[add] add Optional examples in Java 8 module.

brianway · brianway · commit dae9e1f4636b · 2017-03-27T20:23:27.000+08:00
diff --git a/java8/README.md b/java8/README.md
@@ -54,4 +54,13 @@
 - ChainOfResponsibilityMain: 责任链模式
 - FactoryMain: 工厂模式
 - Debugging: 查看栈跟踪
-- Peek: 使用日志调试
+- Peek: 使用日志调试
+- Ambiguous: 默认方法解决冲突
+
+
+Optional
+
+- Car,Insurance,Person: 模型类
+- OptionalMain: ptional 用法(map,flatMap,filter)
+- OptionalInAction:  使用 Optional 实战示例
+- ReadPositiveIntParam: 使用 Optional 示例
diff --git a/java8/pom.xml b/java8/pom.xml
@@ -11,4 +11,11 @@
 
     <artifactId>java8</artifactId>
 
+    <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+        </dependency>
+    </dependencies>
+
 </project>
diff --git a/java8/src/main/java/com/brianway/learning/java8/effective/Ambiguous.java b/java8/src/main/java/com/brianway/learning/java8/effective/Ambiguous.java
@@ -0,0 +1,30 @@
+package com.brianway.learning.java8.effective;
+
+/**
+ * 默认方法解决冲突
+ */
+public class Ambiguous {
+
+    public static void main(String... args) {
+        new C().hello();
+    }
+
+    interface A {
+        default void hello() {
+            System.out.println("Hello from A");
+        }
+    }
+
+    interface B {
+        default void hello() {
+            System.out.println("Hello from B");
+        }
+    }
+
+    static class C implements B, A {
+        public void hello() {
+            A.super.hello();// Java 8 引入的新语法: X.super.m(...)
+            // 其中 X 为希望调用 m 方法所在的父接口
+        }
+    }
+}
diff --git a/java8/src/main/java/com/brianway/learning/java8/effective/optional/Car.java b/java8/src/main/java/com/brianway/learning/java8/effective/optional/Car.java
@@ -0,0 +1,12 @@
+package com.brianway.learning.java8.effective.optional;
+
+import java.util.Optional;
+
+public class Car {
+
+    private Optional<Insurance> insurance;
+
+    public Optional<Insurance> getInsurance() {
+        return insurance;
+    }
+}
diff --git a/java8/src/main/java/com/brianway/learning/java8/effective/optional/Insurance.java b/java8/src/main/java/com/brianway/learning/java8/effective/optional/Insurance.java
@@ -0,0 +1,10 @@
+package com.brianway.learning.java8.effective.optional;
+
+public class Insurance {
+
+    private String name;
+
+    public String getName() {
+        return name;
+    }
+}
diff --git a/java8/src/main/java/com/brianway/learning/java8/effective/optional/OptionalInAction.java b/java8/src/main/java/com/brianway/learning/java8/effective/optional/OptionalInAction.java
@@ -0,0 +1,43 @@
+package com.brianway.learning.java8.effective.optional;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+/**
+ * Created by brian on 17/3/27.
+ * 使用 Optional 实战示例
+ */
+public class OptionalInAction {
+
+    private static Map<String, Object> map = new HashMap<>();
+
+    public static void main(String[] args) {
+        Optional<Object> value = getValue("key");
+        System.out.println(value.orElse("this is null"));
+
+        System.out.println(stringToInt("123"));
+        System.out.println(stringToInt("dd"));
+
+    }
+
+    /**
+     * 用 Optional 封装可能为 null 的值
+     */
+    public static Optional<Object> getValue(String key) {
+        Optional<Object> value = Optional.ofNullable(map.get(key));
+        return value;
+    }
+
+    /**
+     * 异常与 Optional 的对比
+     */
+    public static Optional<Integer> stringToInt(String s) {
+        try {
+            return Optional.of(Integer.parseInt(s));
+        } catch (NumberFormatException e) {
+            return Optional.empty();
+        }
+    }
+
+}
diff --git a/java8/src/main/java/com/brianway/learning/java8/effective/optional/OptionalMain.java b/java8/src/main/java/com/brianway/learning/java8/effective/optional/OptionalMain.java
@@ -0,0 +1,45 @@
+package com.brianway.learning.java8.effective.optional;
+
+import java.util.Optional;
+
+/**
+ * Optional 用法:
+ * - 使用 map 从 Optional 对象提取和转换值
+ * - 使用 flatMap 链接 Optional 对象
+ * - 两个 Optional 对象的组合
+ * - 使用 filter 剔除特定值
+ */
+public class OptionalMain {
+
+    public static void main(String[] args) {
+        Optional<Person> person = Optional.of(new Person());
+        //Optional<Person> person2 = Optional.empty();
+        String name = getCarInsuranceName(person);
+        System.out.println(name);
+    }
+
+    public static String getCarInsuranceName(Optional<Person> person) {
+        return person.flatMap(Person::getCar)
+                .flatMap(Car::getInsurance)
+                .map(Insurance::getName)
+                .orElse("Unknown");
+    }
+
+    public Insurance findCheapestInsurance(Person person, Car car) {
+        //省略业务逻辑
+        Insurance cheapestCompany = new Insurance();
+        return cheapestCompany;
+    }
+
+    public Optional<Insurance> nullSafeFindCheapestInsurance(Optional<Person> person, Optional<Car> car) {
+        return person.flatMap(
+                p -> car.map(
+                        c -> findCheapestInsurance(p, c)));
+    }
+
+    public void PrintIfWithName(String name) {
+        Optional<Insurance> optInsurance = Optional.of(new Insurance());
+        optInsurance.filter(insurance -> name.equals(insurance.getName()))
+                .ifPresent(x -> System.out.println("ok"));
+    }
+}
diff --git a/java8/src/main/java/com/brianway/learning/java8/effective/optional/Person.java b/java8/src/main/java/com/brianway/learning/java8/effective/optional/Person.java
@@ -0,0 +1,12 @@
+package com.brianway.learning.java8.effective.optional;
+
+import java.util.Optional;
+
+public class Person {
+
+    private Car car;
+
+    public Optional<Car> getCar() {
+        return Optional.ofNullable(car);
+    }
+}
diff --git a/java8/src/main/java/com/brianway/learning/java8/effective/optional/ReadPositiveIntParam.java b/java8/src/main/java/com/brianway/learning/java8/effective/optional/ReadPositiveIntParam.java
@@ -0,0 +1,44 @@
+package com.brianway.learning.java8.effective.optional;
+
+import static java.util.Optional.empty;
+import static java.util.Optional.of;
+import static java.util.Optional.ofNullable;
+
+import java.util.Optional;
+import java.util.Properties;
+
+/**
+ * 使用 Optional 示例
+ * test case 见 test 目录
+ */
+public class ReadPositiveIntParam {
+
+    public static int readDurationImperative(Properties props, String name) {
+        String value = props.getProperty(name);
+        if (value != null) {
+            try {
+                int i = Integer.parseInt(value);
+                if (i > 0) {
+                    return i;
+                }
+            } catch (NumberFormatException nfe) {
+            }
+        }
+        return 0;
+    }
+
+    public static int readDurationWithOptional(Properties props, String name) {
+        return ofNullable(props.getProperty(name))
+                .flatMap(ReadPositiveIntParam::s2i)
+                .filter(i -> i > 0).orElse(0);
+    }
+
+    public static Optional<Integer> s2i(String s) {
+        try {
+            return of(Integer.parseInt(s));
+        } catch (NumberFormatException e) {
+            return empty();
+        }
+    }
+
+}
diff --git a/java8/src/main/java/com/brianway/learning/java8/lambda/FilteringApples.java b/java8/src/main/java/com/brianway/learning/java8/lambda/FilteringApples.java
@@ -34,6 +34,7 @@ public static void main(String[] args) {
     /**
      * 根据抽象条件筛选
      * 将迭代集合的逻辑和要应用到集合中每个元素的行为区分开
+     *
      * @param inventory
      * @param p
      * @return
diff --git a/java8/src/main/java/com/brianway/learning/java8/streamapi/Laziness.java b/java8/src/main/java/com/brianway/learning/java8/streamapi/Laziness.java
@@ -15,7 +15,8 @@ public static void main(String[] args) {
         List<Integer> twoEvenSquares =
                 numbers.stream()
                         .filter(n -> {
-                            System.out.println("filtering " + n); return n % 2 == 0;
+                            System.out.println("filtering " + n);
+                            return n % 2 == 0;
                         })
                         .map(n -> {
                             System.out.println("mapping " + n);
diff --git a/java8/src/main/java/com/brianway/learning/java8/streamapi/usage/Filtering.java b/java8/src/main/java/com/brianway/learning/java8/streamapi/usage/Filtering.java
@@ -16,38 +16,38 @@
  */
 public class Filtering {
 
-    public static void main(String...args){
+    public static void main(String... args) {
 
         // Filtering with predicate
         List<Dish> vegetarianMenu =
-            menu.stream()
-                .filter(Dish::isVegetarian)
-                .collect(toList());
+                menu.stream()
+                        .filter(Dish::isVegetarian)
+                        .collect(toList());
 
         vegetarianMenu.forEach(System.out::println);
 
         // Filtering unique elements
         List<Integer> numbers = Arrays.asList(1, 2, 1, 3, 3, 2, 4);
         numbers.stream()
-               .filter(i -> i % 2 == 0)
-               .distinct()
-               .forEach(System.out::println);
+                .filter(i -> i % 2 == 0)
+                .distinct()
+                .forEach(System.out::println);
 
         // Truncating a stream
         List<Dish> dishesLimit3 =
-            menu.stream()
-                .filter(d -> d.getCalories() > 300)
-                .limit(3)
-                .collect(toList());
+                menu.stream()
+                        .filter(d -> d.getCalories() > 300)
+                        .limit(3)
+                        .collect(toList());
 
         dishesLimit3.forEach(System.out::println);
 
         // Skipping elements
         List<Dish> dishesSkip2 =
-            menu.stream()
-                .filter(d -> d.getCalories() > 300)
-                .skip(2)
-                .collect(toList());
+                menu.stream()
+                        .filter(d -> d.getCalories() > 300)
+                        .skip(2)
+                        .collect(toList());
 
         dishesSkip2.forEach(System.out::println);
     }
diff --git a/java8/src/main/java/com/brianway/learning/java8/streamapi/usage/Finding.java b/java8/src/main/java/com/brianway/learning/java8/streamapi/usage/Finding.java
@@ -10,32 +10,32 @@
  */
 public class Finding {
 
-    public static void main(String...args){
-        if(isVegetarianFriendlyMenu()){
+    public static void main(String... args) {
+        if (isVegetarianFriendlyMenu()) {
             System.out.println("Vegetarian friendly");
         }
 
         System.out.println(isHealthyMenu());
         System.out.println(isHealthyMenu2());
-        
+
         Optional<Dish> dish = findVegetarianDish();
         dish.ifPresent(d -> System.out.println(d.getName()));
     }
-    
-    private static boolean isVegetarianFriendlyMenu(){
+
+    private static boolean isVegetarianFriendlyMenu() {
         return menu.stream().anyMatch(Dish::isVegetarian);
     }
-    
-    private static boolean isHealthyMenu(){
+
+    private static boolean isHealthyMenu() {
         return menu.stream().allMatch(d -> d.getCalories() < 1000);
     }
-    
-    private static boolean isHealthyMenu2(){
+
+    private static boolean isHealthyMenu2() {
         return menu.stream().noneMatch(d -> d.getCalories() >= 1000);
     }
-    
-    private static Optional<Dish> findVegetarianDish(){
+
+    private static Optional<Dish> findVegetarianDish() {
         return menu.stream().filter(Dish::isVegetarian).findAny();
     }
-    
+
 }
diff --git a/java8/src/test/java/com/brianway/learning/java8/effective/optional/ReadPositiveIntParamTest.java b/java8/src/test/java/com/brianway/learning/java8/effective/optional/ReadPositiveIntParamTest.java
@@ -0,0 +1,32 @@
+package com.brianway.learning.java8.effective.optional;
+
+import static com.brianway.learning.java8.effective.optional.ReadPositiveIntParam.readDurationImperative;
+import static com.brianway.learning.java8.effective.optional.ReadPositiveIntParam.readDurationWithOptional;
+import static junit.framework.TestCase.assertEquals;
+import org.junit.Test;
+
+import java.util.Properties;
+
+/**
+ * Created by brian on 17/3/27.
+ */
+public class ReadPositiveIntParamTest {
+    @Test
+    public void testMap() {
+        Properties props = new Properties();
+        props.setProperty("a", "5");
+        props.setProperty("b", "true");
+        props.setProperty("c", "-3");
+
+        assertEquals(5, readDurationImperative(props, "a"));
+        assertEquals(0, readDurationImperative(props, "b"));
+        assertEquals(0, readDurationImperative(props, "c"));
+        assertEquals(0, readDurationImperative(props, "d"));
+
+        assertEquals(5, readDurationWithOptional(props, "a"));
+        assertEquals(0, readDurationWithOptional(props, "b"));
+        assertEquals(0, readDurationWithOptional(props, "c"));
+        assertEquals(0, readDurationWithOptional(props, "d"));
+    }
+
+}
