Your question is obscure but here what you could ask:
In what cases catching certain exception is not ok, until the try block throws it? OK? If this is your question here you go:
1- If the you catch any subclass of Exception class, except subclasses of RuntimeException, you must throw that exception in the try block. 2- Even if you declare that exception in the method, but you catch it too, your code must throw that exception in the try block, otherwise code wont compiler. 3- RuntimeException (itself and its subclasses), you can throw it without putting try catch block or without declaring it in the method.