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enjoyCoding666enjoyCoding666
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java8的Optional
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6 files changed

+324
-61
lines changed

‎src/main/java/com/bean/Address.java‎

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package com.bean;
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import lombok.AllArgsConstructor;
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import lombok.Builder;
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import lombok.Data;
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import lombok.NoArgsConstructor;
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import java.util.Optional;
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/**
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* @Author: EnjoyCoding
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* @Date: 2020\3\6 0006 23:31
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* @Description:
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*/
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public class Address {
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private String country;
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private String province;
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private String city;
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public Address(String country, String province, String city) {
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this.country = country;
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this.province = province;
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this.city = city;
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}
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public Address() {
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}
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public String getCountry() {
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return country;
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}
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public void setCountry(String country) {
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this.country = country;
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}
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public String getProvince() {
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return province;
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}
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public void setProvince(String province) {
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this.province = province;
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}
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public void setCity(String city) {
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this.city = city;
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}
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public Optional<String> getCity() {
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return Optional.ofNullable(this.city);
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}
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}

‎src/main/java/com/bean/User.java‎

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package com.bean;
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import java.util.Optional;
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/**
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* Created by lenovo on 三月
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*/
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public class User {
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private String name;
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private String password;
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private String email;
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public User() {
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}
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public User(String name, String password, String email) {
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this.name = name;
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this.password = password;
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this.email = email;
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}
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public String getName() {
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return name;
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}
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public void setName(String name) {
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this.name = name;
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}
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public String getPassword() {
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return password;
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}
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public void setPassword(String password) {
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this.password = password;
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}
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public String getEmail() {
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return email;
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}
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public void setEmail(String email) {
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this.email = email;
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}
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@Override
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public String toString() {
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return "User{" +
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"name='" + name + '\'' +
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", password='" + password + '\'' +
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", email='" + email + '\'' +
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'}';
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}
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private String name;
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private String password;
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private String email;
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private Address address;
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public Optional<Address> getAddress() {
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return Optional.ofNullable(address);
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}
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public User() {
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}
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public User(String name, String password, String email) {
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this.name = name;
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this.password = password;
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this.email = email;
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}
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public String getName() {
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return name;
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}
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public void setName(String name) {
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this.name = name;
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}
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public String getPassword() {
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return password;
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}
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public void setPassword(String password) {
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this.password = password;
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}
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public String getEmail() {
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return email;
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}
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public void setEmail(String email) {
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this.email = email;
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}
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@Override
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public String toString() {
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return "User{" +
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"name='" + name + '\'' +
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", password='" + password + '\'' +
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", email='" + email + '\'' +
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'}';
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}
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}

‎src/main/java/com/bean/Worker.java‎

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package com.bean;
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import java.util.Optional;
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/**
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* @Author: EnjoyCoding
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* @Date: 2020\1\20 0020 20:42
@@ -12,12 +14,34 @@ public class Worker {
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private String name;
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private Address address;
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public Worker(String id, Integer age, String name) {
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this.id = id;
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this.age = age;
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this.name = name;
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}
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public Worker(String id, Integer age, String name, Address address) {
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this.id = id;
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this.age = age;
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this.name = name;
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this.address = address;
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}
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/**
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* 重写getAdress()方法，返回Optional对象。
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* @return
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*/
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public Optional<Address> getAdress() {
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return Optional.ofNullable(this.address);
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}
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public void setAddress(Address address) {
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this.address = address;
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}
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public String getId() {
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return id;
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}
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public void setName(String name) {
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this.name = name;
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}
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}

‎src/main/java/com/java8/lambda/LambdaForeach2.java‎

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This file was deleted.

‎src/main/java/com/java8/optional/OptionalDemo.java‎

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package com.java8.optional;
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import com.alibaba.fastjson.support.odps.udf.CodecCheck;
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import com.bean.Address;
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import com.bean.Worker;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.Optional;
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/**
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* @Author: EnjoyCoding
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* @Date: 2020\3\5 0005 23:28
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* @Description:
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*/
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public class OptionalDemo {
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/**
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* orElse(默认值)，如果Optional<T>封装的对象不存在值，则返回默认值。
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*/
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public static void orElseDemo() {
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// Worker worker1=new Worker("123",18,"lin");
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Worker worker1 = null;
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Worker worker2 = new Worker("456", 28, "chen");
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//如果worker1不为null，则orElse返回worker1,否则返回默认值worker2
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Worker result = Optional.ofNullable(worker1).orElse(worker2);
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//相当于以下代码：
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// if (worker1 != null) {
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// result = worker1;
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// } else {
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// result = worker2;
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// }
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System.out.println(result.getName() + "," + result.getAge());
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}
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/**
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* orElseGet()，如果Optional<T>封装的对象不存在值，则执行Supplier函数式。
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* orElseGet(Supplier<? extends T> other)，返回的类型必须和Optional封装的对象类型一致。
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*/
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public static void ofElseGetDemo() {
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String name1 = null;
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String name2 = "lin";
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//orElseGet(Supplier<? extends T> other)，返回的类型必须和Optional封装的对象类型一致。
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String result = Optional.ofNullable(name1).orElseGet(OptionalDemo::supplier);
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System.out.println(result);
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}
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public static String supplier() {
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return "orElseGet(Supplier)";
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}
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/**
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* of(对象)，如果封装的对象为空，则会报出空指针异常
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*/
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public static void ofDemo() {
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// Worker worker1=new Worker("123",18,"lin");
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Worker worker1 = null;
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Worker worker2 = new Worker("456", 28, "chen");
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Worker result = Optional.of(worker1).orElse(worker2);
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System.out.println(result.getName() + "," + result.getAge());
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}
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/**
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* isPresent()表示如果Optional<T>封装的对象不为空，就返回true。
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*/
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public static void isPresentDemo() {
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Worker worker1 = new Worker("123", 18, "lin");
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Optional<Worker> workerOpt = Optional.ofNullable(worker1);
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//这种写法比较丑，可以直接用下面的ifPresent()方法代替。
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boolean isPresent = workerOpt.isPresent();
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if (isPresent) {
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System.out.println(workerOpt.get().getName());
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}
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//以上代码，相当于：
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// if (worker1 != null) {
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// System.out.println(worker1.getName());
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// }
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}
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/**
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* ifPresent()表示如果对象不为null，则会执行对应的lambda语句。
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*/
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public static void ifPresentDemo() {
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// Address address=new Address("中国","广东","深圳");
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// Worker worker1=new Worker("123",18,"lin",address);
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Worker worker1 = new Worker("123", 18, "lin");
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// Worker worker1=null;
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List<String> nameList = new ArrayList<>();
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Optional.ofNullable(worker1).ifPresent(worker -> nameList.add(worker.getName()));
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//上面这句代码的作用相当于以下注释的代码：
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// if (worker1 != null) {
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// nameList.add(worker1.getName());
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// }
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nameList.forEach(System.out::println);
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}
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/**
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* 这种大量的判空代码很丑。
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*/
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public static void tooMuchNull(Worker worker) {
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// if (worker != null) {
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// Address address=worker.getAddress();
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// if (address != null) {
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// String city=address.getCity();
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// }
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// }
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}
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/**
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* flatMap()，如果Optional封装对象不为空，就会执行对应的mapping函数，返回Optional类型的值。
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* 否则就返回一个空的Optional对象。
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*/
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public static void flatMapDemo() {
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Address address = new Address("中国", "广东", "深圳");
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Worker worker = new Worker("123", 18, "lin", address);
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//默认值为"default"，有没有更好的选择？
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String city = Optional.ofNullable(worker)
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.flatMap(Worker::getAdress)
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.flatMap(Address::getCity)
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.orElse("default");
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System.out.println(city);
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}
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/**
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* orElseThrow(),如果Optional封装的对象为空，就会抛出对应的异常。
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*/
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public static void orElseThrowDemo() {
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// Worker worker = new Worker("123", 18, "lin");
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Worker worker = null;
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Worker result = Optional.ofNullable(worker)
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.orElseThrow(IllegalArgumentException::new);
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System.out.println(result.getName());
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}
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public static void filterDemo() {
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Worker worker = new Worker("123", 18, "lin");
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Optional<Worker> result = Optional.ofNullable(worker)
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.filter(worker1 -> worker1.getAge() > 20);
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//如果符合条件(比如，年龄大于20)则为true，不符合则为false
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System.out.println(result.isPresent());
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}
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}

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