Constructor problem... JAVA

Cork24

Im learning OOP with JAVA since im new to Java and most of the class is used to it where going way to fast. for my liking..

we had a lab, every thing is working but cant get this part working

    public  boolean withdraw( double w ){
        withdraw = w;
        boolean ok;
        if(balance - w >= 0){
            balance = balance - w ;
            ok = true;
        } // end method if 
        else{ // open Else Statment, 
            System.out.printf("You dont have enough Money to Withdraw");
            ok = false;
        }// end method else 
        return(ok);
    }//end method Withdraw

public String toString(){
        String str;
        str = "Your Name is:" + " " + getName() + "\n" +
                "Your Starting Balance is:" + " " + balance + "\n" +
            "Your Account Number is:" + " " + getNumber() + " \n" +
            "Your Interest is:" + " " +  getInterest() + "\n" + 
                "Your Deposit was:" + " " + getDeposit() + "\n" +
                "Your Withdraw was:" + " " + withdraw + "\n" +
            "Your New Balance is:" + " " + getnBalance();
        return str;

the problem i have its still withdrawing money and giving my new Balance as -100 euro, i want it to stop and output " You do not have enough money" in that case..

BrokenArrows

Cork24 wrote: »

Im learning OOP with JAVA since im new to Java and most of the class is used to it where going way to fast. for my liking..

we had a lab, every thing is working but cant get this part working

    public  boolean withdraw( double w ){
        withdraw = w;
        boolean ok;
        if(balance - w >= 0){
            balance = balance - w ;
            ok = true;
        } // end method if 
        else{ // open Else Statment, 
            System.out.printf("You dont have enough Money to Withdraw");
            ok = false;
        }// end method else 
        return(ok);
    }//end method Withdraw

public String toString(){
        String str;
        str = "Your Name is:" + " " + getName() + "\n" +
                "Your Starting Balance is:" + " " + balance + "\n" +
            "Your Account Number is:" + " " + getNumber() + " \n" +
            "Your Interest is:" + " " +  getInterest() + "\n" + 
                "Your Deposit was:" + " " + getDeposit() + "\n" +
                "Your Withdraw was:" + " " + withdraw + "\n" +
            "Your New Balance is:" + " " + getnBalance();
        return str;

the problem i have its still withdrawing money and giving my new Balance as -100 euro, i want it to stop and output " You do not have enough money" in that case..

Looks like it should work.

Output the values of balance and w before the If condition to see what they are

cgarvey

Cork24 wrote: »

the problem i have its still withdrawing money and giving my new Balance as -100 euro, i want it to stop and output " You do not have enough money" in that case..

Your 'withdraw' method works as you want it to, so check your use of the method, and check that something else is not setting the 'balance' member variable elsewhere.

Are the values you are withdrawing non-integer? If so, are you running in to rounding issues (where 0.01 might not always be as you expect!). Take BrokenArrows's advice and print your values (before and after) to see. As an example if you start with a balance of 1.0, and withdraw 0.49 twice. You'd think you'd have 0.02 left, however it'll probably be something very slight above/below that value (0.020000000000000018 in my case). Compound that effect a few times, and you might end up with the issue you describe. I'm not sure that's likely to be the cause, however.

Two tips that may help in future:
1) Avoid naming member variables and methods the same thing. I.e. you appear to have "withdraw" as a class method (returns boolean), and as a class variable (of type double).
2) Use "this" in front of instance variables. Whilst not strictly necessary, it's good practice. For example, in your "withdraw" method, use "this.balance" to refer to the class instance's member variable, and not just "balance". It's better practice, because it makes the code easier to understand, and can help with compiler warnings if you have duplicate variable names, etc.

Axe Rake

Cork24 wrote: »

we had a lab, every thing is working but cant get this part working

    public  boolean withdraw( double w ){
        withdraw = w;
        boolean ok;
        if(balance - w >= 0){
            balance = balance - w ;
            ok = true;
        } // end method if 
        else{ // open Else Statment, 
            System.out.printf("You dont have enough Money to Withdraw");
            ok = false;
        }// end method else 
        return(ok);
    }//end method Withdraw

First of all, it might be best to clean up your method a little bit

This will make it easier to read and more logical:

public boolean withdraw(double amount) {        

    // if our withdrawal amount is <= than what we have in our account
    if(amount <= balance) {

        balance -= amount; //withdraw the amount
        return true;

    } else { // withdrawal amount is > than balance

        System.out.printf("You dont have enough Money to Withdraw");
        return false;
    } 
}

GCU Flexible Demeanour

cgarvey wrote: »

Two tips that may help in future:
1) Avoid naming member variables and methods the same thing. I.e. you appear to have "withdraw" as a class method (returns boolean), and as a class variable (of type double).
2) Use "this" in front of instance variables. Whilst not strictly necessary, it's good practice. For example, in your "withdraw" method, use "this.balance" to refer to the class instance's member variable, and not just "balance". It's better practice, because it makes the code easier to understand, and can help with compiler warnings if you have duplicate variable names, etc.

Just further on that, in your "toString" method, while you use getter methods to obtain the account number and some other details, you seem to be directly citing the "balance" and "withdraw(al)" variables. Its good practice to only operate on variables through (say) methods entitled "getBalance()" or "setBalance()".

This has the benefit of avoiding what may be the problem in this case - the possibility that the variable is being changed by some other block of code. If they've mentioned the OOP concept of encapsulation to you, this is what it means in practice - making your variables private to the class, and only accessing them through particular methods, helps to protect your data from getting messed with.

Cork24

ok,

This is the Full program..

Class BANK ACCOUNT

public class BankAccount {
 
    
    private String name;
    private int number;
    private double balance;
    private double deposit;
    private double withdraw;
    private double interest;
    private double nbalance;
    
    
        public BankAccount(String ip_name, double bal){
            name = ip_name;
            balance = bal;
            }
            public String getName(){
            return name;
            }
            
            public void number(int Acc){
                number = Acc;
                }
            
                public int getNumber(){
                return number;
                }
            
            public void interest (double i){
                
                interest = i/100 * balance;
            }

            public double getInterest(){
                return interest; 
            }

            public void Deposit(double d){
                deposit = d;
                }

                public double getDeposit(){
                return deposit;
                }

    
    public  boolean withdraw( double w ){
        withdraw = w;
        boolean ok;
        if(balance - w >= 0){
            balance = balance - w ;
            System.out.println("You have Withdraw:");
            ok = true;
        } // end method if 
        else{ // open Else Statment, 
            System.out.println("You dont have enough Money to Withdraw");
            ok = false;
        }// end method else 
        return(ok);
    }//end method Withdraw
    
    

    
    
    public void nbalance(double nbal){
        nbalance = balance + deposit + interest - withdraw; 
     } // end method nbalance
    
    public double getnBalance(){
    return nbalance;
    }//end method getnBalance
    
    
    
    public String toString(){
        String str;
        str = "Your Name is:" + " " + getName() + "\n" +
                "Your Starting Balance is:" + " " + balance + "\n" +
            "Your Account Number is:" + " " + getNumber() + " \n" +
            "Your Interest is:" + " " +  getInterest() + "\n" + 
                "Your Deposit was:" + " " + getDeposit() + "\n" +
                "Your Withdraw was:" + " " + withdraw + "\n" +
            "Your New Balance is:" + " " + getnBalance();
        return str;
    }//end method String
    
    }//end class BankAccount

Bank Account Test;

public class AccountTest {
    public static void main(String[] args){
    BankAccount account1, account2Account, account3;

    account1 = new BankAccount("David", 500);
    account1.number(230);
    account1.interest(.3);
    account1.Deposit(800);
    account1.withdraw(800);
    account1.nbalance(0);
    System.out.print(account1.toString()+"\n");

    
    
    
}
}

Sherfin

I think the problem is in your withdraw() method. When you try to withdraw(800) you are setting your withdraw variable to 800, but what happens if there is not enough money in the account ? When you go to calculate your balance and print your account.toString() it still has the 800 vaue

Cork24

Sherfin wrote: »

I think the problem is in your withdraw() method. When you try to withdraw(800) you are setting your withdraw variable to 800, but what happens if there is not enough money in the account ? When you go to calculate your balance and print your account.toString() it still has the 800 vaue

When i withdraw 800 its given me 500 left in the account,

But when i withdraw more then whats in the account it goes to negative number.

chrislad

Try if ((balance - w) >= 0) rather than (balance - w >= 0)

croo

When i withdraw 800 its given me 500 left in the account,

But when i withdraw more then whats in the account it goes to negative number.

I think you misunderstand what Sherfin is telling you...

If your code was

	    account1.withdraw(1500);
	    account1.nbalance(0);
	    System.out.print(account1.toString()+"\n");

When you call withdraw using 1500 you *will* get the message that "You don't have enough Money..."

But the attribute "withdraw" has still been set

public  boolean withdraw( double w ){
        withdraw = w;
...
...

Now you run nbalance with zero - which by the way makes little sense. You pass a value that is never used!
When you do this the nbalance is set as

nbalance = balance + deposit + interest - withdraw;

So even though the withdraw method failed you are still updating the balance because the attribute withdraw has been set to 1500.

I would echo what others have said
* using methods & attributes with the same names will only make debugging more difficult.
* look again at the idea of encapsulation

selfdiy

Just as a side note. When dealing with money numbers, use BigDecimals as doubles are not accurate enough.

srsly78

selfdiy wrote: »

Just as a side note. When dealing with money numbers, use BigDecimals as doubles are not accurate enough.

Double is fine for currency, float would be fine as well. Only need more accuracy for scientific calculations.

Giblet

srsly78 wrote: »

Double is fine for currency, float would be fine as well. Only need more accuracy for scientific calculations.

Absolutely false. Simple operations such as rounding after subtracting a percentage can cause issues.

Feathers

srsly78 wrote: »

Double is fine for currency, float would be fine as well. Only need more accuracy for scientific calculations.

Well, you could say you need them for accuracy for currency, but for precision for science

I thought the idea of BigDecimal for currency was to avoid rounding errors?

selfdiy

srsly78 wrote: »

Double is fine for currency, float would be fine as well. Only need more accuracy for scientific calculations.

Many years ago I found out the hard way that they are not fine...

Take a look here

http://www.mkyong.com/java/how-do-calculate-monetary-values-in-java-double-vs-bigdecimal/

BigDecimals are slower operating then primitive types, but when dealing with currencies accuracy is everything.

srsly78

Not false at all. Yes you have to watch out for rounding, but float maths is used all over finance. You should go into some investment bank and tell them they are doing it wrong

croo

srsly78 wrote: »

Not false at all. Yes you have to watch out for rounding, but float maths is used all over finance. You should go into some investment bank and tell them they are doing it wrong

That could explain a lot! :P

I've never seen java business software that uses double instead of Bigdecimal. Just google it the web is full of it. Or try it yourself

public class BigDecimalExample {
 
    public static void main(String args[]) throws IOException {
      
      //floating point calculation
      double amount1 = 2.15;
      double amount2 = 1.10;
      System.out.println("difference between 2.15 and 1.0 using double is: " + (amount1 - amount2));
    
      //Use BigDecimal for financial calculation
      BigDecimal amount3 = new BigDecimal("2.15");
      BigDecimal amount4 = new BigDecimal("1.10") ;
      System.out.println("difference between 2.15 and 1.0 using BigDecimal is: " + (amount3.subtract(amount4)));      
    }     
}
Output:
difference between 2.15 and 1.0 using double is: 1.0499999999999998
difference between 2.15 and 1.0 using BigDecmial is: 1.05

Read more: http://javarevisited.blogspot.com/2012/02/java-mistake-1-using-float-and-double.html#ixzz29U3lWz8d

clearz

Try this to set you on the right track

class BankAccount {

    private String name;
    private int accountNumber;
    private double balance;
    private double deposit;
    private double lastWithdrawl;
    private double interest;
    private double nbalance;


    public BankAccount(String name, double bal){
        this.name = name;
        this.balance = bal;
    }

    public double getBalance()
    {
        return balance;
    }

    public String getName(){
        return this.name;
    }

    public void setAccountNumber(int num){
        this.accountNumber = num;
    }

    public int getAccountNumber(){
        return this.accountNumber;
    }

    public void setInterest (double i){
        this.interest = i/100 * balance;
    }

    public double getInterest(){
        return this.interest;
    }

    public void setDeposit(double d){
        this.deposit = d;
    }

    public double getDeposit(){
        return this.deposit;
    }


    public  boolean withdraw( double w ){

        System.out.println("Withdrawing: EUR " + w);
        if(w <= balance){
            balance -= w ;
            System.out.println("You have Withdrawn: EUR " + w);
            lastWithdrawl = w;
            return true;
        } // end method if

        System.out.println("You dont have enough Money to Withdraw");
        return false;

    }//end method Withdraw





    public void updateBalance(){
        System.out.println("Updating Balance");
        balance = balance + deposit + interest - lastWithdrawl;
     } // end method nbalance




    public String toString(){
        String str;
        str = "Your Name is:" + " " + getName() + "\n" +
                "Your Starting Balance is:" + " " + getBalance() + "\n" +
            "Your Account Number is:" + " " + getAccountNumber() + " \n" +
            "Your Interest is:" + " " +  getInterest() + "\n" +
                "Your Deposit was:" + " " + getDeposit() + "\n" +
                "Your Withdraw was:" + " " + lastWithdrawl + "\n" +
            "Your New Balance is:" + " " + getBalance();
        return str;
    }//end method String

}//end class BankAccount

public class AccountTest {

    public static void main(String[] args){
        BankAccount account1, account2Account, account3;

        account1 = new BankAccount("David", 500);
        account1.setAccountNumber(230);
        account1.setInterest(.3);
        account1.setDeposit(800);
        account1.withdraw(800);

        System.out.println(account1.toString()+"\n");
        account1.updateBalance();

        System.out.println("Your New Balance is: "+ account1.getBalance());

        account1.withdraw(800);

        System.out.println("Your New Balance is: "+ account1.getBalance());
    }
}

Feathers

clearz wrote: »

Try this to set you on the right track

class BankAccount {

    private String name;
    private int accountNumber;
    private double balance;
    private double deposit;
    private double lastWithdrawl;
    private double interest;
    private double nbalance;


    public BankAccount(String name, double bal){
        this.name = name;
        this.balance = bal;
    }

    public double getBalance()
    {
        return balance;
    }

    public String getName(){
        return this.name;
    }

    public void setAccountNumber(int num){
        this.accountNumber = num;
    }

    public int getAccountNumber(){
        return this.accountNumber;
    }

    public void setInterest (double i){
        this.interest = i/100 * balance;
    }

    public double getInterest(){
        return this.interest;
    }

    public void setDeposit(double d){
        this.deposit = d;
    }

    public double getDeposit(){
        return this.deposit;
    }


    public  boolean withdraw( double w ){

        System.out.println("Withdrawing: EUR " + w);
        if(w <= balance){
            balance -= w ;
            System.out.println("You have Withdrawn: EUR " + w);
            lastWithdrawl = w;
            return true;
        } // end method if

        System.out.println("You dont have enough Money to Withdraw");
        return false;

    }//end method Withdraw





    public void updateBalance(){
        System.out.println("Updating Balance");
        balance = balance + deposit + interest - lastWithdrawl;
     } // end method nbalance




    public String toString(){
        String str;
        str = "Your Name is:" + " " + getName() + "\n" +
                "Your Starting Balance is:" + " " + getBalance() + "\n" +
            "Your Account Number is:" + " " + getAccountNumber() + " \n" +
            "Your Interest is:" + " " +  getInterest() + "\n" +
                "Your Deposit was:" + " " + getDeposit() + "\n" +
                "Your Withdraw was:" + " " + lastWithdrawl + "\n" +
            "Your New Balance is:" + " " + getBalance();
        return str;
    }//end method String

}//end class BankAccount

public class AccountTest {

    public static void main(String[] args){
        BankAccount account1, account2Account, account3;

        account1 = new BankAccount("David", 500);
        account1.setAccountNumber(230);
        account1.setInterest(.3);
        account1.setDeposit(800);
        account1.withdraw(800);

        System.out.println(account1.toString()+"\n");
        account1.updateBalance();

        System.out.println("Your New Balance is: "+ account1.getBalance());

        account1.withdraw(800);

        System.out.println("Your New Balance is: "+ account1.getBalance());
    }
}

Won't this subtract the withdrawal amount both on withdraw() and updateBalance() methods?

Also, seems strange to have getDeposit methods on a Bank Account alongside another method to read the balance…

clearz

@Feathers
The whole class is hideous to begin with. The code is meant as a push in the right direction than a completion of homework.