Question

I writing an application where i use an array within a class. This array is declared globally outside of any method scope so that all of the objects methods will be able to access the data. However, when i assign an object to a index that object is only available as a part of the array in that particular method. Any other method trying to read that index of the array gets a nullpointerexception.

Some code illustrating my usage:

Account[] accounts = new Account[8000];


public void addAccount() {


    cli.printMessage("Welcome to the account add wizard.");
    String holdername = cli.getInput(entername);
    int accountnr = Integer.parseInt(cli.getInput(enternr));
    BigDecimal accbalance = new BigDecimal(cli.getInput(enterinitialbalance));

    accounts[accountnr] = new Account(holdername, accountnr, accbalance);
    String accountinfo=accounts[accountnr].number + " " + " " + accounts[accountnr].holder + " " + accounts[accountnr].balance;
    cli.printMessage(accountinfo);

}

Adding the account works all the way, this do not when ran from the same instance of this class:

public void getAccountinfo() {

    int accountnr = Integer.parseInt(cli.getInput(getinfo));
    String accountinfo=accounts[accountnr].number + "" + "" + accounts[accountnr].holder + accounts[accountnr].balance;
    cli.printMessage(accountinfo);
}

Is this due to scope or is it due to me confusing instance and class variables? Might it be something completely different?

The error i get is a nullpointer exception at

        String accountinfo=accounts[accountnr].number + "" + "" + accounts[accountnr].holder + accounts[accountnr].balance;

Grateful for any help!

Answer 1

In getAccountInfo you let the user input a number X.
If the array ‘cell’ at X was not previously set via addAccount, accounts[X] is null and thus accounts[X].number correctly bombs out.