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up vote -2 down vote favorite

this is a homework problem and it is giving me null pointer exception when i run the tester. the error seems to be in my line 

balance[i]=InitialBalance;

 

public class Bank
{

    private BankAccount[] accounts;
    private double [] balance;
    int NumbersOfBankAccount;
    double InitialBalance;
    public Bank (int x, double y )
    {
        NumbersOfBankAccount = x;
        InitialBalance = y;

    }


    /**
     *     This method will get balance of specified bank account.
     */
    public double getBalance(int index)
    {
        for(int i = 0; i <NumbersOfBankAccount; i++)
        {
            balance[i]=InitialBalance; 
        }
        System.out.println(balance);
        return balance[index]; 
    }
}
share|improve this question
    
If you fix the errors as mentioned in the answers, your getBalance will always return InitialBalance (provided that index is within array range). –  jlordo Nov 5 '12 at 22:13
    
for the future, just always know that nullpointerexception always points to using something with a null value-the most common being something not initialized properly. –  Jimmt Nov 5 '12 at 22:52

5 Answers 5

up vote 7 down vote

balance and accounts are never initialized.

You are missing something like this in your constructor:

balance = new double[NumbersOfBankAccount];
accounts = new BankAccount[NumbersOfBankAccount];
share|improve this answer
up vote 5 down vote

balance isn't initialized.

private double [] balance;

Here's a fix:

public Bank (int x, double y )
{
    NumbersOfBankAccount = x;
    balance = new double[NumbersOfBankAccount];
    accounts = new BankAccount[NumbersOfBankAccount];
    InitialBalance = y;

}

Also, NumbersOfBankAccount is a long name and tedious to type out. You should change that to numAccounts or something like that.

And another thing: by convention, variable names typically start with a lowercase letter. (InitialBalance should be initialBalance)

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up vote 1 down vote

you dint initialize your balance; array and trying to access its indexes.

you have to initilize your array like this:

private double [] balance = new double[sizeofyour array] ;
share|improve this answer
up vote 1 down vote

You have to initialize your array 'balance' first:

balance = new double[ NumbersOfBankAccount ];
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up vote 0 down vote

You'll need to make sure that your NumbersOfBankAccount variable is at least as big as the balance array. Did you remember to initialize the array? Also doesn't look like you're using your accounts array.

Also, look at the comment for you getBalance method. I don't think it's doing what you want it to do. Looks like you want to to use the index passed to get the balance of the account specified by the accounts array. Or are you doing the for loop for testing (which is okay)?

So recap:

  1. Make sure your arrays are initialized
  2. make sure that you're getting data from the right array
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