optionalExample completed

src/test/java/option/OptionalExample.java

@@ -1,24 +1,30 @@
 package option;
 
+import org.junit.Before;
 import org.junit.Test;
 
 import java.util.Optional;
 import java.util.concurrent.ThreadLocalRandom;
 import java.util.function.Function;
+import java.util.function.Predicate;
+import java.util.function.Supplier;
 
+import static org.hamcrest.CoreMatchers.is;
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThat;
 
 public class OptionalExample {
 
+
     @Test
     public void get() {
         final Optional<String> o1 = Optional.empty();
 
-        o1.ifPresent(s -> System.out.println(s));
+        o1.ifPresent(System.out::println);
 
         o1.orElse("t");
         o1.orElseGet(() -> "t");
-        o1.orElseThrow(() -> new UnsupportedOperationException());
+//        o1.orElseThrow(UnsupportedOperationException::new);
     }
 
     @Test
@@ -50,6 +56,87 @@ public void map() {
         assertEquals(expected, actual);
     }
 
+    @Test
+    public void filter(){
+        final Optional<String> o1 = getOptional();
+
+        final Predicate<String> predicate = s -> s.equals("abc");
+        final Optional<String> expected = o1.filter(predicate);
+        final Optional<String> actual;
+
+        if(o1.isPresent()){
+            actual = predicate.test(o1.get()) ? o1 : Optional.empty();
+        }
+        else {
+            actual = Optional.empty();
+        }
+
+        assertThat(expected,is(actual));
+    }
+
+    @Test
+    public void flatMap(){
+        final Optional<String> o1 = getOptional();
+
+        final Optional<Integer> optional = o1.flatMap(s -> Optional.of(s.length()));
+
+        final Function<String, Optional<Integer>> function = s -> Optional.of(s.length());
+
+        final Optional<Integer> actual;
+
+        if(o1.isPresent()){
+            actual = function.apply(o1.get());
+        }
+        else {
+            actual = Optional.empty();
+        }
+
+        assertThat(optional,is(actual));
+    }
+
+    @Test
+    public void orElse(){
+        final Optional<String> o1 = getOptional();
+
+        final String actual = o1.orElse("defaultValue");
+
+        final String expected = o1.isPresent() ? o1.get() : "defaultValue";
+
+        assertThat(actual, is(expected));
+    }
+
+    @Test
+    public void orElseGet(){
+        final Optional<String> o1 = getOptional();
+
+        final Supplier<String> supplier = () -> "something";
+
+        final String actual = o1.orElseGet(() -> "something");
+
+        final String expected = o1.isPresent() ? o1.get() : supplier.get();
+
+        assertThat(actual,is(expected));
+    }
+
+    @Test
+    public void orElseThrow(){
+        final Optional<String> o1 = getOptional();
+
+        final String actual = o1.orElseThrow(() -> new RuntimeException("Error"));
+
+        Supplier<RuntimeException> exceptionSupplier =() -> new RuntimeException("Error");
+
+        final String expected;
+        if(o1.isPresent()){
+            expected = o1.get();
+        }
+        else {
+            throw exceptionSupplier.get();
+        }
+
+        assertThat(actual, is(expected));
+    }
+
     private Optional<String> getOptional() {
         return ThreadLocalRandom.current().nextBoolean()
             ? Optional.empty()