Hi there i'm creating a small game for school, but when i try to do this to fill out the x and y variables in this array i get a NPE. Could anyone help?
public class mainclass {
public static void main(String[] args) {
Gra piece[] = new Gra[10];
for (int i = 0; i < piece.length; i++) {
piece[i].x = 50;
piece[i].y = 50;
}
}
}
class Gra{
public int x = 50;
public int y = 10;
}
Gra piece[] = new Gra[10];
does not initialize objects inside the array, it only creates array, so call constructor to create Gras
for (int i = 0; i < piece.length; i++) {
piece[i] = new Gra();
piece[i].x = 50;
piece[i].y = 50;
}
The statement
Gra piece[] = new Gra[10];
will only initialize the array. It won't create Gra objects.
Inside the for loop, you still have to call the constructor as
for (int i = 0; i < piece.length; i++) {
piece[i] = new Gra();
piece[i].x = 50;
piece[i].y = 50;
}
Also, read more about encapsulation. Its a bad idea to make instance variables public.
You have initialized gra array but you did not create Object so there is no Object inside the array and by default null is initialized, so piece[i].x is actually null.x which throws NPE.
Gra piece[] = new Gra[10];
for (int i = 0; i < piece.length; i++) {
piece[i] = new Gra();
piece[i].x = 50;
piece[i].y = 50;
}
You have created a an array of Gra with 10 elements.
Gra piece[] = new Gra[10];
But each element in that array is currently pointing to null.
You need to initialize those individual elements as Java's default value for Object is null.
Because you are just creating Array of type Gra By
Gra piece[] = new Gra[10];
So by default this is null .
So first initialize them like
for (int i = 0; i < piece.length; i++) {
pirce[i] = new Gra();
}
Then do
for (int i = 0; i < piece.length; i++) {
piece[i].x = 50;
piece[i].y = 50;
}
