会抛空指针异常 Optional optional = Optional.of(null); System.out.println(optional); -- 输出结...
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 “no...
* * @apiNote A method reference to the exception constructor with an empty * argument list can be used as the supplier. For example, * {@code IllegalStateException::new} */ public <X extends Throwable> T orElseThrow(Supplier<? extends X> exceptionSupplier) throws X { if (value != ...
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...
Optional仅仅是一个功能:存放T类型的值或者null。它提供了一些有用的接口来避免显式的null检查,可以参考Java 8官方文档了解更多细节。 接下来看一点使用Optional的例子:可能为空的值或者某个类型的值: Optional<String>fullName=Optional.ofNullable(null); ...
execute method getName... answer execute method getName... answer 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 结果验证说明: 当 Optonal 的值是空值时, 无论 orElse 还是 orElseGet 都会执行; 而当返回的 Optional 有值时, orElse 会执行, 而 orElseGet 不会执行。 因此...
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, ...
原题: Understanding, Accepting and Leveraging Optional inJava 编者按:Java 9终于在9月21号发布,于是知乎上关于“现在Java初学用等Java9出来再学吗”之类的问题可能有更新。在 Java 8 引入Optional特性的基础上,Java 9 又为 Optional 类增加了三种方法:or()、ifPresentOrElse() 和 stream(),本文的最后,也针对...
This method supports post-processing on optional values, without the need to explicitly check for a return status. For example, the following code traverses a stream of file names, selects one that has not yet been processed, and then opens that file, returning anOptional<FileInputStream>: ...
8 public void optionalMethodDemo() { 9 Person person = new Person(); 10 Optional personOptional = Optional.of(person); 11 Optional 12 <optional> wrapper = personOptional.map(Person::getName); 13 Optional nameOptional = wrapper.orElseThrow(IllegalArgumentException::new); 14 String name1 = ...