optional examples (#2537)

guest/core-java-9/pom.xml

@@ -0,0 +1,27 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>com.stackify</groupId>
+  <artifactId>core-java-9</artifactId>
+  <version>0.0.1-SNAPSHOT</version>
+  
+  <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.12</version>
+        </dependency>
+    </dependencies>
+  
+  <build>
+    <plugins>
+      <plugin>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <version>3.6.2</version>
+        <configuration>
+          <source>1.9</source>
+          <target>1.9</target>
+        </configuration>
+      </plugin>
+    </plugins>
+  </build>
+</project>

guest/core-java-9/src/main/java/com/stackify/optional/User.java

@@ -0,0 +1,28 @@
+package com.stackify.optional;
+
+public class User {
+    private String email;
+    private String password;
+
+    public User(String email, String password) {
+        super();
+        this.email = email;
+        this.password = password;
+    }
+
+    public String getEmail() {
+        return email;
+    }
+
+    public void setEmail(String email) {
+        this.email = email;
+    }
+
+    public String getPassword() {
+        return password;
+    }
+
+    public void setPassword(String password) {
+        this.password = password;
+    }
+}

guest/core-java-9/src/test/java/com/stackify/optional/OptionalTest.java

@@ -0,0 +1,41 @@
+package com.stackify.optional;
+
+import org.junit.Test;
+import java.util.Optional;
+import java.util.List;
+
+import static org.junit.Assert.*;
+import java.util.stream.Collectors;
+
+public class OptionalTest {
+    
+    private User user;
+    
+    @Test
+    public void whenEmptyOptional_thenGetValueFromOr() {
+        User result = Optional.ofNullable(user)
+                .or( () -> Optional.of(new User("default","1234"))).get();
+                 
+        assertEquals(result.getEmail(), "default");
+    }
+    
+    @Test
+    public void whenIfPresentOrElse_thenOk() {
+        Optional.ofNullable(user)
+              .ifPresentOrElse( u -> System.out.println("User is:" + u.getEmail()), () -> System.out.println("User not found"));
+    }
+
+    @Test
+    public void whenGetStream_thenOk() {
+        User user = new User("john@gmail.com", "1234");
+        List<String> emails = Optional.ofNullable(user)
+                .stream()
+                .filter(u -> u.getEmail() != null && u.getEmail().contains("@"))
+                .map( u -> u.getEmail())
+                .collect(Collectors.toList());
+   
+        assertTrue(emails.size() == 1);
+        assertEquals(emails.get(0), user.getEmail());
+    }
+
+}