Unhandled Exception Type Error

unhandled exception type error

It means a method you're calling is declared with the throws directive for an exception derived from the Exception class. When a method is declared in this way, you are forced to deal with the exception using a try/catch block or add an identical throws (for the same exception or a super type) statement to your method declaration.

An example.

I want to call some method foo inside my method bar.

Here is foo's definition:

public static void foo(String a) throws Exception {
    // foo does something interesting here.
}

I want to call foo. If I simply do this:

private void bar() {
    foo("test");
}

...then I'll get the error you are experiencing. foo declares to the world that it really might decide to throw an Exception and you had better be ready to deal with it.

I have two options. I can change bar's definition as follows:

private void bar() throws Exception {
    foo("test");
}

Now I've publicized my own warning that my method or some method I call could throw an Exception that the user of my method should deal with. Since I've deferred responsibility to my method's caller, my method doesn't have to deal with the exception itself.

It's often better to deal with the exception yourself, if you can. That brings us to the second option, the try/catch:

private void bar() {
    try {
        foo("test");
    } catch(Exception e) {
        Log.wtf("MyApp", "Something went wrong with foo!", e);
    }
}

Now I've dealt with the potential Exception thrown by foo that the compiler was complaining about. Since it's been dealt with, I don't need to add a throws directive to my bar method.

Unhandled exception type Exception in Eclipse

You call teste.parse(someString), where teste is an expression which has type Parser. That means this is a call to the method parse(String) in your Parser type....

and that is declared with throws Exception.

Exceptions are a mechanism to convey alternate return options. The parse method can run its course in one of two ways: It can 'return', in which case it returns nothing (void), or, it can 'throw'. What it can throw is limited by its throws line - in this case, it can throw just about anything (Exception is the supertype of almost all things you can throw).

The way java handles this is that your code needs to handle every possible way a method can conclude.

So, you need a 'path' for your code when the parser() method returns (this is trivial; it's a void method, you get that 'for free', you don't need to write anything special for this), but you also need a path for that other exit scenario: When it throws something. You get handling of RuntimeException for free, but for others, you have two options:

catch it:

try {
    teste.parse(someString);
    // this code runs in the 'return' case.
} catch (Exception e) {
   // this code runs in the 'throws' case.
}

this would imply you know what to do when your parse method decided to exit via the throws path.

Alternatively, you fix this by having your main method also 'fork', and decree that it has two ways to finish: Either via the return route or the throw route:

public static void main(String[] args) throws Exception {
    teste.parse(someString);
}
// this main method has declared that it has two separate
// exit routes. 'return', and 'throws something'.

java will start an application by running its main method, and java can deal with a main that has two alternate exit routes (return, or throw something). It handles the 'return' route by doing nothing. It handles the 'throw something' route by printing the type of the exception, the message, the stack trace, and the entire causal chain. That is an excellent default, and you should not attempt to come up with a different one by e.g. catching that exception and attempting to 'log it'.

This: Just add throws Exception to your main method declaration. Put the throws Exception back on your parse method, ignore @Eritrean's advice.

NB: All methods are inherently declared as if they said throws RuntimeException, Error (as in, any error and any runtimeexception can be thrown without writing a throws clause for it, as all methods implicitly have that clause baked in already), this is why I said earlier that RuntimeExceptions are 'handled for free'. The idea is that all exceptions that subclass RuntimeException are things that are so universal or so unlikely, it would be unwieldy to force management of this onto the programmer. That's why you never need to write throws NullPointerException or throws InternalError.

Unhandled exception type Exception

Yes. It is a compilation error.

No. There is no special syntax to deal with this.

I do not want to catch Exception in method.

Unfortunately if you throw a checked exception, it has to be caught further up the call stack. That is a fundamental design principal for the Java language, and one that the compiler enforces strictly.

In this, case there is no way to catch the checked exception. Hence, if you are going to call a method in enum constant parameter (as per your code), the method cannot throw a checked exception¹.

Here is a possible workaround, though this is probably a bad idea:

public class Main {

    enum Test{
        First(methodCatchingException()){
            // ...
        };

        Test(Object obj){
            //...
        }
    }

    static Object method() throws Exception{
        // ...
        if (someCondition){
            throw new Exception();
        }
    }

    static Object methodCatchingException() {
        try {
            return method();
        } catch (Exception ex) {
            throw new SomeRuntimeException("the sky is falling!", ex);
        }
    }
}

Another way to look at this problem is to ask yourself what should happen with the exception if the compiler let you write that ... and an exception was thrown? Where would it go?

You can't catch it ... because the enum initialization is like a static initialization.
If the Java runtime completely ignored the thrown exception, that would be really bad.
If the Java runtime crashed, then the model of checked exceptions is broken.

So, what this is saying to me is that the Java language design is right, the Java compiler is right ... and the real problem here is in your application design:

You should not be propagating a checked exception here. If an exception occurs in this context it is categorically NOT a recoverable error.
Maybe it is inadvisable to use an enum for this ... because of the potential for non-recoverable initialization errors.

(Note that if this method call terminates due to an unchecked exception, it will turn it into an ExceptionInInitializerError. In addition, the JVM will mark the enum class as uninitializable, and will throw an NoClassDefFoundError if your application attempts to use it; e.g. via Class.forName(...).)

I assume that Exception is used here for illustration purposes. It is a bad thing to declare methods as throws Exception or to throw new Exception(...)

^{1 - I had a look at the JLS for something to back this up. As far as I can tell, the spec does not mention this situation. I'd have expected to see it listed in JLS 11.2.3. However, it is clear that a compiler cannot allow a checked exception to propagate at that point as it would "break" the model of how checked exceptions work.}

java: can't rethrow exception: Unhandled exception type Exception

I think there are various things to mention here:

You either want doJobWithResult() to return true on success and false on failure, or return nothing on success and throw an exception on failure.
Both at the same time is not possible. In the first case, catch the Exception, log it and return false, in the second case change your signature to return void and throw an exception and handle it in the caller.
It's a Don't to catch an exception, log it and rethrow it. Why? Because a potential caller of your method does not know that you are already logging it, and migh log it as well.
Either throw an exception (in which case the caller has to deal with it) or catch it and handle it (log it).
Note that throwing Exception does not give the caller of your method any clue about what might potentially go wrong in your method, it's always better to throw more specific exceptions, or to wrap an exception in a user-defined one and rethrow it.
Moreover, if you throw Exception, a caller might be tempted to catch Exception without noticing that this will also catch every RuntimeException (since its derived from Exception), which might not be desired behavior.

Error - Unhandled exception type Exception?

That's the difference between a "checked" exception and an "unchecked" exception. Anything that extends RuntimeException, including NullPointerException, are "unchecked" which means they don't need to be explicitly handled via a try/catch or by declaring that the method throw them.

Checked exceptions are those that do not extend RuntimeException and must be handled either by try/catch or by declaring your method throw it. So your code fails to compile because you are not handling it either way.

Unhandled exception type when Throwing exception inside a compact structure (StringConverter case)

Exceptions aren't just a funny name. You shouldn't use an exception just because the name sounds vaguely relevant. CharConversionException is about issues with charset encoding and e.g. XML reading; the point is, it extends IOException, so it is a kind of 'problem with an Input/Output channel', and it just doesn't apply here. Make your own exception types, or use one of the more general exception types that are intentionally designed (by reading the javadoc and checking the inheritance) to be a bit more nebulous. For example, IllegalArgumentException could be used here (if the argument doesn't start with a D or d, it is, apparently, illegal? Bit of a weird method).

The difference is in the kind of exception it is.

In java, throwables are checked, meaning, a method needs to catch all exceptions it throws, unless it explicitly decrees that it, itself, throws this. Thus, this does not compile:

public void test() {
    throw new IOException();
}

whereas this does:

public void test() throws IOException {
   throw new IOException();
}

And note that by invoking a method that declares that it throws something, you inherit this 'catch it or declare that you rethrow it'. Thus, this does not compile:

public void test2() {
   test(); // declared to `throws IOException`
}

whereas this does:

public void test2() throws IOException {
   test();
}

And note that public static void main(String[] args) is allowed to (and usually should!) be declared to just throws Exception.

Java has another rule baked in that explains why NumberFormatException gets a pass: All methods are assumed to throws RuntimeException, Error (as in, can throw both RuntimeException and Error instances), whether you write this or not.

Check the hierarchy of NumberFormatException: It is a specialization of RuntimeException, and thus, inherently all methods are declared to throws is. CharConversionException extends IOException extends Exception extends Throwable - nothing in that list is either RuntimeException or Error and therefore no pass is allowed.

To make matters worse, if you are implementing a method from a supertype (such as here; you are overriding the public String fromString(String arg) method), you can't just add new methods in your declaration. After all, you are writing a kind of StringConverter, which means anybody can treat an instance of your newly defined class as a StringConverter, and StringConverter's fromString method doesn't declare it, thus, you're stuck.

Fortunately, as I said, CharConversionException is not appropriate, but IllegalArgumentException might be, and IllegalArgumentException is unchecked (it extends RuntimeException, thus, you can freely throw it as all methods are silently assumed to do that).

Flutter : Unhandled Exception: type 'Listdynamic' is not a subtype of type 'Listdouble' in type cast

This is a task from the school course.

void main(List<String> args) {
  getPatientDataList().then((result) {
    final dataSize = result.length;
    final List<List<double>> list = result
        .getRange(1, 3)
        .map((e) => e.map((e) => e as double).toList())
        .toList();
    print("data " + list.toString());
  });
}

Future<List<List>> getPatientDataList() async {
  return <List<dynamic>>[
    [0.0, 0.5],
    [1.0, 1.5],
    [2.0, 2.5],
    [3.0, 3.5],
  ];
}

Output:

data [[1.0, 1.5], [2.0, 2.5]]

Or even...

void main(List<String> args) {
  getPatientDataList().then((result) {
    final dataSize = result.length;
    final List<List<double>> list =
        result.getRange(1, 3).map((e) => e.cast<double>()).toList();
    print("data " + list.toString());
  });
}

And so...

void main(List<String> args) {
  getPatientDataList().then((result) {
    final dataSize = result.length;
    final List<List<double>> list =
        List.of(result.getRange(1, 3).map((e) => e.cast()));   
    print("data " + list.toString());
  });
}

Unhandled Exception Type Error