[LANG-1332] ImmutableTriple.nullTriple()

src/changes/changes.xml

@@ -91,6 +91,7 @@ The <action> type attribute can be add,update,fix,remove.
     <action issue="LANG-1272" type="add" dev="ebourg">Add shuffle methods to ArrayUtils</action>
     <action issue="LANG-1317" type="add" dev="pschumacher" due-to="Yasser Zamani">Add MethodUtils#findAnnotation and extend MethodUtils#getMethodsWithAnnotation for non-public, super-class and interface methods</action>
     <action issue="LANG-1331" type="add" dev="ggregory">Add ImmutablePair.nullPair()</action>    
+    <action issue="LANG-1332" type="add" dev="ggregory">Add ImmutableTriple.nullTriple()</action>    
   </release>
 
   <release version="3.5" date="2016-10-13" description="New features including Java 9 detection">

src/main/java/org/apache/commons/lang3/tuple/ImmutableTriple.java

@@ -34,9 +34,27 @@
  */
 public final class ImmutableTriple<L, M, R> extends Triple<L, M, R> {
 
+    /**
+     * An immutable triple of nulls.
+     */
+    // This is not defined with generics to avoid warnings in call sites.
+    @SuppressWarnings("rawtypes")
+    private static final ImmutableTriple NULL = ImmutableTriple.of(null, null, null);
+
     /** Serialization version */
     private static final long serialVersionUID = 1L;
 
+    /** 
+     * Returns an immutable triple of nulls.
+     * 
+     * @return an immutable triple of nulls. 
+     * @since 3.6
+     */
+    @SuppressWarnings("unchecked")
+    public static <L, M, R> ImmutableTriple<L, M, R> nullTriple() {
+        return NULL;
+    }
+    
     /** Left object */
     public final L left;
     /** Middle object */

src/test/java/org/apache/commons/lang3/tuple/ImmutableTripleTest.java

@@ -18,7 +18,9 @@
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
 
 import java.io.ByteArrayInputStream;
@@ -85,6 +87,39 @@ public void testHashCode() throws Exception {
         assertEquals(ImmutableTriple.of(null, "foo", Boolean.TRUE).hashCode(), ImmutableTriple.of(null, "foo", Boolean.TRUE).hashCode());
     }
 
+    @Test
+    public void testNullTripleEquals() {
+        assertEquals(ImmutableTriple.nullTriple(), ImmutableTriple.nullTriple());
+    }
+        
+    @Test
+    public void testNullTripleSame() {
+        assertSame(ImmutableTriple.nullTriple(), ImmutableTriple.nullTriple());
+    }
+        
+    @Test
+    public void testNullTripleLeft() {
+        assertNull(ImmutableTriple.nullTriple().getLeft());
+    }
+        
+    @Test
+    public void testNullTripleMiddle() {
+        assertNull(ImmutableTriple.nullTriple().getMiddle());
+    }
+                
+    @Test
+    public void testNullTripleRight() {
+        assertNull(ImmutableTriple.nullTriple().getRight());
+    }
+        
+    @Test
+    public void testNullTripleTyped() {
+        // No compiler warnings
+        // How do we assert that?
+        ImmutableTriple<String, String, String> triple = ImmutableTriple.nullTriple();
+        assertNotNull(triple);
+    }
+
     @Test
     public void testToString() throws Exception {
         assertEquals("(null,null,null)", ImmutableTriple.of(null, null, null).toString());