How to create a simple spreadsheet in JAVA using jtable?

Question

I am having a hard time doing a simple spreadsheet in Java Using jtable here is my output

balance should be 14,750 - 250 which is 14,500. but the program is returning to -500 which i dont understand .

I tried to tweak my code regarding this but I just tend to mess it all up. here are the codes related to the balance. One thing to note that I used mysql to access the data from my database.

private void setBalance(int balance, int amount, String type) {
        if(type.equalsIgnoreCase("expense")) {
            balance = getBalance() - amount;
        }
        else if(type.equalsIgnoreCase("deposit")) {
            balance = amount;
        }
        else{
            balance = getBalance() + amount;
        }
        this.balance = balance;

    }

    public int getBalance() {

        return balance;
    }

//constructor for my transaction class
public Transaction(int transactionID, String transactionDetails, String transactionType, String purpose, int amount, Date date) {
        this.transactionID = transactionID;
        this.transactionDetails = transactionDetails;
        this.transactionType = transactionType;
        this.purpose = purpose;
        this.amount = amount;
        this.date = date;
        setBalance(getBalance(), amount, transactionType);
    }

There here are the codes where I add the values to my table

public void showTable() {
        ArrayList<Transaction>list = transactionList();
        DefaultTableModel model = (DefaultTableModel) table.getModel();
        Object row[] = new Object[7];

        for(int i = 0; i < list.size(); i++) {
            row[0] = list.get(i).getTransactionID();
            row[1] = list.get(i).getDate();
            row[2] = list.get(i).getTransactionDetails();
            row[3] = list.get(i).getTransactionType();
            row[4] = list.get(i).getPurpose();
            row[5] = list.get(i).getAmount();
            if(i == 0) {
            row[6] = list.get(i).getBalance();
            }
            else {
                row[6] = list.get(i).getBalance() - list.get(i-1).getBalance(); //in order to retrieve the previous balance
            }
            model.addRow(row);
        }

    }

Answer 1

the program is returning -500 which I don't understand

Ok, initial balance is 15000 then 2 transactions that should deduct 250 each

iteration balList balDisplay 
0          15000        15000 set by if(i == 0) {list.get(i).getBalance()}
1         +/-250        14750 set by else {list.get(1).getBalance() - list.get(0).getBalance}
2           250         -500 set by else {list.get(2).getBalance() - list.get(1).getBalance}

iteration 0 indicates that balance of list[0] was initially 15000

iteration 1 indicates that balance of list[1] was initially +250 or -250, displayed value is 14750 (15000-250). calculation is list.get(1).getBalance() - list.get(0).getBalance

• assuming it was +250, calculation gives -14750
• assuming it was -250, calculation gives -15250

Since the display displays 14750 it must display the calculated amount, but inverted (amount*-1), which is not included in the code snippets presented.

iteration 2: following from 1 we can assume, that balance of list[2] is initially +250, balDisplay should be 0 (250-250), but is -500.

Now one could start all over, assuming that initial balance is actually -15000, gets displayed as +15000 based on the reasoning in 1 etc...

This is what I could provide in reasonable time given the available information. The analysis suggests that the displayed balance of row 3 should be zero, but it is -500. There isn't anything available that would explain this. On the other hand, the balance also couldn't be 14500 either, based on the same reasoning.

What occured most suspicious was list.get(i).getBalance() - list.get(i-1).getBalance(). Why would one deduct one balance from another balance rather than an amount from some balance. And also, why deduct the earlier (i-1) balance from the later one (i)?