[LANG-1458] Add EMPTY_ARRAY constants to classes in

org.apache.commons.lang3.tuple

src/changes/changes.xml

@@ -47,7 +47,8 @@ The <action> type attribute can be add,update,fix,remove.
 
   <release version="3.10" date="YYYY-MM-DD" description="TBD">
     <action issue="LANG-1450" type="fix" dev="chtompki">Generate javadoc jar on build.</action>
-    <action issue="LANG-1457" type="fix" dev="ggregory">Add ExceptionUtils.throwableOfType(Throwable, Class) and friends.</action>
+    <action issue="LANG-1457" type="add" dev="ggregory">Add ExceptionUtils.throwableOfType(Throwable, Class) and friends.</action>
+    <action issue="LANG-1458" type="add" dev="ggregory">Add EMPTY_ARRAY constants to classes in org.apache.commons.lang3.tuple.</action>
   </release>
 
   <release version="3.9" date="2019-04-09" description="New features and bug fixes. Requires Java 8, supports Java 9, 10, 11">

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

@@ -33,6 +33,28 @@
  */
 public final class ImmutablePair<L, R> extends Pair<L, R> {
 
+    /**
+     * An empty array.
+     * <p>
+     * Consider using {@link #emptyArray()} to avoid generics warnings.
+     * </p>
+     *
+     * @since 3.10.
+     */
+    public static final ImmutablePair<?, ?>[] EMPTY_ARRAY = new ImmutablePair[0];
+
+    /**
+     * Returns the empty array singleton that can be assigned without compiler warning.
+     * 
+     * @return the empty array singleton that can be assigned without compiler warning.
+     *
+     * @since 3.10.
+     */
+    @SuppressWarnings("unchecked")
+    public static final <L, R> ImmutablePair<L, R>[] emptyArray() {
+        return (ImmutablePair<L, R>[]) EMPTY_ARRAY;
+    }
+
     /**
      * An immutable pair of nulls.
      */

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

@@ -34,6 +34,28 @@
  */
 public final class ImmutableTriple<L, M, R> extends Triple<L, M, R> {
 
+    /**
+     * An empty array.
+     * <p>
+     * Consider using {@link #emptyArray()} to avoid generics warnings.
+     * </p>
+     *
+     * @since 3.10.
+     */
+    public static final ImmutableTriple<?, ?, ?>[] EMPTY_ARRAY = new ImmutableTriple[0];
+
+    /**
+     * Returns the empty array singleton that can be assigned without compiler warning.
+     * 
+     * @return the empty array singleton that can be assigned without compiler warning.
+     *
+     * @since 3.10.
+     */
+    @SuppressWarnings("unchecked")
+    public static final <L, M, R> ImmutableTriple<L, M, R>[] emptyArray() {
+        return (ImmutableTriple<L, M, R>[]) EMPTY_ARRAY;
+    }
+
     /**
      * An immutable triple of nulls.
      */

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

@@ -28,6 +28,28 @@
  */
 public class MutablePair<L, R> extends Pair<L, R> {
 
+    /**
+     * An empty array.
+     * <p>
+     * Consider using {@link #emptyArray()} to avoid generics warnings.
+     * </p>
+     *
+     * @since 3.10.
+     */
+    public static final MutablePair<?, ?>[] EMPTY_ARRAY = new MutablePair[0];
+
+    /**
+     * Returns the empty array singleton that can be assigned without compiler warning.
+     * 
+     * @return the empty array singleton that can be assigned without compiler warning.
+     *
+     * @since 3.10.
+     */
+    @SuppressWarnings("unchecked")
+    public static final <L, R> MutablePair<L, R>[] emptyArray() {
+        return (MutablePair<L, R>[]) EMPTY_ARRAY;
+    }
+
     /** Serialization version */
     private static final long serialVersionUID = 4954918890077093841L;
 

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

@@ -29,6 +29,28 @@
  */
 public class MutableTriple<L, M, R> extends Triple<L, M, R> {
 
+    /**
+     * The empty array singleton.
+     * <p>
+     * Consider using {@link #emptyArray()} to avoid generics warnings.
+     * </p>
+     *
+     * @since 3.10.
+     */
+    public static final MutableTriple<?, ?, ?>[] EMPTY_ARRAY = new MutableTriple[0];
+    
+    /**
+     * Returns the empty array singleton that can be assigned without compiler warning.
+     * 
+     * @return the empty array singleton that can be assigned without compiler warning.
+     *
+     * @since 3.10.
+     */
+    @SuppressWarnings("unchecked")
+    public static final <L, M, R> MutableTriple<L, M, R>[] emptyArray() {
+        return (MutableTriple<L, M, R>[]) EMPTY_ARRAY;
+    }
+
     /** Serialization version */
     private static final long serialVersionUID = 1L;
 

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

@@ -39,6 +39,19 @@
  */
 public class ImmutablePairTest {
 
+    @Test
+    public void testEmptyArrayLength() {
+        @SuppressWarnings("unchecked")
+        final ImmutablePair<Integer, String>[] empty = (ImmutablePair<Integer, String>[]) ImmutablePair.EMPTY_ARRAY;
+        assertEquals(0, empty.length);
+    }
+    
+    @Test
+    public void testEmptyArrayGenerics() {
+        final ImmutablePair<Integer, String>[] empty = ImmutablePair.emptyArray();
+        assertEquals(0, empty.length);
+    }
+    
     @Test
     public void testBasic() {
         final ImmutablePair<Integer, String> pair = new ImmutablePair<>(0, "foo");

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

@@ -39,6 +39,19 @@
  */
 public class ImmutableTripleTest {
 
+    @Test
+    public void testEmptyArrayLength() {
+        @SuppressWarnings("unchecked")
+        final ImmutableTriple<Integer, String, Boolean>[] empty = (ImmutableTriple<Integer, String, Boolean>[]) ImmutableTriple.EMPTY_ARRAY;
+        assertEquals(0, empty.length);
+    }
+    
+    @Test
+    public void testEmptyArrayGenerics() {
+        final ImmutableTriple<Integer, String, Boolean>[] empty = ImmutableTriple.emptyArray();
+        assertEquals(0, empty.length);
+    }
+    
     @Test
     public void testBasic() {
         final ImmutableTriple<Integer, String, Boolean> triple = new ImmutableTriple<>(0, "foo", Boolean.TRUE);

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

@@ -32,6 +32,19 @@
  */
 public class MutablePairTest {
 
+    @Test
+    public void testEmptyArrayLength() {
+        @SuppressWarnings("unchecked")
+        final MutablePair<Integer, String>[] empty = (MutablePair<Integer, String>[]) MutablePair.EMPTY_ARRAY;
+        assertEquals(0, empty.length);
+    }
+    
+    @Test
+    public void testEmptyArrayGenerics() {
+        final MutablePair<Integer, String>[] empty = MutablePair.emptyArray();
+        assertEquals(0, empty.length);
+    }
+        
     @Test
     public void testBasic() {
         final MutablePair<Integer, String> pair = new MutablePair<>(0, "foo");

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

@@ -32,6 +32,19 @@
  */
 public class MutableTripleTest {
 
+    @Test
+    public void testEmptyArrayLength() {
+        @SuppressWarnings("unchecked")
+        final MutableTriple<Integer, String, Boolean>[] empty = (MutableTriple<Integer, String, Boolean>[]) MutableTriple.EMPTY_ARRAY;
+        assertEquals(0, empty.length);
+    }
+    
+    @Test
+    public void testEmptyArrayGenerics() {
+        final MutableTriple<Integer, String, Boolean>[] empty = MutableTriple.emptyArray();
+        assertEquals(0, empty.length);
+    }
+    
     @Test
     public void testBasic() {
         final MutableTriple<Integer, String, Boolean> triple = new MutableTriple<>(0, "foo", Boolean.FALSE);