import java.lang.reflect.Array;
import java.util.Arrays;

class Main {
    public static void main(String[] args) {
        FastClearArray<Integer> a = new FastClearArray<>(Integer.class, 10);
        System.out.println(a.put(1, 3) + " | " + a.get(2));
        System.out.println(a.get(1) + " | " + a.get(2));
        a.clearAll();
        System.out.println(a.get(1) + " | " + a.put(2, 6));
        System.out.println(a.put(1, 9) + " | " + a.get(2));
        System.out.println(a.get(1) + " | " + a.get(2));
        a.clearAll();
        System.out.println(a.get(1) + " | " + a.get(2));
    }
}

public class FastClearArray<T> {

    private final T[] arr;
    /**
     * deceleration of masterModCount range exhaustion
     */
    private boolean modified;
    /**
     * aka modCount in Collections
     * 18.5 sextillion of values - Hopefully, that's enough.
     */
    private long masterModCount = Long.MIN_VALUE;
    private long[] modCount;

    public FastClearArray(Class<T> _class, int n) {
        arr = (T[]) Array.newInstance(_class, n);
        modCount = new long[n];
        Arrays.fill(modCount, masterModCount);
    }

    public T get(int index) {
        return modCount[index] >= masterModCount
                ? arr[index]
                : null;
    }

    public T put(int index, T value) {
        T result = get(index);
        arr[index] = value;

        modCount[index] = masterModCount;
        modified = true;

        return result;
    }

    public void clearAll() {
        if (modified) {
            masterModCount++;
            modified = false;
        }
    }
}