第二部分:Java 8 Optional 的引入 Optional 的概念 Optional是一个容器,表示一个可能存在或不存在的值。它的设计目的是提供一种更清晰的方式来处理缺失值。 importjava.util.Optional;publicclassOptionalExample{publicstaticvoidmain(String[] args){ Optional<String> optionalValue = Optional.of("Hello"); System...
Exception in thread"main"java.lang.NullPointerException at java.util.Objects.requireNonNull(Objects.java:203) at java.util.Optional.<init>(Optional.java:96) at java.util.Optional.of(Optional.java:108) at club.mydlq.OptionalExample.main(OptionalExample.java:12) 可以看到传入正常参数正常返回 Optiona...
For example, field members of objects are automatically initialized to null, and programmers typically initialize reference types to null when they don’t have an initial value to give them. In general, null is used everytime where we don’t know, or we don’t have a value to give to a...
具体可以参考这个答案Optional无疑是一个糟糕的设计，更适合 Java 的演化方向应该是在 Java 8 时增强空...
For example, * {@code IllegalStateException::new} * * @param <X> Type of the exception to be thrown * @param exceptionSupplier The supplier which will return the exception to * be thrown * @return the present value * @throws X if there is no value present * @throws NullPointer...
Example Explanation In this section, we'll take a bit of time to explain the previous example withflatMapsandmaps. If you understand it without further explanation, please feel free to skip this section. The first method call is performed onfalconwhich is of typeOptional<Spaceship>. Calling th...
* the need to explicitly check for a return status. For example, the * following code traverses a stream of file names, selects one that has * not yet been processed, and then opens that file, returning an * {@code Optional<FileInputStream>}: ...
This method supports post-processing on optional values, without the need to explicitly check for a return status. For example, the following code traverses a stream of file names, selects one that has not yet been processed, and then opens that file, returning anOptional<FileInputStream>: ...
Exception in thread "main" java.lang.ArithmeticException at java.util.Optional.orElseThrow(Optional.java:290) at org.example.Main.main(Main.java:9) 二、Optional 中方法的区别 1、map 和 flatMap 方法的区别 map 方法会在返回时用 Optional 进行包装而 flatMap 方法不会再进行额外的包装。
In the following example, we have a simple example withOptionaltype. Main.java import java.util.Arrays; import java.util.Optional; void main() { var words = Arrays.asList("rock", null, "mountain", null, "falcon", "sky"); for (int i = 0; i < 5; i++) { ...