diff --git a/u07-1/PrimeTester.java b/u07-1/PrimeTester.java
new file mode 100644
index 0000000..95eafd8
--- /dev/null
+++ b/u07-1/PrimeTester.java
@@ -0,0 +1,63 @@
+import java.util.Random;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+
+class PrimeTester {
+	public static void main(String[] args) throws InterruptedException {
+		final AtomicInteger primeCount = new AtomicInteger();
+		final Random random = new Random();
+		ExecutorService executor = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());
+
+		for (int i = 0; i < 100; i++) {
+			final int start;
+			final int end;
+
+			if (i == 0) { // only start at 2
+				start = 2;
+			} else {
+				start = i * 100;
+			}
+
+			if (i == 99) { // end at 100.000 instead of 99.999
+				end = 100_001;
+			} else {
+				end = (i + 1) * 100;
+			}
+
+			Runnable t = () -> {
+				System.out.println("Testing " + start + " to " + (end - 1));
+				for (int j = start; j < end; j++) {
+					if (isPrime(j)) {
+						primeCount.incrementAndGet();
+					}
+					if (j == start / end) {
+						try {
+							Thread.sleep(random.nextInt(0, 100));
+						} catch (InterruptedException e) {
+							System.out.println("Thread interrupted: " + e.getMessage());
+							return;
+						}
+					}
+				}
+			};
+			executor.execute(t);
+		}
+
+		executor.shutdown();
+		executor.awaitTermination(10, TimeUnit.SECONDS);
+		System.out.println("Total prime numbers: " + primeCount.get());
+	}
+
+	private static boolean isPrime(int n) {
+		if (n < 2) return false;
+		if (n == 2) return true;
+		for (int d = 2; d < n; d++) {
+			if (n % d == 0) {
+				return false;
+			}
+		}
+		return true;
+	}
+}
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