handle serialization of FractionField (which is a singleton) properly and test it

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@795909 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/commons/math/fraction/FractionField.java

@@ -31,8 +31,6 @@ import org.apache.commons.math.Field;
  * @since 2.0
  */
 public class FractionField implements Field<Fraction>, Serializable  {
-    // TODO: Add Serializable documentation
-    // TODO: Check Serializable implementation
 
     /** Serializable version identifier */
     private static final long serialVersionUID = -1257768487499119313L;
@@ -67,4 +65,12 @@ public class FractionField implements Field<Fraction>, Serializable  {
         private static final FractionField INSTANCE = new FractionField();
     }
 
+    /** Handle deserialization of the singleton.
+     * @return the singleton instance
+     */
+    private Object readResolve() {
+        // return the singleton instance
+        return LazyHolder.INSTANCE; 
+    }
+
 }

src/test/org/apache/commons/math/fraction/FractionFieldTest.java

@@ -0,0 +1,44 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.math.fraction;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import org.apache.commons.math.TestUtils;
+import org.junit.Test;
+
+public class FractionFieldTest {
+
+    @Test
+    public void testZero() {
+        assertEquals(Fraction.ZERO, FractionField.getInstance().getZero());
+    }
+
+    @Test
+    public void testOne() {
+        assertEquals(Fraction.ONE, FractionField.getInstance().getOne());
+    }
+
+    @Test
+    public void testSerial() {
+        // deserializing the singleton should give the singleton itself back
+        FractionField field = FractionField.getInstance();
+        assertTrue(field == TestUtils.serializeAndRecover(field));
+    }
+
+}