- fixes #8

Author: brunovinicius

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

@@ -150,14 +150,55 @@ public T first(Predicate<T> predicate) {
         return where(predicate).first();
     }
 
+    @Override
+    public T firstOrNull() {
+        return firstOrDefault(null);
+    }
+
+    @Override
+    public T firstOrNull(Predicate<T> predicate) {
+        return firstOrDefault(predicate, null);
+    }
+
+    @Override
+    public T firstOrDefault(T defaultValue) {
+        Iterator<T> iterator = iterator();
+        return iterator.hasNext() ? iterator.next() : defaultValue;
+    }
+
+    @Override
+    public T firstOrDefault(Predicate<T> predicate, T defaultValue) {
+        return where(predicate).firstOrDefault(defaultValue);
+    }
+
     @Override
     public T last() {
-        return reverseIterator().next();
+        return reverse().first();
     }
 
     @Override
     public T last(Predicate<T> predicate) {
-        return where(predicate).last();
+        return reverse().first(predicate);
+    }
+
+    @Override
+    public T lastOrNull() {
+        return lastOrDefault(null);
+    }
+
+    @Override
+    public T lastOrNull(Predicate<T> predicate) {
+        return lastOrDefault(predicate, null);
+    }
+
+    @Override
+    public T lastOrDefault(T defaultValue) {
+        return reverse().firstOrDefault(defaultValue);
+    }
+
+    @Override
+    public T lastOrDefault(Predicate<T> predicate, T defaultValue) {
+        return reverse().firstOrDefault(predicate, defaultValue);
     }
 
     @Override
@@ -174,6 +215,32 @@ public T single(Predicate<T> predicate) throws MultipleElementsFoundException {
         return where(predicate).single();
     }
 
+    @Override
+    public T singleOrNull() {
+        return singleOrDefault(null);
+    }
+
+    @Override
+    public T singleOrNull(Predicate<T> predicate) {
+        return singleOrDefault(predicate, null);
+    }
+
+    @Override
+    public T singleOrDefault(T defaultValue) {
+        Iterator<T> iterator = iterator();
+        if (!iterator.hasNext())
+            return defaultValue;
+        T result = iterator.next();
+        if (iterator.hasNext())
+            throw new MultipleElementsFoundException();
+        return result;
+    }
+
+    @Override
+    public T singleOrDefault(Predicate<T> predicate, T defaultValue) {
+        return where(predicate).singleOrDefault(defaultValue);
+    }
+
     @Override
     public List<T> toList() {
         List<T> list = new ArrayList<>();

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

@@ -6,6 +6,7 @@
 import java.math.BigDecimal;
 import java.util.List;
 import java.util.Map;
+import java.util.NoSuchElementException;
 
 /**
  * Decorates {@code Iterable<T>} objects to enable use of Linq like expressions.
@@ -225,48 +226,131 @@ public interface Stream<T> extends Iterable<T> {
     public int count();
 
     /**
-     * Returns the first element of a sequence.
+     * Returns the first element of a sequence; this method throws an exception if the sequence is empty.
      *
      * @return The first element in the specified sequence.
-     * @throws java.util.NoSuchElementException if the sequence is empty.
+     * @throws NoSuchElementException if the sequence is empty.
      */
     public T first();
 
     /**
-     * Returns the first element in a sequence that satisfies a specified condition.
+     * Returns the first element in a sequence that satisfies the specified condition; this method throws
+     * an exception if no element in the sequence satisfies the 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.
-     * @throws java.util.NoSuchElementException if no element matches the sequence.
+     * @throws NoSuchElementException if no element in the sequence satisfies the condition.
      */
     public T first(Predicate<T> predicate);
 
     /**
-     * Returns the last element of a sequence.
+     * Returns the first element of a sequence, or null if empty.
+     *
+     * @return The first element in the specified sequence, or null if empty.
+     */
+    public T firstOrNull();
+
+    /**
+     * Returns the first element in a sequence that satisfies a specified condition, or null if none does.
+     *
+     * @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.
+     */
+    public T firstOrNull(Predicate<T> predicate);
+
+    /**
+     * Returns the first element of a sequence, or defaultValue if empty.
+     *
+     * @return The first element in the specified sequence, or defaultValue if empty.
+     */
+    public T firstOrDefault(T defaultValue);
+
+    /**
+     * Returns the first element in a sequence that satisfies a specified condition, or defaultValue if none does.
+     *
+     * @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 or defaultValue if none does.
+     */
+    public T firstOrDefault(Predicate<T> predicate, T defaultValue);
+
+    /**
+     * Returns the last element of a sequence; this method throws an exception if the sequence is empty.
      *
      * @return The last element in the specified sequence.
-     * @throws java.util.NoSuchElementException if the sequence is empty.
+     * @throws NoSuchElementException if the sequence is empty.
      */
     public T last();
 
     /**
-     * Returns the last element in a sequence that satisfies a specified condition.
+     * Returns the last element in a sequence that satisfies the specified condition; this method throws
+     * an exception if no element in the sequence satisfies the 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.
+     * @throws NoSuchElementException if no element in the sequence satisfies the condition.
      */
     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.
+     * Returns the last element of a sequence, or null if empty.
+     *
+     * @return The last element in the specified sequence, or null if empty.
+     */
+    public T lastOrNull();
+
+    /**
+     * Returns the last element in a sequence that satisfies a specified condition, or null if none does.
+     *
+     * @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, or null if none does.
+     */
+    public T lastOrNull(Predicate<T> predicate);
+
+    /**
+     * Returns the last element of a sequence, or defaultValue if empty.
+     *
+     * @return The last element in the specified sequence, or defaultValue if empty.
+     */
+    public T lastOrDefault(T defaultValue);
+
+    /**
+     * Returns the last element in a sequence that satisfies a specified condition, or defaultValue if none does.
+     *
+     * @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, or or defaultValue if none does.
+     */
+    public T lastOrDefault(Predicate<T> predicate, T defaultValue);
+
+    /**
+     * Returns the only element of a sequence; this method throws an exception if there is more than
+     * one element in the sequence or if the sequence is empty.
      *
      * @return The single element of the input sequence, or default(TSource) if the sequence contains no elements.
      * @throws MultipleElementsFoundException The input sequence contains more than one matching element.
+     * @throws NoSuchElementException If the sequence is empty.
      */
     public T single() throws MultipleElementsFoundException;
 
+    /**
+     * Returns the only element of a sequence that satisfies a specified condition; this method throws an exception
+     * if multiple elements in the sequence satisfy the condition or if none does.
+     *
+     * @param predicate A function to test an element for a condition.
+     * @return The single element of the input sequence that satisfies the condition, or null if no such element is found.
+     * @throws MultipleElementsFoundException The input sequence contains more than one matching element.
+     * @throws NoSuchElementException If no element in the sequence satisfies the condition.
+     */
+    public T single(Predicate<T> predicate) throws MultipleElementsFoundException;
+
+    /**
+     * Returns the only element of a sequence, or a null if the sequence is empty; this method throws
+     * an exception if there is more than one element in the sequence.
+     *
+     * @return The single element of the input sequence, or default(TSource) if the sequence contains no elements.
+     * @throws MultipleElementsFoundException The input sequence contains more than one matching element.
+     */
+    public T singleOrNull();
+
     /**
      * Returns the only element of a sequence that satisfies a specified condition or null if
      * no such element exists; this method throws an exception if more than one element satisfies the condition.
@@ -275,7 +359,26 @@ public interface Stream<T> extends Iterable<T> {
      * @return The single element of the input sequence that satisfies the condition, or null if no such element is found.
      * @throws MultipleElementsFoundException The input sequence contains more than one matching element.
      */
-    public T single(Predicate<T> predicate) throws MultipleElementsFoundException;
+    public T singleOrNull(Predicate<T> predicate);
+
+    /**
+     * Returns the only element of a sequence, or a defaultValue if the sequence is empty; this method throws
+     * an exception if there is more than one element in the sequence.
+     *
+     * @return The single element of the input sequence, or default(TSource) if the sequence contains no elements.
+     * @throws MultipleElementsFoundException The input sequence contains more than one matching element.
+     */
+    public T singleOrDefault(T defaultValue);
+
+    /**
+     * Returns the only element of a sequence that satisfies a specified condition or defaultValue if
+     * no such element exists; this method throws an exception if more than one element satisfies the condition.
+     *
+     * @param predicate A function to test an element for a condition.
+     * @return The single element of the input sequence that satisfies the condition, or null if no such element is found.
+     * @throws MultipleElementsFoundException The input sequence contains more than one matching element.
+     */
+    public T singleOrDefault(Predicate<T> predicate, T defaultValue);
 
     /**
      * Creates a List from a Stream.

src/test/groovy/br/com/zbra/androidlinq/StreamTest.groovy

@@ -249,29 +249,61 @@ class StreamTest extends GroovyTestCase {
         shouldFail(NoSuchElementException.class, {
             assert stream(integers).first({ n -> n > 10 })
         })
+
+        // firstOrDefault
+        assert stream([]).firstOrDefault(10) == 10
+        assert stream(integers).firstOrDefault(10) == 0
+
+        // firstOrDefault passing Predicate
+        assert stream(integers).firstOrDefault({ n -> n > 5 }, 10) == 6
+        assert stream(integers).firstOrDefault({ n -> n == 100 }, -1) == -1
+
+        // firstOrNull
+        assert stream([]).firstOrNull() == null
+        assert stream(integers).firstOrNull() == 0
+
+        // firstOrDefault passing Predicate
+        assert stream(integers).firstOrNull({ n -> n > 5 }) == 6
+        assert stream(integers).firstOrNull({ n -> n == 100 }) == null
     }
 
     void testLast() {
         def integers = 0..9
 
-        // first with no parameters
+        // last with no parameters
         assert stream(integers).last() == 9
         shouldFail(NoSuchElementException.class, {
             assert stream([]).last()
         })
 
-        // first passing Predicate
+        // last passing Predicate
         assert stream(integers).last({ n -> n < 5 }) == 4
         shouldFail(NoSuchElementException.class, {
             assert stream(integers).last({ n -> n > 10 })
         })
+
+        // lastOrDefault
+        assert stream([]).lastOrDefault(10) == 10
+        assert stream(integers).lastOrDefault(10) == 9
+
+        // lastOrDefault passing Predicate
+        assert stream(integers).lastOrDefault({ n -> n < 5 }, 10) == 4
+        assert stream(integers).lastOrDefault({ n -> n == 100 }, -1) == -1
+
+        // lastOrNull
+        assert stream([]).lastOrNull() == null
+        assert stream(integers).lastOrNull() == 9
+
+        // lastOrDefault passing Predicate
+        assert stream(integers).lastOrNull({ n -> n < 5 }) == 4
+        assert stream(integers).lastOrNull({ n -> n == 100 }) == null
     }
 
     void testSingle() {
         def integers = 0..9
 
         // single with no parameters
-        assert  stream([5]).single() == 5
+        assert stream([5]).single() == 5
         shouldFail(NoSuchElementException.class, {
             stream([]).single()
         })
@@ -287,6 +319,34 @@ class StreamTest extends GroovyTestCase {
         shouldFail(MultipleElementsFoundException.class, {
             stream(integers).single({ n -> n > 5 })
         })
+
+        // singleOrDefault with no parameters
+        assert stream([5]).singleOrDefault(10) == 5
+        assert stream([]).singleOrDefault(10) == 10
+        shouldFail(MultipleElementsFoundException.class, {
+            stream(integers).singleOrDefault(10)
+        })
+
+        // singleOrDefault passing Predicate
+        assert stream(integers).singleOrDefault({ n -> n == 5 }, -1) == 5
+        assert stream(integers).singleOrDefault({ n -> n == 10 }, -1) == -1
+        shouldFail(MultipleElementsFoundException.class, {
+            stream(integers).singleOrDefault({ n -> n > 5 }, -1)
+        })
+
+        // singleOrNull with no parameters
+        assert stream([5]).singleOrNull() == 5
+        assert stream([]).singleOrNull() == null
+        shouldFail(MultipleElementsFoundException.class, {
+            stream(integers).singleOrNull()
+        })
+
+        // singleOrNull passing Predicate
+        assert stream(integers).singleOrNull({ n -> n == 5 }) == 5
+        assert stream(integers).singleOrNull({ n -> n == 10 }) == null
+        shouldFail(MultipleElementsFoundException.class, {
+            stream(integers).singleOrNull({ n -> n > 5 })
+        })
     }
 
     void testToList() {