September 2017 Update

Task/Accumulator-factory/Java/accumulator-factory-5.java

@@ -0,0 +1,30 @@
+public class Accumulator {
+    private Long sumA; // non-null if we're working in the integer domain
+    private double sumB;
+    public Accumulator(Number sum0) {
+	if (sum0 instanceof Double) {
+	    sumB = sum0.doubleValue();
+	} else {
+	    sumA = sum0.longValue();
+	}
+    }
+    public Number call(Number n) {
+        if (sumA != null) {
+	    if (n instanceof Double) {
+		sumB = n.doubleValue() + sumA;
+		sumA = null;
+		return sumB;
+	    }
+            return sumA += n.longValue();
+        }
+        return sumB += n.doubleValue();
+    }
+
+    public static void main(String[] args) {
+        Accumulator x = new Accumulator(1);
+        x.call(5);
+        Accumulator y = new Accumulator(3);
+        System.out.println(y+" has value "+y.call(0));
+        System.out.println(x.call(2.3));
+    }
+}