why can some methods in java throw a exception without handling it code example

Example: in java how to throw exception from function

public void doChangePin(int oldPin, int pin) throws Exception {	//need to add throws followed by exception name
		if (oldPin == pinCode) {
			pinCode = pin;
		} else {
			throw new Exception("some message");	//throwing the exception by creating its new object
		}
	}