Java 9中Optional.ifPresentOrElse()和Optional.or()方法之间的区别是什么？

在Java 9版本中，引入了Optional.ifPresentOrElse()和Optional.or()方法来改进其功能。 Optional.ifPresentOrElse()方法检查值是否存在，如果存在则应用具有值的操作，否则返回空操作，而Optional.or()方法检查值是否存在，如果存在则返回包含值的选项，否则返回应用于Supplier函数的Optional。 Optional.ifPresentOrElse()方法包含两个参数，Consumer和Runnable，而Optional.or()方法只包含一个参数，Supplier。

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Optional.ifPresentOrElse()的语法：

<strong>public void ifPresentOrElse(Consumer<? super T><!--? super T--> action, Runnable emptyAction)</strong>

Example

示例

import java.util.Optional;
import java.util.concurrent.atomic.AtomicInteger;

public class IfPresentOrElseMethodTest {
   public static void main(String args[]) {
      optionalIsPresent();
      optionalIsEmpty();
   }
   private static void optionalIsPresent() {
      <strong>Optional<String></strong> optional = <strong>Optional.of</strong>("Test");
      AtomicInteger successCounter = new AtomicInteger();
      AtomicInteger emptyOptionalsCounter = new AtomicInteger();

      optional.<strong>ifPresentOrElse</strong>(x -> successCounter.incrementAndGet(), () ->       emptyOptionalsCounter.incrementAndGet());

      System.out.println(successCounter.get());
      System.out.println(emptyOptionalsCounter.get());
   }
   private static void optionalIsEmpty() {
      Optional optional = <strong>Optional.empty()</strong>;
      AtomicInteger successCounter = new AtomicInteger();
      AtomicInteger emptyOptionalsCounter = new AtomicInteger();

      optional.<strong>ifPresentOrElse</strong>(x -> successCounter.incrementAndGet(), () -> emptyOptionalsCounter.incrementAndGet());

      System.out.println(successCounter.get());
      System.out.println(emptyOptionalsCounter.get())
   }
}

输出

<strong>1
0
0
1</strong>

Optional.or()的语法：

<strong>public Optional<T> or(Supplier<? extends Optional<? extends T<!--? extends Optional<? extends T-->>> supplier)</strong>

Example

示例

import java.util.Optional;

public class OptionalOrMethodTest {
   public static void main(String args[]) {
      optionalIsPresent();
      optionalIsEmpty();
   }
   private static void optionalIsPresent() {
      <strong>Optional<String></strong> optional1 = <strong>Optional.of</strong>("Test1");
      <strong>Optional<String></strong> optional2 = <strong>Optional.of</strong>("Test2");

      <strong>Optional<String</strong><strong>></strong> optional3 = <strong>optional1.or</strong>(() -> optional2);
      System.out.println(optional3.get());
   }
   private static void optionalIsEmpty() {
      <strong>Optional<String></strong> optional1 = <strong>Optional.empty()</strong>;
      <strong>Optional<String></strong> optional2 = <strong>Optional.of</strong>("Test2");

      <strong>Optional<String></strong> optional3 = <strong>optional1.or</strong>(() -> optional2);
      System.out.println(optional3.get());
   }
}

输出

<strong>Test1
Test2</strong>