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...
This method is similar to {@link #map(Function)}, * but the provided mapper is one whose result is already an {@code Optional}, * and if invoked, {@code flatMap} does not wrap it with an additional * {@code Optional}. * * @param <U> The type parameter to the {@code Optional...
* 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...
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 ...
java.util.Optional是一个Java JDK8引入的类,借鉴了Google Guava工具包的Optional类,其目的是为了避免空指针问题(java.lang.NullPointerException)。 Optional是一个容器类,它可以存放空值或非空值对象,通过函数式方法进行判断、过滤和映射等操作,对空值进行处理并返回Optional对象。 二、实例方法 1、empty empty,直接...
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 ...
在JDK8之前,一个方法能接受的参数都是变量,例如:object.method(Object o),那么,如果需要传入一个动作呢?比如回调。那么你可能会想到匿名内部类。例如: 首先定义一个业务类: 代码语言:javascript 代码运行次数:0 运行 AI代码解释 publicclassPerson{publicvoidcreate(String name,PersonCallback personCallback){System...
Methods inherited from class java.lang.Object clone,finalize,getClass,notify,notifyAll,wait,wait,wait Method Detail empty public static <T>Optional<T> empty() Returns an emptyOptionalinstance. No value is present for this Optional. API Note: ...
Thefilter()method takes aPredicateas the argument. If a value is present in theOptionalobject and matches the predicate, thefilter()returns that value; otherwise, it returns an emptyOptionalobject. 5. How does anOptionalwork? If we open the source code ofOptional.java, we will find that va...
1.1.Java 9 中的增强 如果存在值,则此新方法将执行给定的Consumer操作,否则运行给定的Runnable操作。下面的代码先使用Java 8的的Stream流过滤3的倍数,然后通过findFirst找到第一个3的倍数。如果找到一个这样的值,就print控制台打印出来;如果没找到一个这样的值,就输出"没有找到3的倍数" ifPresentOrElse(Consumer,Run...