Use isEmpty().

src/main/java/org/apache/commons/collections4/bag/TransformedBag.java

@@ -77,7 +77,7 @@ public class TransformedBag<E> extends TransformedCollection<E> implements Bag<E
      */
     public static <E> Bag<E> transformedBag(final Bag<E> bag, final Transformer<? super E, ? extends E> transformer) {
         final TransformedBag<E> decorated = new TransformedBag<>(bag, transformer);
-        if (bag.size() > 0) {
+        if (!bag.isEmpty()) {
             @SuppressWarnings("unchecked") // Bag is of type E
             final E[] values = (E[]) bag.toArray(); // NOPMD - false positive for generics
             bag.clear();

src/main/java/org/apache/commons/collections4/bag/TransformedSortedBag.java

@@ -78,7 +78,7 @@ public class TransformedSortedBag<E> extends TransformedBag<E> implements Sorted
             final Transformer<? super E, ? extends E> transformer) {
 
         final TransformedSortedBag<E>  decorated = new TransformedSortedBag<>(bag, transformer);
-        if (bag.size() > 0) {
+        if (!bag.isEmpty()) {
             @SuppressWarnings("unchecked") // bag is type E
             final E[] values = (E[]) bag.toArray(); // NOPMD - false positive for generics
             bag.clear();

src/main/java/org/apache/commons/collections4/collection/TransformedCollection.java

@@ -85,7 +85,7 @@ public class TransformedCollection<E> extends AbstractCollectionDecorator<E> {
 
         final TransformedCollection<E> decorated = new TransformedCollection<>(collection, transformer);
         // null collection & transformer are disallowed by the constructor call above
-        if (collection.size() > 0) {
+        if (!collection.isEmpty()) {
             @SuppressWarnings("unchecked") // collection is of type E
             final E[] values = (E[]) collection.toArray(); // NOPMD - false positive for generics
             collection.clear();

src/main/java/org/apache/commons/collections4/iterators/LoopingIterator.java

@@ -67,7 +67,7 @@ public class LoopingIterator<E> implements ResettableIterator<E> {
      */
     @Override
     public boolean hasNext() {
-        return collection.size() > 0;
+        return !collection.isEmpty();
     }
 
     /**

src/main/java/org/apache/commons/collections4/list/CursorableLinkedList.java

@@ -254,7 +254,7 @@ public class CursorableLinkedList<E> extends AbstractLinkedList<E> implements Se
      */
     @Override
     protected void removeAllNodes() {
-        if (size() > 0) {
+        if (!isEmpty()) {
             // superclass implementation would break all the iterators
             final Iterator<E> it = iterator();
             while (it.hasNext()) {

src/main/java/org/apache/commons/collections4/list/TransformedList.java

@@ -80,7 +80,7 @@ public class TransformedList<E> extends TransformedCollection<E> implements List
     public static <E> TransformedList<E> transformedList(final List<E> list,
                                                          final Transformer<? super E, ? extends E> transformer) {
         final TransformedList<E> decorated = new TransformedList<>(list, transformer);
-        if (list.size() > 0) {
+        if (!list.isEmpty()) {
             @SuppressWarnings("unchecked") // list is of type E
             final E[] values = (E[]) list.toArray(); // NOPMD - false positive for generics
             list.clear();

src/main/java/org/apache/commons/collections4/map/MultiKeyMap.java

@@ -105,10 +105,10 @@ public class MultiKeyMap<K, V> extends AbstractMapDecorator<MultiKey<? extends K
      */
     public static <K, V> MultiKeyMap<K, V> multiKeyMap(final AbstractHashedMap<MultiKey<? extends K>, V> map) {
         Objects.requireNonNull(map, "map");
-        if (map.size() > 0) {
-            throw new IllegalArgumentException("Map must be empty");
+        if (map.isEmpty()) {
+            return new MultiKeyMap<>(map);
         }
-        return new MultiKeyMap<>(map);
+        throw new IllegalArgumentException("Map must be empty");
     }
 
     //-----------------------------------------------------------------------

src/main/java/org/apache/commons/collections4/map/MultiValueMap.java

@@ -269,7 +269,7 @@ public class MultiValueMap<K, V> extends AbstractMapDecorator<K, Object> impleme
         if (coll == null) {
             coll = createCollection(1);  // might produce a non-empty collection
             coll.add((V) value);
-            if (coll.size() > 0) {
+            if (!coll.isEmpty()) {
                 // only add if non-zero size to maintain class state
                 decorated().put(key, coll);
                 result = true;  // map definitely changed
@@ -391,7 +391,7 @@ public class MultiValueMap<K, V> extends AbstractMapDecorator<K, Object> impleme
         if (coll == null) {
             coll = createCollection(values.size());  // might produce a non-empty collection
             coll.addAll(values);
-            if (coll.size() > 0) {
+            if (!coll.isEmpty()) {
                 // only add if non-zero size to maintain class state
                 decorated().put(key, coll);
                 result = true;  // map definitely changed

src/main/java/org/apache/commons/collections4/map/StaticBucketMap.java

@@ -511,7 +511,7 @@ public final class StaticBucketMap<K, V> extends AbstractIterableMap<K, V> {
         private Map.Entry<K, V> last;
 
         public boolean hasNext() {
-            if (current.size() > 0) {
+            if (!current.isEmpty()) {
                 return true;
             }
             while (bucket < buckets.length) {
@@ -522,7 +522,7 @@ public final class StaticBucketMap<K, V> extends AbstractIterableMap<K, V> {
                         n = n.next;
                     }
                     bucket++;
-                    if (current.size() > 0) {
+                    if (!current.isEmpty()) {
                         return true;
                     }
                 }

src/main/java/org/apache/commons/collections4/map/TransformedMap.java

@@ -104,7 +104,7 @@ public class TransformedMap<K, V>
             final Transformer<? super K, ? extends K> keyTransformer,
             final Transformer<? super V, ? extends V> valueTransformer) {
         final TransformedMap<K, V> decorated = new TransformedMap<>(map, keyTransformer, valueTransformer);
-        if (map.size() > 0) {
+        if (!map.isEmpty()) {
             final Map<K, V> transformed = decorated.transformMap(map);
             decorated.clear();
             decorated.decorated().putAll(transformed);  // avoids double transformation

src/main/java/org/apache/commons/collections4/map/TransformedSortedMap.java

@@ -96,7 +96,7 @@ public class TransformedSortedMap<K, V>
 
         final TransformedSortedMap<K, V> decorated =
                 new TransformedSortedMap<>(map, keyTransformer, valueTransformer);
-        if (map.size() > 0) {
+        if (!map.isEmpty()) {
             final Map<K, V> transformed = decorated.transformMap(map);
             decorated.clear();
             decorated.decorated().putAll(transformed);  // avoids double transformation

src/main/java/org/apache/commons/collections4/queue/TransformedQueue.java

@@ -75,7 +75,7 @@ public class TransformedQueue<E> extends TransformedCollection<E> implements Que
                                                            final Transformer<? super E, ? extends E> transformer) {
         // throws IAE if queue or transformer is null
         final TransformedQueue<E> decorated = new TransformedQueue<>(queue, transformer);
-        if (queue.size() > 0) {
+        if (!queue.isEmpty()) {
             @SuppressWarnings("unchecked") // queue is type <E>
             final E[] values = (E[]) queue.toArray(); // NOPMD - false positive for generics
             queue.clear();

src/main/java/org/apache/commons/collections4/set/CompositeSet.java

@@ -376,13 +376,13 @@ public class CompositeSet<E> implements Set<E>, Serializable {
         if (set != null) {
             for (final Set<E> existingSet : getSets()) {
                 final Collection<E> intersects = CollectionUtils.intersection(existingSet, set);
-                if (intersects.size() > 0) {
+                if (!intersects.isEmpty()) {
                     if (this.mutator == null) {
                         throw new UnsupportedOperationException(
                                 "Collision adding composited set with no SetMutator set");
                     }
                     getMutator().resolveCollision(this, existingSet, set, intersects);
-                    if (CollectionUtils.intersection(existingSet, set).size() > 0) {
+                    if (!CollectionUtils.intersection(existingSet, set).isEmpty()) {
                         throw new IllegalArgumentException(
                                 "Attempt to add illegal entry unresolved by SetMutator.resolveCollision()");
                     }

src/main/java/org/apache/commons/collections4/set/ListOrderedSet.java

@@ -82,7 +82,7 @@ public class ListOrderedSet<E>
     public static <E> ListOrderedSet<E> listOrderedSet(final Set<E> set, final List<E> list) {
         Objects.requireNonNull(set, "set");
         Objects.requireNonNull(list, "list");
-        if (set.size() > 0 || list.size() > 0) {
+        if (!set.isEmpty() || !list.isEmpty()) {
             throw new IllegalArgumentException("Set and List must be empty");
         }
         return new ListOrderedSet<>(set, list);

src/main/java/org/apache/commons/collections4/set/TransformedNavigableSet.java

@@ -74,7 +74,7 @@ public class TransformedNavigableSet<E> extends TransformedSortedSet<E> implemen
             final Transformer<? super E, ? extends E> transformer) {
 
         final TransformedNavigableSet<E> decorated = new TransformedNavigableSet<>(set, transformer);
-        if (set.size() > 0) {
+        if (!set.isEmpty()) {
             @SuppressWarnings("unchecked") // set is type E
             final E[] values = (E[]) set.toArray(); // NOPMD - false positive for generics
             set.clear();

src/main/java/org/apache/commons/collections4/set/TransformedSet.java

@@ -77,7 +77,7 @@ public class TransformedSet<E> extends TransformedCollection<E> implements Set<E
      */
     public static <E> Set<E> transformedSet(final Set<E> set, final Transformer<? super E, ? extends E> transformer) {
         final TransformedSet<E> decorated = new TransformedSet<>(set, transformer);
-        if (set.size() > 0) {
+        if (!set.isEmpty()) {
             @SuppressWarnings("unchecked") // set is type E
             final E[] values = (E[]) set.toArray(); // NOPMD - false positive for generics
             set.clear();

src/main/java/org/apache/commons/collections4/set/TransformedSortedSet.java

@@ -79,7 +79,7 @@ public class TransformedSortedSet<E> extends TransformedSet<E> implements Sorted
             final Transformer<? super E, ? extends E> transformer) {
 
         final TransformedSortedSet<E> decorated = new TransformedSortedSet<>(set, transformer);
-        if (set.size() > 0) {
+        if (!set.isEmpty()) {
             @SuppressWarnings("unchecked") // set is type E
             final E[] values = (E[]) set.toArray(); // NOPMD - false positive for generics
             set.clear();

src/test/java/org/apache/commons/collections4/bag/AbstractSortedBagTest.java

@@ -57,7 +57,7 @@ public abstract class AbstractSortedBagTest<T> extends AbstractBagTest<T> {
             }
             assertEquals("Element appears to be out of order.", last, confiter.next());
         }
-        if (getCollection().size() > 0) {
+        if (!getCollection().isEmpty()) {
             assertEquals("Incorrect element returned by first().", first,
                 getCollection().first());
             assertEquals("Incorrect element returned by last().", last,

src/test/java/org/apache/commons/collections4/collection/AbstractCollectionTest.java

@@ -1050,7 +1050,7 @@ public abstract class AbstractCollectionTest<E> extends AbstractObjectTest {
         assertEquals("Size of new Collection is 0.", 0, getCollection().size());
 
         resetFull();
-        assertTrue("Size of full collection should be greater than zero", getCollection().size() > 0);
+        assertFalse("Size of full collection should be greater than zero", getCollection().isEmpty());
     }
 
     /**

src/test/java/org/apache/commons/collections4/map/AbstractMapTest.java

@@ -1033,8 +1033,8 @@ public abstract class AbstractMapTest<K, V> extends AbstractObjectTest {
         // clear values, reflected in map
         resetFull();
         Collection<V> values = getMap().values();
-        assertTrue(getMap().size() > 0);
-        assertTrue(values.size() > 0);
+        assertFalse(getMap().isEmpty());
+        assertFalse(values.isEmpty());
         values.clear();
         assertTrue(getMap().isEmpty());
         assertTrue(values.isEmpty());
@@ -1042,8 +1042,8 @@ public abstract class AbstractMapTest<K, V> extends AbstractObjectTest {
         // clear map, reflected in values
         resetFull();
         values = getMap().values();
-        assertTrue(getMap().size() > 0);
-        assertTrue(values.size() > 0);
+        assertFalse(getMap().isEmpty());
+        assertFalse(values.isEmpty());
         getMap().clear();
         assertTrue(getMap().isEmpty());
         assertTrue(values.isEmpty());
@@ -1061,8 +1061,8 @@ public abstract class AbstractMapTest<K, V> extends AbstractObjectTest {
         // clear values, reflected in map
         resetFull();
         Set<K> keySet = getMap().keySet();
-        assertTrue(getMap().size() > 0);
-        assertTrue(keySet.size() > 0);
+        assertFalse(getMap().isEmpty());
+        assertFalse(keySet.isEmpty());
         keySet.clear();
         assertTrue(getMap().isEmpty());
         assertTrue(keySet.isEmpty());
@@ -1070,8 +1070,8 @@ public abstract class AbstractMapTest<K, V> extends AbstractObjectTest {
         // clear map, reflected in values
         resetFull();
         keySet = getMap().keySet();
-        assertTrue(getMap().size() > 0);
-        assertTrue(keySet.size() > 0);
+        assertFalse(getMap().isEmpty());
+        assertFalse(keySet.isEmpty());
         getMap().clear();
         assertTrue(getMap().isEmpty());
         assertTrue(keySet.isEmpty());
@@ -1089,8 +1089,8 @@ public abstract class AbstractMapTest<K, V> extends AbstractObjectTest {
         // clear values, reflected in map
         resetFull();
         Set<Map.Entry<K, V>> entrySet = getMap().entrySet();
-        assertTrue(getMap().size() > 0);
-        assertTrue(entrySet.size() > 0);
+        assertFalse(getMap().isEmpty());
+        assertFalse(entrySet.isEmpty());
         entrySet.clear();
         assertTrue(getMap().isEmpty());
         assertTrue(entrySet.isEmpty());
@@ -1098,8 +1098,8 @@ public abstract class AbstractMapTest<K, V> extends AbstractObjectTest {
         // clear map, reflected in values
         resetFull();
         entrySet = getMap().entrySet();
-        assertTrue(getMap().size() > 0);
-        assertTrue(entrySet.size() > 0);
+        assertFalse(getMap().isEmpty());
+        assertFalse(entrySet.isEmpty());
         getMap().clear();
         assertTrue(getMap().isEmpty());
         assertTrue(entrySet.isEmpty());

src/test/java/org/apache/commons/collections4/set/AbstractSortedSetTest.java

@@ -43,7 +43,6 @@ public abstract class AbstractSortedSetTest<E> extends AbstractSetTest<E> {
         super(name);
     }
 
-    //-----------------------------------------------------------------------
     /**
      * Verification extension, will check the order of elements,
      * the sets should already be verified equal.
@@ -67,7 +66,7 @@ public abstract class AbstractSortedSetTest<E> extends AbstractSetTest<E> {
             }
             assertEquals("Element appears to be out of order.", last, confiter.next());
         }
-        if (getCollection().size() > 0) {
+        if (!getCollection().isEmpty()) {
             assertEquals("Incorrect element returned by first().", first,
                 getCollection().first());
             assertEquals("Incorrect element returned by last().", last,
@@ -75,7 +74,6 @@ public abstract class AbstractSortedSetTest<E> extends AbstractSetTest<E> {
         }
     }
 
-    //-----------------------------------------------------------------------
     /**
      * Overridden because SortedSets don't allow null elements (normally).
      * @return false
@@ -99,7 +97,6 @@ public abstract class AbstractSortedSetTest<E> extends AbstractSetTest<E> {
         return (SortedSet<E>) super.makeFullCollection();
     }
 
-    //-----------------------------------------------------------------------
     /**
      * Returns an empty {@link TreeSet} for use in modification testing.
      *
@@ -110,9 +107,6 @@ public abstract class AbstractSortedSetTest<E> extends AbstractSetTest<E> {
         return new TreeSet<>();
     }
 
-    //-----------------------------------------------------------------------
-
-    //-----------------------------------------------------------------------
     /**
      * Override to return comparable objects.
      */