Optional task was done

src/test/java/option/OptionalExample.java

@@ -4,13 +4,40 @@
 
 import java.util.Optional;
 import java.util.concurrent.ThreadLocalRandom;
+import java.util.function.BiFunction;
 import java.util.function.Function;
 
 import static org.junit.Assert.assertEquals;
 
 public class OptionalExample {
 
+    public static <T1, T2, R> Optional<R> zipMap(Optional<T1> o1, Optional<T2> o2, BiFunction<T1, T2, R> function) {
+        return o1.flatMap(t1 ->
+                o2.map(t2 ->
+                   function.apply(t1, t2)));
+    }
+
     @Test
+    public void zipMap() {
+        final Optional<String> o1 = getOptional();
+        final Optional<String> o2 = getOptional();
+
+        BiFunction<String, String, Integer> function = (s1, s2) -> s1.length() + s2.length();
+
+        Optional<Integer> expected = zipMap(o1, o2, function);
+
+        Optional<Integer> actual;
+
+        if (o1.isPresent() && o2.isPresent()) {
+            actual = Optional.ofNullable(function.apply(o1.get(), o2.get()));
+        } else {
+            actual = Optional.empty();
+        }
+
+        assertEquals(expected, actual);
+    }
+
+    @Test(expected = UnsupportedOperationException.class)
     public void get() {
         final Optional<String> o1 = Optional.empty();
 
@@ -50,6 +77,83 @@ public void map() {
         assertEquals(expected, actual);
     }
 
+    @Test
+    public void flatMap() {
+        final Optional<String> strOptional = getOptional();
+
+        final Function<String, Optional<Integer>> getLength = s -> Optional.of(s.length());
+
+        final Optional<Integer> expected = strOptional.flatMap(getLength);
+
+        final Optional<Integer> actual;
+        if (strOptional.isPresent()) {
+            actual = getLength.apply(strOptional.get());
+        } else {
+            actual = Optional.empty();
+        }
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void orElseThrow() {
+        final Optional<String> strOptional = getOptional();
+
+        boolean expectedIsEmpty = false;
+        try {
+            strOptional.orElseThrow(() -> new RuntimeException());
+        } catch (RuntimeException e) {
+            expectedIsEmpty = true;
+        }
+
+        boolean actualIsEmpty = !strOptional.isPresent();
+
+        assertEquals(expectedIsEmpty, actualIsEmpty);
+    }
+
+    @Test
+    public void orElse() {
+        final Optional<String> strOptional = getOptional();
+
+        String expected = strOptional.orElse("test");
+
+        String actual;
+        if (strOptional.isPresent()) {
+            actual = "abc";
+        } else {
+            actual = "test";
+        }
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void orElseGet() {
+        final Optional<String> strOptional = getOptional();
+
+        String expected = strOptional.orElseGet(() -> "test");
+
+        String actual;
+        if (strOptional.isPresent()) {
+            actual = strOptional.get();
+        } else {
+            actual = "test";
+        }
+
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void filter() {
+        final Optional<String> strOptional = getOptional();
+
+        Optional<String> expected = strOptional.filter(t -> t.equals("abc"));
+
+        Optional<String> actual = strOptional;
+
+        assertEquals(expected, actual);
+    }
+
     private Optional<String> getOptional() {
         return ThreadLocalRandom.current().nextBoolean()
             ? Optional.empty()