java.util.Optional 是java8中引进的一个新的类,我们通过Optional类的源码可以看到,该方法的作用可以对可能缺失的值进行建模,而不是直接将null赋值给变量。 Optional类产生背景 作为java开发者,业务逻辑中需要经常检查对象是否为空,因此业务中会产生大量的if else 结构和判断对象是否为空的方法(已经有很多判断对象是否...
详情也可参考Method References或Java 8 Method Reference: How to Use it。 二、用法示例 为充分体现Optional类的“威力”,首先以组合方式定义Location和Person两个类。 Location类: publicclassLocation{privateString country;privateString city;publicLocation(String country, String city){this.country = country;thi...
private static String getName() { System.out.println("execute method getName..."); return "answer"; } } 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 程序运行结果 execute method getName... AnswerAIL AnswerAIL execute ...
* 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); * } * </blockquote> * * @param ...
The filter() method takes a Predicate as the argument. If a value is present in the Optional object and matches the predicate, the filter() returns that value; otherwise, it returns an empty Optional object. 5. How does an Optional work? If we open the source code of Optional.java, ...
If a value is present, apply the providedOptional-bearing mapping function to it, return that result, otherwise return an emptyOptional. This method is similar tomap(Function), but the provided mapper is one whose result is already anOptional, and if invoked,flatMapdoes not wrap it with an ...
* @see java.util.Optional#ofNullable(Object) */@TestpublicvoidtestCreate(){// create oneOptional<User>userOne=Optional.<User>ofNullable(newUser());// 获取create one中封装的对象if(userOne.isPresent()){Assert.assertNotNull(userOne.get());}} ...
.toList());//Optional::stream method will return a stream of either one//or zero element if data is present or not.List<String>filteredListJava9=list.stream().flatMap(Optional::stream).collect(Collectors.toList());System.out.println(filteredList);System.out.println(filteredListJava9);}}...
具体可以参考这个答案Optional无疑是一个糟糕的设计，更适合 Java 的演化方向应该是在 Java 8 时增强空...
if (name.isPresent()) { System.out.println(name.get());//输出javaHuang } emptyValue.isPresent()==false get 源码: /** * If a value is present in this {@code Optional}, returns the value, * otherwise throws {@code NoSuchElementException}. * * @return the non-null value held by ...