I have a base class Base
and a child class Child
which extends it. Base
implements java.lang.AutoCloseable
.
Let's suppose that the constructor for Child
throws a Foo
.
Now consider
try (Base c = new Child()){
/*Some code*/
} catch (final Foo e){
/*Some more code*/
}
Is the Base#close
method called if the exception is thrown? It is not on my machine, but is this something that the JLS has standardised?
When an exception is thrown the method stops execution right after the "throw" statement. Any statements following the "throw" statement are not executed.
The try -with-resources statement is a try statement that declares one or more resources. A resource is an object that must be closed after the program is finished with it. The try -with-resources statement ensures that each resource is closed at the end of the statement.
For try-with-resources, if an exception is thrown in a try block and in a try-with-resources statement, then the method returns the exception thrown in the try block. The exceptions thrown by try-with-resources are suppressed, i.e. we can say that try-with-resources block throws suppressed exceptions.
The try statement allows you to define a block of code to be tested for errors while it is being executed. The catch statement allows you to define a block of code to be executed, if an error occurs in the try block.
Yes, close
won't be called. This is specified in the JLS section 14.20.3:
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.
In this case, an exception is thrown in the constructor so the resource is not initialized to a non-null value. Hence, the close
method isn't called.
close
will not be called. It wouldn't make sense to call it, since you don't have a fully-constructed object to close, and in similar calls, you might not have even entered a constructor:
try (Base b = makeBase()) {
...
}
where makeBase
is
Base makeBase() {
throw new RuntimeException();
}
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