java - 如果构造函数抛出异常，是否不调用 try-with-resources 习惯用法的 close 方法？

Question

我有一个基类 Base 和一个扩展它的子类 Child。 Base 实现了 java.lang.AutoCloseable。

假设 Child 的构造函数抛出一个 Foo。

现在考虑

try (Base c = new Child()){
    /*Some code*/
} catch (final Foo e){
    /*Some more code*/
}

如果抛出异常，是否调用Base#close方法？它不在我的机器上，但这是 JLS 标准化的东西吗？

Answer 1

是的，close 不会被调用。这在 JLS section 14.20.3 中指定:

Resources are initialized in left-to-right order. If a resource fails to initialize (that is, its initializer expression throws an exception), then all resources initialized so far by the try-with-resources statement are closed. If all resources initialize successfully, the try block executes as normal and then all non-null resources of the try-with-resources statement are closed.

Resources are closed in the reverse order from that in which they were initialized. A resource is closed only if it initialized to a non-null value. An exception from the closing of one resource does not prevent the closing of other resources. Such an exception is suppressed if an exception was thrown previously by an initializer, the try block, or the closing of a resource.

在这种情况下，构造函数中会抛出异常，因此资源不会初始化为非空值。因此，不会调用 close 方法。