Optional 是 Java 8 引进的一个新特性,我们通常认为Optional是用于缓解Java臭名昭著的空指针异常问题。 Brian Goetz (Java语言设计架构师)对Optional设计意图的原话如下: Optional is intended to provide a limited mechanism for library method return types where there needed to be a clear way to represent “...
publicstaticStringinWhichCityLowercaseTU(Person person){//Traditional&Uglyif(person !=null) {Locationlocation=person.getLocation();if(location !=null) {Stringcity=location.getCity();if(city !=null) {returncity.toLowerCase(); }else{return"nowhere"; } }else{return"nowhere"; } }else{return"no...
greetService1.sayMessage("hello");//使用——java8及之后:可以用Lambda表达式GreetingService greetService2 = message -> System.out.println("Lambda表达式:" +message); greetService2.sayMessage("helo"); } } Java8为函数式接口引入了一个新的注解@FunctionalInterface,主要用于编译级错误检查,加上该注解,...
* Checks that the specified object reference is not {@code null}. This * method is designed primarily for doing parameter validation in methods * and constructors, as demonstrated below: * <blockquote> * public Foo(Bar bar) { * this.bar = Objects.requireNonNull(bar); * } * </blockquo...
* Additional methods that depend on the presence or absence of a contained * value are provided, such as {@link #orElse(java.lang.Object) orElse()} * (return a default value if value not present) and * {@link #ifPresent(java.util.function.Consumer) ifPresent()} (execute a block ...
Java 8中推出了Optional<T>,专门来解决这一问题。我们先来看看官方文档的介绍。 A container object which may or may not contain a non-null value. If a value is present, isPresent() will return true and get() will return the value. Additional methods that depend on the presence or absence of...
java.lang.Object java.util.Optional<T> public final classOptional<T>extendsObject A container object which may or may not contain a non-null value. If a value is present,isPresent()will returntrueandget()will return the value. Additional methods that depend on the presence or absence of a...
Rule 4: It's generally a bad idea to create an Optional for the specific purpose of chaining methods from it to get a value. 链式语法可以让代码的处理流程看起来更加清晰,但是为了链式而去使用Optional的话,在某些情况下并不会显得有多优雅
This essentially means thatOptionalshould be used as the return type of certain service, repository or utility methods only where they truly serve the purpose. 9. Conclusion In this article, we learned how we can adopt the new Java SE 8java.util.Optional. The purpose ofOptionalis not to rep...
The Optional API is also rich and provides a couple of useful methods likeifPresent()andorElseThrow()which can be used to throw an Exception if the value is not present. You can further seeon Udemyto learn about Java API and the modern way of Java Coding. ...