就是几个简单的类，我在getter方法中打印了一些信息 ---staticclassGrandPa{privateFatherfather;publicFat...
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...
public class OptionalMapFilterDemo { public static void main(String[] args) { String pas...
* (return a default value if value not present) and * {@link #ifPresent(java.util.function.Consumer) ifPresent()} (execute a block * of code if the value is present). * * This is a value-based * class; use of identity-sensitive operations (including reference equality * ({@code =...
}classTest {publicstaticvoidmain(String[] args) {//使用——java8之前:用匿名类GreetingService greetService1 =newGreetingService() { @OverridepublicvoidsayMessage(String message) { System.out.println("匿名类:" +message); } }; greetService1.sayMessage("hello");//使用——java8及之后:可以用Lam...
首先需要解释,什么是identity-sensitive,可以参考object identity and equality in java identity-sensitive operations包含以下三种操作 reference equality,也就是== identity hash code synchronization Optional的JavaDoc中有这样一段描述 This is a value-based class; use of identity-sensitive operations (including refe...
* 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 ...
Java 8 最有趣的特性之一,就是引入了全新的 Optional 类。该类主要用来处理几乎每位程序员都碰到过的麻烦问题—— 空指针异常(NullPointerException)。 从本质上来说,该类属于包含可选值的封装类(wrapper class),因此它既可以包含对象也可以仅仅为空。
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...
Similarly, other functions defined inOptionalclass operate around the ‘value’ attribute only. Browse thesourcecode of Optional.javafor more insight. The defaultno-args constructor is definedprivate, so we can’t create an instance of Optional except for the 3 given ways in section 2. ...