Java 8 方法引用未处理的异常 [英] Java 8 method reference unhandled exception

问题描述

我正在使用 Java 8 进行项目，发现了一种我无法理解的情况.

I'm working on project with Java 8 and found one situation which I can't understand.

我有这样的代码:

void deleteEntity(Node node) throws SomeException {
    for (ChildNode child: node.getChildren()) {
       deleteChild(child);
    }
}

void deleteChild(Object child) throws SomeException {
    //some code
}

这段代码运行良好，但我可以使用方法引用重写它:

This code is working fine, but I can rewrite it with a method reference:

void deleteEntity(Node node) throws SomeException {
    node.getChildren().forEach(this::deleteChild);
}

并且这段代码无法编译，给出错误Incompatible throw types *SomeException* in method reference.

And this code doesn't compile, giving the error Incompatible thrown types *SomeException* in method reference.

IDEA 也给了我错误unhandled exception.

Also IDEA gave me the error unhandled exception.

所以，我的问题是为什么?为什么代码用 for 每个循环编译，而不用 lambda 编译?

So, my question is why? Why code compiles with for each loop and doesn't compile with lambda?

推荐答案

如果看Consumer 接口，accept 方法(这是您的方法引用将有效使用的方法)未声明为抛出任何已检查异常 - 因此您不能使用 被声明为 以抛出已检查异常的方法引用.增强的 for 循环没问题，因为您总是处于可以抛出 SomeException 的上下文中.

If you look at the Consumer<T> interface, the accept method (which is what your method reference would effectively be using) isn't declared to throw any checked exceptions - therefore you can't use a method reference which is declared to throw a checked exception. The enhanced for loop is okay, because there you're always in a context where SomeException can be thrown.

您可能会创建一个包装器，将已检查的异常转换为未检查的异常，然后抛出该异常.或者，您可以使用 accept() 方法声明自己的函数式接口，该方法确实抛出一个检查异常(可能使用该异常参数化接口)，然后编写自己的forEach 方法将该功能接口作为输入.

You could potentially create a wrapper which converts the checked exception to an unchecked exception, and throw that. Alternatively, you could declare your own functional interface with an accept() method which does throw a checked exception (probably parameterizing the interface with that exception), and then write your own forEach method that takes that functional interface as an input.

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