Simple implementation of StopWatch

src/main/util/StopWatch.java

@@ -0,0 +1,39 @@
+package main.util;
+
+import java.time.Duration;
+
+public class StopWatch {
+    private long startMillis;
+    private long pauseMillis;
+    private boolean paused;
+
+    private StopWatch(long startMillis) {
+        this.startMillis = startMillis;
+        this.paused = false;
+    }
+
+    public static StopWatch start() {
+        return new StopWatch(System.currentTimeMillis());
+    }
+
+    public void pauseWatch() {
+        this.paused = true;
+        this.pauseMillis = System.currentTimeMillis();
+    }
+
+    public void continueWatch() {
+        if (this.paused) {
+            long currentMillis = System.currentTimeMillis();
+            this.startMillis += currentMillis - this.pauseMillis;
+            this.paused = false;
+        }
+    }
+
+    public Duration stop() {
+        if (this.paused) {
+            return Duration.ofMillis(this.pauseMillis - this.startMillis);
+        } else {
+            return Duration.ofMillis(System.currentTimeMillis() - this.startMillis);
+        }
+    }
+}

test/main/util/StopWatchTest.java

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+package main.util;
+
+import org.junit.Test;
+
+import java.time.Duration;
+import java.util.concurrent.locks.LockSupport;
+
+import static org.junit.Assert.assertEquals;
+
+public class StopWatchTest {
+    @Test
+    public void test_stopwatch() {
+        StopWatch stopWatch = StopWatch.start();
+        LockSupport.parkNanos(Duration.ofMillis(100).toNanos());
+        assertEquals(stopWatch.stop().toMillis() - 100, 0, 5);
+    }
+
+    @Test
+    public void test_pause() {
+        StopWatch stopWatch = StopWatch.start();
+        LockSupport.parkNanos(Duration.ofMillis(100).toNanos());
+        stopWatch.pauseWatch();
+        LockSupport.parkNanos(Duration.ofMillis(50).toNanos()); // does not matter as the watch is paused
+        assertEquals(stopWatch.stop().toMillis() - 100, 0, 5);
+    }
+
+    @Test
+    public void test_pause_continue() {
+        StopWatch stopWatch = StopWatch.start();
+        LockSupport.parkNanos(Duration.ofMillis(100).toNanos()); // run
+        stopWatch.pauseWatch();
+        LockSupport.parkNanos(Duration.ofMillis(50).toNanos()); // pause for this much time
+        stopWatch.continueWatch();
+        LockSupport.parkNanos(Duration.ofMillis(25).toNanos()); // again run for this much time
+        assertEquals(stopWatch.stop().toMillis() - (100 + 25), 0, 5);
+    }
+
+    @Test
+    public void test_pause_continue_pause() {
+        StopWatch stopWatch = StopWatch.start();
+        LockSupport.parkNanos(Duration.ofMillis(100).toNanos()); // run
+
+        stopWatch.pauseWatch();
+        LockSupport.parkNanos(Duration.ofMillis(50).toNanos()); // pause for this much time
+
+        stopWatch.continueWatch();
+        LockSupport.parkNanos(Duration.ofMillis(25).toNanos()); // again run for this much time
+
+        stopWatch.pauseWatch();
+        LockSupport.parkNanos(Duration.ofMillis(75).toNanos()); // pause
+
+        assertEquals(stopWatch.stop().toMillis() - (100 + 25), 0, 5);
+    }
+
+    @Test
+    public void test_pause_continue_pause_continue() {
+        StopWatch stopWatch = StopWatch.start();
+        LockSupport.parkNanos(Duration.ofMillis(100).toNanos()); // run
+
+        stopWatch.pauseWatch();
+        LockSupport.parkNanos(Duration.ofMillis(50).toNanos()); // pause for this much time
+
+        stopWatch.continueWatch();
+        LockSupport.parkNanos(Duration.ofMillis(25).toNanos()); // again run for this much time
+
+        stopWatch.pauseWatch();
+        LockSupport.parkNanos(Duration.ofMillis(75).toNanos()); // pause
+
+        stopWatch.continueWatch();
+        LockSupport.parkNanos(Duration.ofMillis(111).toNanos()); // again run for this much time
+
+        assertEquals(stopWatch.stop().toMillis() - (100 + 25 + 111), 0, 5);
+    }
+}