I'm trying to build an array of objects, but getting a nullpointer exception when trying to set them.
Why when it gets to the first cars[i], it throws the exception?
Here is the code: Example 1: http://pastebin.com/4h4W3770 Example 2: http://pastebin.com/4GL4FhrW
When you create an array object, all its element are initialized to null (if array contains subclass of java.lang.Object). You need to instantiate each element before accessing any property . You are trying to set Cars property without instantiating it in the code below which is causing NullPointerException:
car[i].setPlate(info[0]);
Before doing this you need to initialize an instance of Car like this:
public static void main(String[] args) {
String sCurrentLine;
try (BufferedReader br = new BufferedReader(new FileReader("cars.txt"))) {
while ((sCurrentLine = br.readLine()) != null) {
String[] info = sCurrentLine.split(",");
for (int i = 0; i < 10; i++) {
car[i] = new Cars(); //instantiate Cars object or next statement will throw NPE
car[i].setPlate(info[0]);
car[i].setLocation(Integer.parseInt(info[1]));
car[i].setSpeed(Integer.parseInt(info[2]));
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
Your setter methods dont get any input / parameters, so they dont know what they should set:
public void setSpeed() {
this.speed = speed;
}
Change to:
public void setSpeed(Integer speed) {
this.speed = speed;
}
You have a simple problem. you have never initialised car[i]. car[i] is null and when you try any operation to a variable that is null you get a NullPointerException.
So the solution is to initialise car[i] As shown below:
for (int i = 0; i < 10; i++) {
car[i] = new Cars(); //intialise the car.
car[i].setPlate(info[0]);
car[i].setLocation(Integer.parseInt(info[1]));
car[i].setSpeed(Integer.parseInt(info[2]));
}
This I think will solve your problem.
