Optional这个类最新是从 Java 8 中引入的,其主要目的如上面我们介绍的,就是为了解决 Java 中广受诟病的空异常。 Java 从 类型级别(type-level) 给出了一个解决方案,用来替代null。 In this tutorial, we’re going to show theOptionalclass that was introduced in Java 8. 如果你还想对 Java 的Optional了...
首先,重构类,使其 getter 方法返回Optional引用: publicclassUser{privateAddress address;publicOptional<Address>getAddress(){returnOptional.ofNullable(address); }// ...}publicclassAddress{privateCountry country;publicOptional<Country>getCountry(){returnOptional.ofNullable(country); }// ...} 上面的嵌套结构...
实例 importjava.util.Optional;importjava.util.function.Supplier;publicclassTester{publicstaticvoidmain(String[]args){Optional<String>optional1=Optional.of("Mahesh");Supplier<Optional<String>>supplierString=()->Optional.of("Not Present");optional1=optional1.or(supplierString);optional1.ifPresent(x->S...
@Test(expected=IllegalArgumentException.class)publicvoidwhenOrElseThrowWorks_thenCorrect(){String nullName=null;String name=Optional.ofNullable(nullName).orElseThrow(IllegalArgumentException::new);} 这个异常处理方法是从Java8 开始提供的,可以通过在构造来传入异常。 Java 10 以后,还推出了一个更加简单的没...
TheOptionalclass in Java provides a convenient way to handle scenarios where a value may be present or absent, avoiding the need for null checks. TheisPresentandisEmptymethods are used to check the presence or absence of a value within anOptionalobject. By using these methods, we can write ...
Java中空指针异常(NPE)一直是令开发者头疼的问题。Java 8引入了一个新的Optional类,使用该类可以尽可能地防止出现空指针异常。 Optional 类是一个可以为null的容器对象。如果值存在则isPresent()方法会返回true,调用get()方法会返回该对象。Optional提供很多有用的方法,这样开发者就不必显式进行空值检测。
Java documentation forjava.util.OptionalInt. Portions of this page are modifications based on work created and shared by theAndroid Open Source Projectand used according to terms described in theCreative Commons 2.5 Attribution License. Properties ...
Added in 1.8. Java documentation forjava.util.Optional. Portions of this page are modifications based on work created and shared by theAndroid Open Source Projectand used according to terms described in theCreative Commons 2.5 Attribution License. ...
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 ...
为了解决这种尴尬的处境,JDK 终于在 Java8 的时候加入了 Optional 类。用于避免空指针的出现,也无需在写大量的if(obj!=null)这样的判断了,前提是你得将数据用Optional装着,它就是一个包裹着对象的容器。 Optional 的 javadoc 介绍: A container object which may or may not contain a non-nullvalue. If a...