Is there a way to throw an exception without adding the throws declaration?
JavaExceptionJava Problem Overview
I have the following situation.
I have a Java Class that inherits from another base class and overrides a method.
The base method does not throw exceptions and thus has no throws ...
declaration.
Now my own method should be able to throw exception but I have the choices to either
- Swallow the exception or
- Add a throws declaration
Both a not satisfying because the first one would silently ignore the exception (ok I could perform some logging) and the second would generate compiler errors because of the different method headers.
public class ChildClass extends BaseClass {
@Override
public void SomeMethod() {
throw new Exception("Something went wrong");
}
}
Java Solutions
Solution 1 - Java
You can throw unchecked exceptions without having to declare them if you really want to. Unchecked exceptions extend RuntimeException
. Throwables that extend Error
are also unchecked, but should only be used for completely un-handleable issues (such as invalid bytecode or out of memory).
As a specific case, Java 8 added UncheckedIOException
for wrapping and rethrowing IOException
.
Solution 2 - Java
Here is a trick:
class Utils
{
@SuppressWarnings("unchecked")
private static <T extends Throwable> void throwException(Throwable exception, Object dummy) throws T
{
throw (T) exception;
}
public static void throwException(Throwable exception)
{
Utils.<RuntimeException>throwException(exception, null);
}
}
public class Test
{
public static void main(String[] args)
{
Utils.throwException(new Exception("This is an exception!"));
}
}
Solution 3 - Java
A third option is to opt out of exception checking (just like the Standard API itself has to do sometimes) and wrap the checked exception in a RuntimeException
:
throw new RuntimeException(originalException);
You may want to use a more specific subclass of RuntimeException
.
Solution 4 - Java
I just want do add an alternative answer, purely as an FYI:
Yes, there is a way to throw a checked exception without adding the throws
declaration, by using the sun.misc.Unsafe
class. This is described in the following blog post:
Throw a checked exception from a method without declaring it
Sample code:
public void someMethod() {
//throw a checked exception without adding a "throws"
getUnsafe().throwException(new IOException());
}
private Unsafe getUnsafe() {
try {
Field field = Unsafe.class.getDeclaredField("theUnsafe");
field.setAccessible(true);
return (Unsafe) field.get(null);
} catch (Exception e) {
throw new RuntimeException(e);
}
}
However, this is not recommended. It is better to wrap in an unchecked exception as outlined in the some of the other answers.
Solution 5 - Java
Why don't you throw an unchecked exception? This doesn't have to be declared.
Two alternatives are
- wrap with a checked exception with an unchecked one.
- don't let the compiler know you are throwing a checked exception e.g. Thread.currentThread().stop(e);
- In Java 6, you can rethrow the exception if it is
final
and the compiler know which checked exceptions you might have caught. - In Java 7, you can rethrow an exception if it is effectively final, i.e. you don't change it in code.
The later is more useful when you are throwing a check exception in you code and catching it in your calling code, but the layers inbetween don't know anything about the exception.
Solution 6 - Java
Yes there is a why but it is not recommended at all you can use :
> Java unsafe package
getUnsafe().throwException(new IOException());
This method throws checked exception, but your code not forced to catch or rethrow it. Just like runtime exception.
Solution 7 - Java
Here's an example for intercepting checked exceptions and wrapping them in an unchecked exception:
public void someMethod() {
try {
doEvil();
}
catch (IOException e)
{
throw new RuntimeException(e);
}
}
Solution 8 - Java
If you use Project lombok and want to throw checked exceptions without the throws
declaration, you can add @SneakyThrows
to the method:
public void yourCaller(){
yourMethod();
}
@SneakyThrows
public void yourMethod(){
throw new Exception("Something went wrong");
}
This can throw checked exceptions without the caller needing to catch them.
Lombok provides an annotation processor that modifies the code at compile-time. With @SneakyThrows
, it catches and re-throws the exception without the throws
declaration.
As described in the description of @SneakyThrows
, it transforms code into something like that:
public void yourMethod() {
try {
throw new Exception("Something went wrong");
} catch (Exception t) {
throw Lombok.sneakyThrow(t);
}
}
From the sources of Lombok.sneakyThrow()
:
public static RuntimeException sneakyThrow(Throwable t) {
if (t == null) throw new NullPointerException("t");
return Lombok.<RuntimeException>sneakyThrow0(t);
}
@SuppressWarnings("unchecked")
private static <T extends Throwable> T sneakyThrow0(Throwable t) throws T {
throw (T)t;
}
As you can see, it uses generics to trick Java into thinking that this would be an unchecked exception as shown in this answer.
Solution 9 - Java
In Java 8, throwing a checked exception without declaring it can be done more easily due to type inference.
public class Main {
public static void main(String[] args) {
throwException(new Exception("exception"));
}
public static <T extends Throwable> void throwException(Throwable t) throws T {
throw (T) t;
}
}
Solution 10 - Java
Yes there is, using typecast to Runtime exception and throws a runtime exception.
Create an Exception helper class like this.
public class ExceptionHelper {
public static <T> void throwException(Throwable t) throws Throwable {
throw (Throwable) t;
}
}
class ServiceClass {
public void actualFlow() {
try {
//somethinf
} catch (Exception e) {
ExceptionHelper.throwException(e);
}
}
}
Solution 11 - Java
you can catch the exception with try- catch block in your method overridden. then you don't need to declare throws- statement.
Solution 12 - Java
You can use any exception derived from RuntimeException or RuntimeException itself
or
use a try-block for the exception throwing code and handle it there