SlidingWindowMap - File two

package com.malagasys.slidingwindow;

import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

public class SlidingWindowMap {
    private final Map<String, SlidingWindow> map = new HashMap<>();

    public SlidingWindowMap(Set<String> keys, int maxCount, long periodMs) {
        //Just create a sliding window per key.
        for (String key : keys) {
            map.put(key, new SlidingWindow(periodMs, maxCount));
        }
    }

    public String getNextKey() {
        String nextKey = null;
        long currentTime = System.currentTimeMillis();

        for (Map.Entry<String, SlidingWindow> e : map.entrySet()) {
            //Slide the window to match current timestamp
            e.getValue().slideTo(currentTime);

            //If the window is not full yet, accept the key as the next key
            if (!e.getValue().isFull()) {
                e.getValue().logcall(currentTime);
                nextKey = e.getKey();
                break;
            }
        }

        return nextKey;
    }

    //========= Run ============
    public static void main(String[] args) throws Exception {
        Set<String> keys = new HashSet<>(Arrays.asList("key_a", "key_b", "key_c", "key_d"));
        SlidingWindowMap map = new SlidingWindowMap(keys, 5, 30000);

        for (int i = 0; i < 40; i++) {
            System.out.println(map.getNextKey());
            if (i%3 == 0) {
                Thread.sleep(5000);
            }
        }
    }
}