: 25730648

There's possibly not much point in making those methods abstract really. They will only add to/subtract from the balance in each case

by: Stryker1990Posted on 2009-11-03 at 08:42:53ID: 25730792

There it is, working great, thank you a_b and imladris! :)

by: Stryker1990Posted on 2009-11-03 at 08:43:43ID: 31649464

tyvm! :)

by: a_bPosted on 2009-11-03 at 08:45:40ID: 25730832

@Stryker1990: I would urge you to look at the comment posted by CEJH as well. If all that the methods do is add and subtract then it would make more sense just to make those methods as concrete implementations in Account rather than duplicating the code in 2 classes.

by: objectsPosted on 2009-11-03 at 15:59:12ID: 25735230

> If all that the methods do is add and subtract then it would make more sense just to make those methods as concrete implementations in Account rather than duplicating the code in 2 classes.

It does make sense to make them abstract, the point of abstract is to force subclasses to implement the logic. The actual logic is actually irrelevant

by: imladrisPosted on 2009-11-03 at 16:27:09ID: 25735359

Quite. Although, in the current case, it appears there will be no difference between the two implentations or the credit and debit methods. If the methods are going to do the same thing in all (or even just most) of the classes, it will be more common, in practice, to just have them as methods in the base class.

by: Stryker1990Posted on 2009-11-03 at 20:00:00ID: 25736285

I do see all of your points about making the class and methods abstract or leaving them be, could be both redundant or useful. But part of what I was trying to do was understand how exactly abstract declarations worked altogether, further my knowledge in the language and you guys helped me do that. Much appreciated guys.

by: objectsPosted on 2009-11-03 at 20:15:23ID: 25736354

thats right, its about the concept of abstract not the particulars of the example.

by: CEHJPosted on 2009-11-04 at 01:41:25ID: 25737695

A good compromise would be to make an adjustBalance(double) abstract method and have concrete implmentations of debit(double) and credit(double). This would cut down on the coding AND enable you to make adjustments for different types of account. Both credit and debit would call adjustBalance

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Declaring classes as Abstract

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