code.java

package experience;

import java.util.Timer;
import java.util.TimerTask;

/**
 * Count the API call in the last minute.
 * Created by siyao on 9/13/15.
 */
public class APICallCounter {
    private static APICallCounter API_CALL_COUNTER;
    private static final int PERIOD = 1000 * 10; // 10s
    private static final int SLIDES  = 10;
    private int ptr;
    private int count;
    private int[] buffer;
    private APICallCounter() {
        int interval = PERIOD / SLIDES;
        buffer = new int[SLIDES];
        ptr = 0;
        count = 0;
        TimerTask task = new TimerTask() {
            @Override
            public void run() {
                int ptr2 = (ptr + 1) % SLIDES;
                count -= buffer[ptr2];
                buffer[ptr2] = 0;
                ptr = ptr2;
                System.out.println("ptr->" + ptr);
            }
        };
        Timer timer = new Timer("timer");
        timer.scheduleAtFixedRate(task, interval, interval);
    }

    public static APICallCounter getInstance() {
        if (API_CALL_COUNTER == null) {
            return new APICallCounter();
        } else {
            return API_CALL_COUNTER;
        }
    }

    public int getCounting() {
        return count;
    }

    public void increase(int k) {
        buffer[ptr] += k;
        count += k;
    }

    public static void main(String[] args) {
        APICallCounter apiCallCounter = APICallCounter.getInstance();
        TimerTask timerTask = new TimerTask() {
            @Override
            public void run() {
                apiCallCounter.increase(10);
                System.out.println(apiCallCounter.getCounting());
            }
        };
        Timer timer = new Timer("test");
        timer.scheduleAtFixedRate(timerTask, 0, 1000);
    }
}