using the return of a method to initialize an ArrayList

**mia_tech** · October 25th, 2012, 02:41 PM

how could I use the return of extractCustomers and initialze ArrayList<Customer> in main method?

import java.util.*;
 
public class Main {
 
 
	public static void main(String[] args) {
 
		ArrayList<BankAccount> allAccounts = new ArrayList<BankAccount>();
 
		Customer john = new Customer();
		john.firstName = "John";
		john.lastName = "Doe";
 
		BankAccount johnBa = new BankAccount();
		johnBa.accNumber = "111-222-333";
		johnBa.balance = 200;
		johnBa.myCustomer = john;
 
		Customer nick = new Customer();
		nick.firstName = "Nick";
		nick.lastName = "James";
 
		BankAccount nickBa = new BankAccount();
		nickBa.accNumber = "222-333-444";
		nickBa.balance = 100;
 
		allAccounts.add(johnBa);
		allAccounts.add(nickBa);
 
		ArrayList<Customer> allCust;
 
	}
 
	static ArrayList<Customer> extractCustomers(ArrayList<BankAccount> ba) {
		ArrayList<Customer> cu = new ArrayList<Customer>();
 
		for(BankAccount b: ba) {
			cu.add(b.myCustomer);
		}
 
		return cu;
	}
 
}

**mia_tech** · October 25th, 2012, 03:04 PM

ok I got it, but now I'm trying to output the content of allCust ArrayList and I'm getting nullPointerException.... could someone give me a hint? Thanks

import java.util.*;
 
public class Main {
 
 
	public static void main(String[] args) {
 
		ArrayList<BankAccount> allAccounts = new ArrayList<BankAccount>();
 
		Customer john = new Customer();
		john.firstName = "John";
		john.lastName = "Doe";
 
		BankAccount johnBa = new BankAccount();
		johnBa.accNumber = "111-222-333";
		johnBa.balance = 200;
		johnBa.myCustomer = john;
 
		Customer nick = new Customer();
		nick.firstName = "Nick";
		nick.lastName = "James";
 
		BankAccount nickBa = new BankAccount();
		nickBa.accNumber = "222-333-444";
		nickBa.balance = 100;
 
		allAccounts.add(johnBa);
		allAccounts.add(nickBa);
 
		ArrayList<Customer> allCust = new ArrayList<Customer>();
		allCust = extractCustomers(allAccounts);
 
		for(Customer c : allCust) {
			System.out.println(c.firstName+" "+c.lastName);
		}
 
	}
 
	static ArrayList<Customer> extractCustomers(ArrayList<BankAccount> ba) {
		ArrayList<Customer> cu = new ArrayList<Customer>();
 
		for(BankAccount b: ba) {
			cu.add(b.myCustomer);
		}
 
		return cu;
	}
 
}

public class BankAccount {
 
	String accNumber;
	double balance; 
 
	Customer myCustomer;
 
}

public class Customer {
 
	String firstName;
	String lastName;
 
}

**jps** · October 25th, 2012, 03:29 PM

Do you know what a NullPointerException is? Do you understand what the error message is telling you? The line number* to the error is included in the message.

The best advice I have for this is to understand how to read the error message. Simple mistakes like this are common and understanding the error message details will be a useful skill.
If you can not figure it out, copy paste the error message for help.

*The number is not always exactly the line the error is on, but this is not the place for that topic.

**mia_tech** · October 25th, 2012, 05:05 PM

Originally Posted by jps

Do you know what a NullPointerException is? Do you understand what the error message is telling you? The line number* to the error is included in the message.

The best advice I have for this is to understand how to read the error message. Simple mistakes like this are common and understanding the error message details will be a useful skill.
If you can not figure it out, copy paste the error message for help.

*The number is not always exactly the line the error is on, but this is not the place for that topic.

I just figure out what I was missing!

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