Java方法包含另一个抛出异常的方法

Question

Inside Method A, there is method B. Method B throws exception, but method A compiled even it does not catch exception or throws exception, could it be possible?

Method B is something like as below:

MethodB() throws SomeException{
   if(Some)
        doneSomething
        return
   else if(some)
        donesomethingElse
        return 
   throw SomeException  
}

Answer 1

If the SomeException extends RuntimeException . Then you don't need to catch it even if the signature looks like that.

Also note that you can just remove the throws SomeException in that case. Read more here .

Answer 2

Yes, there are some unchecked exception, who might not be caught / rethrown.

Look at this tutorial - Unchecked Exceptions .

Answer 3

Even if SomeException is a checked exception, this can happen due to separate compilation.

Suppose you write a class:

public class B {
  public static void foo() {
  }
}

Then a class that calls it:

public class A {
  public static void main(String[] args) {
    B.foo();
  }
}

Then say:

javac A.java
java A

All is fine. Now change B:

public class B {
  public static void foo() throws java.io.IOException {
    throw new java.io.IOException();
  }
}

And this time just compile B before running:

javac B.java
java A

You get:

Exception in thread "main" java.io.IOException
    at B.foo(B.java:4)
    at A.main(A.java:4)

In the real world this happens when individual .jar files are updated after they've been modified by maintainers who don't understand the problems caused by adding more throws clauses.