java - 捕获异常会捕获该异常的父类

Question

在 Java 中，我有一个方法捕获扩展“NewException”的异常“ChildException”。如果该方法调用另一个抛出“NewException”的方法，并且假设发生了某些事情并抛出它；捕获抛出异常的子类的调用者方法会捕获它吗？

public MethodCatchingChildException
{
  try
  {
     //stuff
     callingMethodThrowingNewException();
     //stuff
  }
  catch (ChildException e)
  {
     //stuff
  }
}

那么，调用MethodThrowingNewException的异常会被MethodCatchingChildException捕获吗？

Answer 1

catch 子句将捕获与声明的异常类型赋值兼容的任何异常。在您描述的情况下，NewException 实例(不是 ChildException)不会被该 catch 子句捕获，因为您无法将 NewException 对象分配给 ChildException 变量。

规则在 section 14.20.1 of the Java Language Specification 中有详细说明。 :

If execution of the try block completes abruptly because of a throw of a value V, then there is a choice:

• If the run-time type of V is assignment compatible with (§5.2) a catchable exception class of any catch clause of the try statement, then the first (leftmost) such catch clause is selected. The value V is assigned to the parameter of the selected catch clause, and the Block of that catch clause is executed, and then there is a choice:

  • If that block completes normally, then the try statement completes normally.

  • If that block completes abruptly for any reason, then the try statement completes abruptly for the same reason.

• If the run-time type of V is not assignment compatible with a catchable exception class of any catch clause of the try statement, then the try statement completes abruptly because of a throw of the value V.