Problem with assigning an array to other array in Java
public class TestingArray {
public static void main(String[] args) {
int iCheck = 10;
int j = iCheck;
j = 11;
System.err.println("value of iCheck "+iCheck);
int[] val1 = {1,2,9,4,5,6,7};
int[] val2 = val1;
val2[0] = 200;
System.err.println("Array Value "+val1[0]);
}
}
Output:
value of iCheck 10
Array Value 200
From the above code, I found that if any array val2
is being assigned to another array val1
and if we change any value of val2
array, the result is as well reflected for the array val1
while the same scenario is not with variable assignment.
Why?
The following statement makes val2
refer to the same array as val1
:
int[] val2 = val1;
If you want to make a copy, you could use val1.clone()
or Arrays.copyOf()
:
int[] val2 = Arrays.copyOf(val1, val1.length);
Objects (including instances of collection classes, String
, Integer
etc) work in a similar manner, in that assigning one variable to another simply copies the reference, making both variables refer to the same object. If the object in question is mutable, then subsequent modifications made to its contents via one of the variables will also be visible through the other.
Primitive types (int
, double
etc) behave differently: there are no references involved and assignment makes a copy of the value.
Simply put, "val1" and "val2" are pointers to the actual array. You're assigning val2 to point to the same array as val1. Therefore, change one, and the other sees the same change. To have it truly be a copy, you'd have to clone the array instead of assigning.