Difference between "throw new Exception" and "new Exception"?

Question

I am interested to know best practice to use throw new Exception() and new Exception(). In case of using new Exception(), I have seen that code moves to next statement instead of throwing exception.

But I am told that we should use new Exception() to throw RuntimeException.

Can anyone throw some light on this ?

Answer 1

new Exception() means create an instance (same as creating new Integer(...)) but no exception will happen until you throw it...

Consider following snippet:

public static void main(String[] args) throws Exception {
    foo(1);
    foo2(1);
    }

    private static void foo2(final int number) throws Exception {
    Exception ex;
    if (number < 0) {
        ex = new Exception("No negative number please!");
        // throw ex; //nothing happens until you throw it
    }

    }

    private static void foo(final int number) throws Exception {
    if (number < 0) {
        throw new Exception("No negative number please!");
    }

    }

the method foo() will THROW an exception if the parameter is negative but the method foo2() will create an instance of exception if the parameter is negative

Answer 2

Exception e = new Exception ();

Just creates a new Exception, which you could later throw. Using

throw e;

Whereas

throw new Exception()

Creates and throws the exception in one line

To create and throw a runtime exception

throw new RuntimeException()