- added skip() and last() fixes #15 (tests pending)

Author: brunovinicius

src/main/java/br/com/zbra/androidlinq/AbstractStream.java

@@ -11,7 +11,11 @@
 
 abstract class AbstractStream<T> implements Stream<T> {
 
-    protected abstract Iterator<T> reverseIterator();
+    protected Iterator<T> reverseIterator() {
+        Deque<T> deque = new LinkedList<>();
+        for (T t : this) deque.addFirst(t);
+        return deque.iterator();
+    }
 
     @Override
     public Stream<T> where(Predicate<T> predicate) {
@@ -75,6 +79,11 @@ public Stream<T> take(int count) {
         return new TakeStream<>(this, count);
     }
 
+    @Override
+    public Stream<T> skip(int count) {
+        return new SkipStream<>(this, count);
+    }
+
     @Override
     public Stream<T> distinct() {
         HashSet<T> set = new HashSet<>();
@@ -133,29 +142,30 @@ public int count() {
 
     @Override
     public T first() {
-        Iterator<T> iterator = iterator();
-        if (iterator.hasNext())
-            return iterator.next();
-        return null;
+        return iterator().next();
     }
 
     @Override
     public T first(Predicate<T> predicate) {
-        for (T entry : this) {
-            if (predicate.apply(entry))
-                return entry;
-        }
-        return null;
+        return where(predicate).first();
+    }
+
+    @Override
+    public T last() {
+        return reverseIterator().next();
+    }
+
+    @Override
+    public T last(Predicate<T> predicate) {
+        return where(predicate).last();
     }
 
     @Override
     public T single() throws MultipleElementsFoundException {
-        T result = null;
-        for (T entry : this) {
-            if (result != null)
-                throw new MultipleElementsFoundException();
-            result = entry;
-        }
+        Iterator<T> iterator = iterator();
+        T result = iterator.next();
+        if (iterator.hasNext())
+            throw new MultipleElementsFoundException();
         return result;
     }
 

src/main/java/br/com/zbra/androidlinq/GroupByStream.java

@@ -24,7 +24,7 @@ public Iterator<Grouping<TKey, TElement>> iterator() {
 
     @Override
     protected Iterator<Grouping<TKey, TElement>> reverseIterator() {
-        return getGroupingIterator(stream.reverseIterator());
+        return super.reverseIterator();
     }
 
     private Iterator<Grouping<TKey, TElement>> getGroupingIterator(Iterator<T> iterator) {

src/main/java/br/com/zbra/androidlinq/IterableStream.java

@@ -16,12 +16,4 @@ public IterableStream(Iterable<T> iterable) {
     public Iterator<T> iterator() {
         return iterable.iterator();
     }
-
-    @Override
-    protected Iterator<T> reverseIterator() {
-        List<T> list = new ArrayList<>();
-        for (T t : iterable)
-            list.add(t);
-        return new ListStream.ReverseListIterator<>(list);
-    }
 }

src/main/java/br/com/zbra/androidlinq/ListStream.java

@@ -4,6 +4,7 @@
 import java.util.List;
 import java.util.ListIterator;
 
+
 class ListStream<T> extends AbstractStream<T> {
 
     private List<T> source;
@@ -26,19 +27,4 @@ public Iterator<T> iterator() {
     protected Iterator<T> reverseIterator() {
         return new ReverseListIterator<>(source);
     }
-
-    static class ReverseListIterator<T> implements Iterator<T> {
-        ListIterator<T> iterator;
-        public ReverseListIterator(List<T> list) {
-            iterator = list.listIterator(list.size());
-        }
-
-        public boolean hasNext() {
-            return iterator.hasPrevious();
-        }
-
-        public T next() {
-            return iterator.previous();
-        }
-    }
 }

src/main/java/br/com/zbra/androidlinq/MapStream.java

@@ -3,6 +3,7 @@
 import java.util.Iterator;
 import java.util.LinkedList;
 import java.util.Map;
+import java.util.SortedSet;
 
 public class MapStream<K, V> extends AbstractStream<Map.Entry<K, V>> {
 
@@ -24,7 +25,7 @@ public Iterator<Map.Entry<K, V>> iterator() {
 
     @Override
     protected Iterator<Map.Entry<K, V>> reverseIterator() {
-        return new LinkedList<>(map.entrySet()).descendingIterator();
+        return iterator();
     }
 
 }

src/main/java/br/com/zbra/androidlinq/ReverseListIterator.java

@@ -0,0 +1,21 @@
+package br.com.zbra.androidlinq;
+
+import java.util.Iterator;
+import java.util.List;
+import java.util.ListIterator;
+
+
+public class ReverseListIterator<T> implements Iterator<T> {
+    ListIterator<T> iterator;
+    public ReverseListIterator(List<T> list) {
+        iterator = list.listIterator(list.size());
+    }
+
+    public boolean hasNext() {
+        return iterator.hasPrevious();
+    }
+
+    public T next() {
+        return iterator.previous();
+    }
+}

src/main/java/br/com/zbra/androidlinq/SelectManyStream.java

@@ -22,7 +22,7 @@ public Iterator<TSelected> iterator() {
 
     @Override
     protected Iterator<TSelected> reverseIterator() {
-        return new SelectManyIterator<>(selector, stream.reverseIterator());
+        return super.reverseIterator();
     }
 
     private static class SelectManyIterator<T, TSelected> implements Iterator<TSelected> {

src/main/java/br/com/zbra/androidlinq/SkipStream.java

@@ -0,0 +1,54 @@
+package br.com.zbra.androidlinq;
+
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+class SkipStream<T> extends AbstractStream<T> {
+
+    private final int count;
+    private final AbstractStream<T> stream;
+
+    SkipStream(AbstractStream<T> stream, int count) {
+        this.stream = stream;
+        this.count = count;
+    }
+
+    @Override
+    public int count() {
+        int originalCount = stream.count();
+        return count >= originalCount ? 0 : originalCount - count;
+    }
+
+    @Override
+    public Iterator<T> iterator() {
+        return new SkipIterator<>(stream.iterator(), count);
+    }
+
+    @Override
+    protected Iterator<T> reverseIterator() {
+        return super.reverseIterator();
+    }
+
+    private static class SkipIterator<T> implements Iterator<T> {
+        private final long count;
+        private final Iterator<T> wrapped;
+
+        public SkipIterator(Iterator<T> wrapped, long count) {
+            this.count = count;
+            this.wrapped = wrapped;
+
+            for (int i = 0; i < count && wrapped.hasNext(); i++)
+                wrapped.next();
+        }
+
+        @Override
+        public boolean hasNext() {
+            return wrapped.hasNext();
+        }
+
+        @Override
+        public T next() {
+            return wrapped.next();
+        }
+    }
+}

src/main/java/br/com/zbra/androidlinq/Stream.java

@@ -124,6 +124,14 @@ public interface Stream<T> extends Iterable<T> {
      */
     public Stream<T> take(int count);
 
+    /**
+     * Skips a specified number of contiguous elements from the start of a sequence then returns remaining elements.
+     *
+     * @param count The number of elements to skip.
+     * @return An Stream of type T that contains the elements after the number of elements skipped from the start of the input sequence.
+     */
+    public Stream<T> skip(int count);
+
     /**
      * Returns distinct elements from a sequence by using the object {@code equals()} to compare values.
      *
@@ -219,18 +227,37 @@ public interface Stream<T> extends Iterable<T> {
     /**
      * Returns the first element of a sequence.
      *
-     * @return The first element in the specified sequence or null if the sequence is empty.
+     * @return The first element in the specified sequence.
+     * @throws java.util.NoSuchElementException if the sequence is empty.
      */
     public T first();
 
     /**
      * Returns the first element in a sequence that satisfies a specified condition.
      *
      * @param predicate A function to test each element for a condition.
-     * @return The first element in the sequence that passes the test in the specified predicate function or null if none does.
+     * @return The first element in the sequence that passes the test in the specified predicate function.
+     * @throws java.util.NoSuchElementException if no element matches the sequence.
      */
     public T first(Predicate<T> predicate);
 
+    /**
+     * Returns the last element of a sequence.
+     *
+     * @return The last element in the specified sequence.
+     * @throws java.util.NoSuchElementException if the sequence is empty.
+     */
+    public T last();
+
+    /**
+     * Returns the last element in a sequence that satisfies a specified condition.
+     *
+     * @param predicate A function to test each element for a condition.
+     * @return The last element in the sequence that passes the test in the specified predicate function.
+     * @throws java.util.NoSuchElementException if no element matches the sequence.
+     */
+    public T last(Predicate<T> predicate);
+
     /**
      * Returns the only element of a sequence, or a default value if the sequence is empty; this method throws
      * an exception if there is more than one element in the sequence.

src/main/java/br/com/zbra/androidlinq/TakeStream.java

@@ -11,28 +11,32 @@ class TakeStream<T> extends AbstractStream<T> {
     TakeStream(AbstractStream<T> stream, int count) {
         this.stream = stream;
 
-        if (count <= 0)
+        if (count < 0)
             throw new IllegalArgumentException("count must be greater than 0: " + count);
 
         this.count = count;
     }
 
+    @Override
+    public int count() {
+        return count == 0 ? 0 : Math.min(count, stream.count());
+    }
+
     @Override
     public Iterator<T> iterator() {
         return new TakeIterator<>(stream.iterator(), count);
     }
 
     @Override
     protected Iterator<T> reverseIterator() {
-        return new TakeIterator<>(stream.reverseIterator(), count);
+        return super.reverseIterator();
     }
 
     private static class TakeIterator<T> implements Iterator<T> {
+        private long index = 0;
         private final long count;
         private final Iterator<T> wrapped;
 
-        long index = 0;
-
         public TakeIterator(Iterator<T> wrapped,  long count) {
             this.count = count;
             this.wrapped = wrapped;