Update Num interface to implement Serializable

CHANGELOG.md

@@ -47,6 +47,7 @@ Changelog for `ta4j`, roughly following [keepachangelog.com](http://keepachangel
 - **PreviousValueIndicator** returns `NaN` if the (n-th) previous value of an indicator does not exist, i.e. if the (n-th) previous is below the first available index. 
 - **EnterAndHoldReturnCriterion** fixes exception thrown when bar series was empty
 - **BaseBarSeries** fixed `UnsupportedOperationException` when creating a bar series that is based on an unmodifiable collection
+- **Num** implements Serializable
 
 ### Changed
 - **BarSeriesManager** consider finishIndex when running backtest

ta4j-core/src/main/java/org/ta4j/core/num/DecimalNum.java

@@ -49,6 +49,8 @@
  */
 public final class DecimalNum implements Num {
 
+    private static final long serialVersionUID = 387498017007756808L;
+
     private static final int DEFAULT_PRECISION = 32;
     private static final Logger log = LoggerFactory.getLogger(DecimalNum.class);
 

ta4j-core/src/main/java/org/ta4j/core/num/DoubleNum.java

@@ -35,6 +35,8 @@
  */
 public class DoubleNum implements Num {
 
+    private static final long serialVersionUID = -1373009487614026992L;
+
     public static final DoubleNum ZERO = DoubleNum.valueOf(0);
     private static final DoubleNum ONE = DoubleNum.valueOf(1);
     private static final DoubleNum HUNDRED = DoubleNum.valueOf(100);

ta4j-core/src/main/java/org/ta4j/core/num/NaN.java

@@ -45,6 +45,8 @@
  */
 public class NaN implements Num {
 
+    private static final long serialVersionUID = -7292533679302352359L;
+
     /** A static Not-a-Number instance. */
     public static final Num NaN = new NaN();
 

ta4j-core/src/main/java/org/ta4j/core/num/Num.java

@@ -23,6 +23,7 @@
  */
 package org.ta4j.core.num;
 
+import java.io.Serializable;
 import java.math.BigDecimal;
 import java.math.MathContext;
 import java.math.RoundingMode;
@@ -37,7 +38,7 @@
  * @see DoubleNum
  * @see DecimalNum
  */
-public interface Num extends Comparable<Num> {
+public interface Num extends Comparable<Num>, Serializable {
 
     /**
      * @return the Num of 0

ta4j-core/src/test/java/org/ta4j/core/num/NumTest.java

@@ -25,13 +25,18 @@
 
 import static junit.framework.TestCase.assertEquals;
 import static junit.framework.TestCase.assertFalse;
+import static org.junit.Assert.assertNotSame;
 import static org.junit.Assert.assertTrue;
 import static org.ta4j.core.TestUtils.assertNumEquals;
 import static org.ta4j.core.TestUtils.assertNumNotEquals;
 import static org.ta4j.core.num.NaN.NaN;
 
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
 import java.math.BigDecimal;
 import java.math.MathContext;
 import java.math.RoundingMode;
@@ -346,4 +351,29 @@ public void sqrtOddExponent() {
         assertNumEquals("547722.55750516611345696978280080", sqrt);
     }
 
+    @Test
+    public void testSerialization() throws Exception {
+        Num numVal = numFunction.apply(1.3);
+        serializeDeserialize(numVal);
+    }
+
+    private static void serializeDeserialize(Num o) throws IOException, ClassNotFoundException {
+        byte[] array;
+        try (var baos = new ByteArrayOutputStream()) {
+            try (var out = new ObjectOutputStream(baos)) {
+                out.writeObject(o);
+                array = baos.toByteArray();
+            }
+
+        }
+        try (var baos = new ByteArrayInputStream(array)) {
+            try (var out = new ObjectInputStream(baos)) {
+                var deserialized = (Num) out.readObject();
+                assertNotSame(o, deserialized);
+                assertEquals(deserialized.doubleValue(), o.doubleValue());
+            }
+
+        }
+    }
+
 }