Add all the A tasks

Task/Accumulator-factory/Java/accumulator-factory-1.java

@@ -0,0 +1,16 @@
+public class Accumulator {
+    private double sum;
+    public Accumulator(double sum0) {
+        sum = sum0;
+    }
+    public double call(double n) {
+        return sum += n;
+    }
+
+    public static void main(String[] args) {
+        Accumulator x = new Accumulator(1);
+        x.call(5);
+        System.out.println(new Accumulator(3));
+        System.out.println(x.call(2.3));
+    }
+}

Task/Accumulator-factory/Java/accumulator-factory-2.java

@@ -0,0 +1,19 @@
+import com.google.common.base.Function;
+
+public class AccumulatorFactory {
+	private static Function<Double, Double> accumulator(final Double elem) {
+		return new Function<Double, Double>() {
+			Double sum = elem;
+			@Override public Double apply(Double val) {
+				return sum += val;
+			}
+		};
+	}
+
+	public static void main(String[] args) {
+		Function<Double, Double> x = accumulator(1d);
+		x.apply(5d);
+		System.out.println(accumulator(3d));		
+		System.out.println(x.apply(2.3));
+	}
+}

Task/Accumulator-factory/Java/accumulator-factory-3.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));
+    }
+}