Why do i keep getting NullPointerException error

Question

public class Passenger {
String firstName;
String lastName;
int expenses;

public Passenger() {
firstName = "";
}

//Constructors
public Passenger(String cabinFirstName, String cabinLastName, int pExpenses)
{
firstName = cabinFirstName;
lastName = cabinLastName;
expenses = pExpenses;
}

public void setFirstName(String cabinFirstName)
{
firstName = cabinFirstName;
}

public String getFirstName()
{
return firstName;
}

public void setLastName(String cabinLastName) {
lastName = cabinLastName;
}

public String getLastName() {
return lastName;
}

public void setExpenses(int pExpenses) {
expenses = pExpenses;
}

public int getExpenses() {
return expenses;
}
}
public class Cabin {

int cabinNumber;

Passenger[] passenger = new Passenger[3];

public Cabin()
{

}

public Cabin(int cabinNumber, Passenger[] passenger)
{
this.cabinNumber = cabinNumber;
this.passenger = passenger;
}

public void setCabinNumber(int cNumber)
{
cabinNumber = cNumber;
}

public int getCabinNumber() {
return cabinNumber;
}

}

public class Main
{
public static Scanner scanner = new Scanner(System.in);
public static Cabin[] myShip = new Cabin[12];

public static void main(String[] args)
{

for (int count = 0; count < 12; count++)
{
myShip[count] = new Cabin();
}

myShip[0].passenger[0].setFirstName("a");

}

Answer 1

because Cabin.passenger[] array is empty
[null, null, null]
and
null.setFirstName("a")
causes error

//try
myShip[0].passenger[0] = new Passenger();
myShip[0].passenger[0].setFirstName("a");

Answer 2

Thanks