September 22nd, 2010, 03:10 PM
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Join Date: Sep 2010
Posts: 8
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Homework - Exception in thread "main" java.lang.NullPointerException
So, i am trying to build a simple database (array of Car type).
the code is quite simple but for some reason i keep getting the same error after running the program (compiling went through). so i have 3 classes:
PHP Code:
class DataBase {
private Car[] database = new Car[3];
public DataBase() {
for (int i=0; i<database.length; i++) {
database[i].formatCar();
}
}
public void addCar(Car car1) {
for (int i=0; i<database.length; i++) {
if (database[i].getModel()=="empty") {
database[i]=car1;
}
}
}
public void printDataBase() {
int i=0;
while (i<database.length) {
database[0].printCar();
i=i+1;
}
}
}
PHP Code:
class mainpage {
public static void main (String[] args) {
Car car1 = new Car();
DataBase database1 = new DataBase();
car1.setCar();
database1.addCar(car1);
database1.printDataBase();
}
}
PHP Code:
import java.util.*;
class Car {
private String _model;
private String _color;
private int _year;
private Scanner _input = new Scanner(System.in);
public Car() {
_model = "empty";
_color = "empty";
_year = 0;
}
public void setCar() {
System.out.print("Enter model: ");
_model = _input.next();
System.out.print("Enter color: ");
_color = _input.next();
System.out.print("Enter year: ");
_year = _input.nextInt();
}
public void formatCar() {
_model = "empty";
_color = "empty";
_year = 0;
}
public String getModel() {
String model=_model;
return model;
}
public String getColor() {
String color=_color;
return color;
}
public int getYear() {
int year=_year;
return year;
}
public void printCar() {
System.out.println("Model :"+_model);
System.out.println("Color :"+_color);
System.out.println("Year :"+_year);
}
}
And the error i get:
PHP Code:
yotam@main computer:~/Documents/java/newcar$ java mainpage
Exception in thread "main" java.lang.NullPointerException
at DataBase.<init>(DataBase.java:7)
at mainpage.main(mainpage.java:5)
yotam@main computer:~/Documents/java/newcar$
i searched for possible reasons and i came across the possibility that the array wasn't initialized, but then i changed to constructor to set model and color to "empty" and year to 0.
so now i have no clue, need your help guys.
Thanks!
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