September 2017 Update

Task/Active-object/Java/active-object.java

@@ -0,0 +1,70 @@
+/**
+ * Integrates input function K over time
+ * S + (t1 - t0) * (K(t1) + K(t0)) / 2
+ */
+public class Integrator {
+
+    public interface Function {
+        double apply(double timeSinceStartInSeconds);
+    }
+
+    private final long start;
+    private volatile boolean running;
+
+    private Function func;
+    private double t0;
+    private double v0;
+    private double sum;
+
+    public Integrator(Function func) {
+        this.start = System.nanoTime();
+        setFunc(func);
+        new Thread(this::integrate).start();
+    }
+
+    public void setFunc(Function func) {
+        this.func = func;
+        v0 = func.apply(0.0);
+        t0 = 0;
+    }
+
+    public double getOutput() {
+        return sum;
+    }
+
+    public void stop() {
+        running = false;
+    }
+
+    private void integrate() {
+        running = true;
+        while (running) {
+            try {
+                Thread.sleep(1);
+                update();
+            } catch (InterruptedException e) {
+                return;
+            }
+        }
+    }
+
+    private void update() {
+        double t1 = (System.nanoTime() - start) / 1.0e9;
+        double v1 = func.apply(t1);
+        double rect = (t1 - t0) * (v0 + v1) / 2;
+        this.sum += rect;
+        t0 = t1;
+        v0 = v1;
+    }
+
+    public static void main(String[] args) throws InterruptedException {
+        Integrator integrator = new Integrator(t -> Math.sin(Math.PI * t));
+        Thread.sleep(2000);
+
+        integrator.setFunc(t -> 0.0);
+        Thread.sleep(500);
+
+        integrator.stop();
+        System.out.println(integrator.getOutput());
+    }
+}