第10章示例代码

Author: ipofss

src/main/java/com/wbs/java8lambda/chapter10/Car.java

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+package com.wbs.java8lambda.chapter10;
+
+import java.util.Optional;
+
+/**
+ * TODO
+ *
+ * @author: wangbingshuai
+ * @create: 2019-11-09 14:40
+ **/
+public class Car {
+    private Optional<Insurance> insurance;
+
+    public Optional<Insurance> getInsurance() {
+        return insurance;
+    }
+}

src/main/java/com/wbs/java8lambda/chapter10/Insurance.java

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+package com.wbs.java8lambda.chapter10;
+
+/**
+ * TODO
+ *
+ * @author: wangbingshuai
+ * @create: 2019-11-09 14:39
+ **/
+public class Insurance {
+    private String name;
+
+    public String getName() {
+        return name;
+    }
+}

src/main/java/com/wbs/java8lambda/chapter10/Person.java

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+package com.wbs.java8lambda.chapter10;
+
+import java.util.Optional;
+
+/**
+ * TODO
+ *
+ * @author: wangbingshuai
+ * @create: 2019-11-09 14:42
+ **/
+public class Person {
+    private Optional<Car> car;
+
+    public Optional<Car> getCar() {
+        return car;
+    }
+}

src/main/java/com/wbs/java8lambda/chapter10/ReadPositiveIntParam.java

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+package com.wbs.java8lambda.chapter10;
+
+import java.util.Optional;
+import java.util.Properties;
+
+/**
+ * TODO
+ *
+ * @author: wangbingshuai
+ * @create: 2019-11-09 14:55
+ **/
+public class ReadPositiveIntParam {
+
+    public static void main(String[] args) {
+        Properties props = new Properties();
+        props.setProperty("a", "5");
+        props.setProperty("b", "true");
+        props.setProperty("c", "-3");
+
+        System.out.println(readDurationImperative(props, "a"));
+        System.out.println(readDurationImperative(props, "b"));
+        System.out.println(readDurationImperative(props, "c"));
+        System.out.println(readDurationImperative(props, "d"));
+
+        System.out.println(readDurationWithOptional(props, "a"));
+        System.out.println(readDurationWithOptional(props, "b"));
+        System.out.println(readDurationWithOptional(props, "c"));
+        System.out.println(readDurationWithOptional(props, "d"));
+    }
+
+    private 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;
+    }
+
+    private static int readDurationWithOptional(Properties props, String name) {
+        return Optional.ofNullable(props.getProperty(name))
+                .flatMap(ReadPositiveIntParam::s2i)
+                .filter(i -> i > 0).orElse(0);
+    }
+
+    private static Optional<Integer> s2i(String s) {
+        try {
+            return Optional.of(Integer.parseInt(s));
+        } catch (NumberFormatException e) {
+            return Optional.empty();
+        }
+    }
+}