SlidingTimeThreshold.java

public class SlidingTimeThreshold {
    
    private final long[] samples;
    private final long windowMillis;
    private int index;
    
    public SlidingTimeThreshold(final long window, final TimeUnit timeUnit, final int threshold) {
        this.windowMillis = timeUnit.toMillis(window);
        this.samples = new long[threshold];
    }
    
    public synchronized boolean update() {
        long currentTs = TimeSource.currentTimeMillis();
        samples[index] = currentTs;
        index = (index + 1) % samples.length;
        if (samples[index] <= currentTs - windowMillis) {
            return false;
        } else {
            return true;
        }
    }
}

public class SlidingTimeThresholdTest {
    
    private SlidingTimeThreshold slidingTimeThreshold;
    
    @Before
    public void setUp() throws Exception {
        slidingTimeThreshold = new SlidingTimeThreshold(1500, TimeUnit.MILLISECONDS, 20);
    }
    
    @Test
    public void testSlidingIterate() throws Exception {
        for (int i = 0; i < 30; i++) {
            assertFalse(slidingTimeThreshold.update());
            TimeSource.advance(2000);
        }
    }
    
    @Test
    public void testThreshold() throws Exception {
        for (int i = 0; i < 19; i++) {
            assertFalse(slidingTimeThreshold.update());
        }
        assertTrue(slidingTimeThreshold.update());
        TimeSource.advance(2000);
        assertFalse(slidingTimeThreshold.update());
    }
}