Suppose I have
int[] array = new int[] {1, 2, 3};
Method method = // something
// int element2 = array[2]; // non-reflection version
int element2 = (int) method.invoke(array, 2); // reflection version
How to fill method variable so that it get array element by index?
Java doesn't add new methods to arrays. Only methods available from arrays are those inherited from Object class, and there is none like array.get(index) which we could use via:
method.invoke(array,index)
That is why reflection package has utility class java.lang.reflect.Array, which contains methods like public static Object get(Object array, int index) and overloaded versions for primitive types like public static int getInt(Object array, int index). It also contains corresponding set(array, index, value) methods.
With those we can write code like
int[] array = new int[] {1, 2, 3};
int element2 = Array.getInt(array, 2);//reflective way
//or
//int element2 = (int) Array.get(array, 2);//reflective way
System.out.println(element2);
int[] array = new int[] {1, 2, 3};
Method method = ...................// something
// int element2 = array[2]; // non-reflection version
int element2 = (int) method.invoke(array, 2); // reflection version
then probably author of puzzle wants you to reflectively call Arrays.get(array,index). In other words method should represent
Method method = Array.class.getDeclaredMethod("get", Object.class, int.class);
But this would also require calling that method either on Array.class or on null (since it is static), so we would also need to modify
int element2 = (int) method.invoke(array, 2);
and add as first argument
int element2 = (int) method.invoke(Array.class, array, 2); // reflection version
^^^^^^^^^^^
OR
int element2 = (int) method.invoke(null, array, 2); // reflection version
^^^^
method.invoke() otherwise this is also an answer array[2]
Method and get is static. So, there is no (non-static) method which can obtain element of an array?Try with List
int[] array = new int[] { 1, 2, 3 };
// create a List and populate
List<Integer> list = new ArrayList<Integer>();
for (int i : array) {
list.add(i);
}
// use reflection method get/set on List
Method method = List.class.getDeclaredMethod("get", new Class[] { Integer.TYPE });
Object element2 = method.invoke(list, 2); // reflection version
System.out.println(element2); // output 3
get method. you can try with List.List
Methodwhich returns element of an arraymethod.invoke(null, array, 2);instead.