Just another update

Task/Accumulator-factory/Java/accumulator-factory-3.java

@@ -1,30 +1,15 @@
-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();
-    }
+import java.util.function.DoubleUnaryOperator;
 
-    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));
-    }
+public interface AccumulatorFactory {
+  public static DoubleUnaryOperator accumulator(double element) {
+    double[] sum = new double[] { element };
+    return value -> sum[0] += value;
+  }
+
+  public static void main(String... arguments) {
+    DoubleUnaryOperator x = accumulator(1d);
+    x.applyAsDouble(5d);
+    System.out.println(accumulator(3d));		
+    System.out.println(x.applyAsDouble(2.3));
+  }
 }

Task/Accumulator-factory/Java/accumulator-factory-4.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));
+    }
+}