OptionalTest

whatsmars-common/src/test/java/org/hongxi/java/Address.java

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+package org.hongxi.java;
+
+import lombok.Data;
+
+/**
+ * Created by shenhongxi on 2019/1/22.
+ */
+@Data
+public class Address {
+
+    private String province;
+
+    private String city;
+}

whatsmars-common/src/test/java/org/hongxi/java/User.java

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+package org.hongxi.java;
+
+import lombok.Data;
+
+/**
+ * Created by shenhongxi on 2019/1/22.
+ */
+@Data
+public class User {
+
+    private String name;
+
+    private Address address;
+}

whatsmars-common/src/test/java/org/hongxi/java/util/OptionalTest.java

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+package org.hongxi.java.util;
+
+import org.hongxi.java.Address;
+import org.hongxi.java.User;
+
+import java.util.Optional;
+
+/**
+ * Created by shenhongxi on 2019/1/22.
+ */
+public class OptionalTest {
+
+    public static void main(String[] args) {
+        Optional<String> emptyOpt = Optional.empty();
+        System.out.println(emptyOpt.isPresent());
+        System.out.println(emptyOpt.orElse("a"));
+        System.out.println(emptyOpt.isPresent());
+        System.out.println(emptyOpt.orElseGet(() -> {
+            String s1 = "a";
+            String s2 = "b";
+            return s1 + s2;
+        }));
+
+        String s = "Hello";
+        Optional<String> notNullOpt = Optional.of(s);
+        if (notNullOpt.isPresent()) {
+            System.out.println(notNullOpt.get());
+        }
+        notNullOpt = notNullOpt.filter(s1 -> s1.contains("xyz"));
+        System.out.println(notNullOpt.isPresent());
+    }
+
+    public static String getName(User user) {
+        return Optional.ofNullable(user)
+                .map(User::getName)
+                .orElse("Unknown");
+    }
+
+    public static String getCity(User user) throws IllegalArgumentException {
+        return Optional.ofNullable(user)
+                .map(User::getAddress)
+                .map(Address::getCity)
+                .orElseThrow(() -> new IllegalArgumentException("params cant not be null"));
+    }
+}