Java 9中Optional.ifPresentOrElse()和Optional.or()方法之间的区别？
无论Optional.ifPresentOrElse()和Optional.or()方法在Java的版本9中引入了以改善其功能。该Optional.ifPresentOrElse()方法检查值存在，适用行动值，否则返回空的动作，而Optional.or()方法检查值存在，返回选项包含的值，否则返回可选适用于供应商功能可按。Optional.ifPresentOrElse()方法包含两个参数，消费者 和可运行 而Optional.or()方法仅包含一个参数，供应商。
Optional.ifPresentOrElse()的语法：
public void ifPresentOrElse(Consumer<? super T> action, Runnable emptyAction)
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() {
Optional<String> optional = Optional.of("Test");
AtomicInteger successCounter = new AtomicInteger();
AtomicInteger emptyOptionalsCounter = new AtomicInteger();
optional.ifPresentOrElse(x -> successCounter.incrementAndGet(), () -> emptyOptionalsCounter.incrementAndGet());
System.out.println(successCounter.get());
System.out.println(emptyOptionalsCounter.get());
}
private static void optionalIsEmpty() {
Optional optional = Optional.empty();
AtomicInteger successCounter = new AtomicInteger();
AtomicInteger emptyOptionalsCounter = new AtomicInteger();
optional.ifPresentOrElse(x -> successCounter.incrementAndGet(), () -> emptyOptionalsCounter.incrementAndGet());
System.out.println(successCounter.get());
System.out.println(emptyOptionalsCounter.get())
}
}输出结果
1 0 0 1
Optional.or()的语法：
public Optional<T> or(Supplier<? extends Optional<? extends T>> supplier)
示例
import java.util.Optional;
public class OptionalOrMethodTest {
public static void main(String args[]) {
optionalIsPresent();
optionalIsEmpty();
}
private static void optionalIsPresent() {
Optional<String> optional1 = Optional.of("Test1");
Optional<String> optional2 = Optional.of("Test2");
Optional<String> optional3 = optional1.or(() -> optional2);
System.out.println(optional3.get());
}
private static void optionalIsEmpty() {
Optional<String> optional1 = Optional.empty();
Optional<String> optional2 = Optional.of("Test2");
Optional<String> optional3 = optional1.or(() -> optional2);
System.out.println(optional3.get());
}
}输出结果
Test1 Test2