Null Pointer Exception

[jonytek]

Can someone tell me why this tester is returning a null pointer exception??

I have just posted the tester. let me know if you require the complete program..

Thanks.

public class Tester {
	public static void main (String[] args)
	{
		ParkedCar[] p = new ParkedCar[9];
		p[0] = new ParkedCar("Nissan", "Pulsar", "Silver", "AF15ZA" );
		p[1] = new ParkedCar("Toyota", "Yarris", "Navy", "ASF123" );
		p[2] = new ParkedCar("Honda", "Civic", "Red", "SER456");
		p[3] = new ParkedCar("Suburu", "Forester", "White", "TIM879");
		p[4] = new ParkedCar("Suburu", "Outback", "White", "GOG987");
		p[5] = new ParkedCar("Ford", "Fiesta", "Green", "YIS432");
		p[6] = new ParkedCar("Fird", "Falcon", "Green", "JUL912");
		p[7] = new ParkedCar("Holden", "Commodore", "Silver", "FEG543");
		p[8] = new ParkedCar("Volvo", "S69", "Brown", "GHY459");                              
		                              
		p[0].setMinutesParked(135);
		p[1].setMinutesParked(35);
		p[2].setMinutesParked(65);
		p[3].setMinutesParked(105);
		p[4].setMinutesParked(2135);
		p[5].setMinutesParked(5);
		p[6].setMinutesParked(35);
		p[7].setMinutesParked(45);
		p[8].setMinutesParked(15);//sets time parked
		
		ParkingMeter[] pm = new ParkingMeter[9];
		pm[0] = new ParkingMeter(45);
		pm[1] = new ParkingMeter(55);
		pm[2] = new ParkingMeter(60);
		pm[3] = new ParkingMeter(135);
		pm[4] = new ParkingMeter(300);
		pm[5] = new ParkingMeter(5);
		pm[6] = new ParkingMeter(67);
		pm[7] = new ParkingMeter(34);
		pm[8] = new ParkingMeter(66);
		
		PoliceOfficer po = new PoliceOfficer("Jony cop", "123456A");
		
		for(int i = 0; i < p.length; i++)
		{
		ParkingTicket pt = po.examineCar(p[i], pm[i]);
		System.out.println(pt.issueTicket());
		}
	}
}

[subith86]

in which line do you get NullPointerException

[jonytek]

This is my error. Does this mean I have an error in line 42? Not sure.

Exception in thread "main" java.lang.NullPointerException
at Tester.main(Tester.java:42)

[subith86]

yes, exactly... and how do we know which is line 42 in your code unless you mention :p

[jonytek]

Ok line 42 is this line:

System.out.println(pt.issueTicket());

Here is the Class it relates to.

public class ParkingTicket {
	
	private String ticketDetails;
	
	
	public ParkingTicket(ParkedCar p , ParkingMeter pm, PoliceOfficer po)
	{
		int fine;
		int timeOver = p.getMinutesParked() - pm.getParkingTimePurchased();
		int hoursOver = timeOver / 60;
	
		if (timeOver > 1 && timeOver < 60)
		{
			fine = 25;
		}
		else
		{
			fine = 25 + hoursOver * 10;
		}
		ticketDetails ="****************************************\nYour car " + p.getMake()+ " " + p.getModel()+" " + p.getColor()+ " " + p.getRego();
		ticketDetails += "\nis fined $" + fine + " for exceeding time limit";
		ticketDetails += "\nThis fine is issued by " + po.getPoliceDetails();
		
	}
	public String issueTicket()
	{
		return ticketDetails;
	}
	
}

[subith86]

The problem is in this line

ParkingTicket pt = po.examineCar(p[i], pm[i]);

The method examineCar() returns a null value and the ParkingTicket reference "pt" is assigned a null value.

Now in line 42 you are trying access a method (issueTicket) in ParkingTicket class using the object "pt", but it is null. That's why you get NullPointerException.

So examine your examineCar() method ;) and analyze why it is returning null.