Merge pull request #717 from mP1/feature/Traversable-implements-CanBe…

…Empty

Traversable implements CanBeEmpty

src/main/java/walkingkooka/tree/Traversable.java

@@ -17,6 +17,7 @@
 
 package walkingkooka.tree;
 
+import walkingkooka.CanBeEmpty;
 import walkingkooka.Cast;
 
 import java.util.Iterator;
@@ -26,7 +27,7 @@
 /**
  * A {@link Traversable} is part of a tree holding branches and leaves all of which are traversables.
  */
-public interface Traversable<T extends Traversable<T>> {
+public interface Traversable<T extends Traversable<T>> extends CanBeEmpty {
 
     /**
      * Standard index response to indicate a unsuccessful scan of an item in a list.
@@ -156,4 +157,14 @@ default Optional<T> lastChild() {
     default Iterator<T> traversableIterator() {
         return TraversableIterator.with(Cast.to(this));
     }
+
+    // CanBeEmpty.......................................................................................................
+
+    /**
+     * Returns true if the children is empty
+     */
+    @Override
+    default boolean isEmpty() {
+        return this.children().isEmpty();
+    }
 }

src/main/java/walkingkooka/tree/TraversableTesting2.java

@@ -18,6 +18,7 @@
 package walkingkooka.tree;
 
 import org.junit.jupiter.api.Test;
+import walkingkooka.CanBeEmptyTesting;
 import walkingkooka.HashCodeEqualsDefinedTesting2;
 import walkingkooka.ToStringTesting;
 import walkingkooka.collect.list.Lists;
@@ -34,6 +35,7 @@
  */
 public interface TraversableTesting2<T extends Traversable<T>>
         extends BeanPropertiesTesting,
+        CanBeEmptyTesting<T>,
         HashCodeEqualsDefinedTesting2<T>,
         ToStringTesting<T>,
         TraversableTesting,