If I have a 2d array of objects, and want to initialize them all, I call a loop, eg:
for(int i=0; i<len; i++)
for(int j=0; j<len; j++)
objects[i][j] = new MyObject();
Which works fine, but when I tried doing this with the for-each construct, it didn't work and the entire array remains null:
for(MyObject[] intermediate: objects)
for(MyObject obj: intermediate)
obj = new MyObject();
How come they behave differently?
The assigment
obj = new MyObject();
just set a new object in the variable obj, and does not change the value in the array, it only changes the reference variable obj.
What happens is that objects[i][j] is assined to obj, and then you change the value of obj, without changing the actual array.
when you assign directly to objects[i][j] - it works as expected, since you change the value of objects[i][j], which is exactly what you want to do.
References are passed by value, so obj = new MyObject(); only updates the local copy of your reference to objects[i][j].
It only works for the outer loop, because there are new references being made, but not deep ones:
public static void main (String[] args ) {
Integer [][] iaa = new Integer[3][4];
for (Integer[] ia : iaa) {
for (int i = 0; i < ia.length; ++i) {
ia[i] = i;
}
}
}
