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public class OptionalDemo {
public static void main(String[] args) {
Insurance pacificOcean = new Insurance("太平洋", 3456d);
Insurance life = new Insurance("人寿", 2456d);
Car bmw = new Car("BMW", 320000d, null);
Car audi = new Car("AUDI", 350000d, life);
User lucy = new User("Lucy", bmw);
User lily = new User("Lily", null);
// 1、Optional.of()只能接受非空值,
Optional o = Optional.of(null);
// 2、Lily如果没有车子,默认给她一个audi
Car car = Optional.ofNullable(lily.getCar()).orElse(audi);
System.out.println(car);
// Lucy有一辆BMW车子
car = Optional.ofNullable(lucy.getCar()).orElse(bmw);
System.out.println(car);
// 3、如果 Optional 中有值,则对该值调用 consumer.accept,否则什么也不做。
Optional car1 = Optional.ofNullable(lily.getCar());
if (car1.isPresent()) {
car1.ifPresent(item -> System.out.println(item.getInsurance()));
} else {
System.out.println("Lily没有车子");
}
car1 = Optional.ofNullable(lucy.getCar());
if (car1.isPresent()) {
car1.ifPresent(item -> System.out.println(item.getInsurance()));
} else {
System.out.println("Lucy没有车子");
}// 4、Lily如果没有车子,现在给她指定一辆别克
car = Optional.ofNullable(lily.getCar()).orElseGet(() -> new Car("BUICK", 230000d, pacificOcean));
System.out.println(car);
// 5、Lily没有车子,抱怨一下
car = Optional.ofNullable(lily.getCar()).orElseThrow(() -> new RuntimeException("别人都有车子,我没有车子"));
System.out.println(car);
// 6、如果当前 Optional 为 Optional.empty,则依旧返回 Optional.empty;否则返回一个新的 Optional
String temp = Optional.ofNullable(lucy).map(User::getCar).map(Car::getInsurance).map(Insurance::getCompany).orElse("没有保险");
System.out.println(temp);
// 7、flatMap 方法与 map 方法的区别在于,map 方法参数中的函数 mapper 输出的是值,然后 map 方法会使用 Optional.ofNullable 将其包装为 Optional
temp = Optional.ofNullable(lucy)
.flatMap(item -> Optional.ofNullable(item.getCar()))
.flatMap(item -> Optional.ofNullable(item.getInsurance()))
.flatMap(item -> Optional.ofNullable(item.getCompany()))
.orElse("我车都没得,哪里有保险");
System.out.println(temp);
}
}@Data
@AllArgsConstructor
class User {
private String name;
private Car car;
}@Data
@AllArgsConstructor
class Car {
private String brand;
private double price;
private Insurance insurance;
}@Data
@AllArgsConstructor
class Insurance {
private String company;
private double cost;
}
【Optional的简单使用】
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