Java extend abstract class with external class

Question

I want to have a single abstract class InitException to represent a set of classes, ie StartParameterException , FileNotFoundException , etc. I define StartParameterException myself, but FileNotFoundException is a standard exception that I import. So I can not add extends InitException to its definition, as I do for my own classes:

public class StartParameterException extends InitException {
    ...
}

The main point is to change this:

try {
    ...
} catch (StartParameterException | FileNotFoundException | InvalidPathException | NullBoardException e) {
    System.out.println(e);
    System.exit(INIT_ERROR);
}

to this

try {
    ...
} catch (InitException e) {
    System.out.println(e);
    System.exit(InitException.ERROR_CODE);
}

Is this possible? Should I use an interface somehow?

Answer 1

You may try to create a set of exception classes. And then check whether the caught exception is within the set

Set<Class<?>> setClassesInitExc = new HashSet<>();
setClassesInitExc.add(FileNotFoundException.class);
setClassesInitExc.add(InvalidPathException.class);
setClassesInitExc.add(StartParameterException.class);
setClassesInitExc.add(NullBoardException.class);

try {
    ...     
} catch(Exception e) {
    if (setClassesInitExc.contains(e.getClass())) {
        System.out.println(e);
        System.exit(InitException.ERROR_CODE);     
    }
}

Answer 2

Another way is to create an enum with supported exception types and add some context required to handle each exception, something like this:

public enum ExceptionEnum {
    START_PARAMETER_EXCEPTION(StartParameterException.class, "Start parameter exception occurred", 1),
    FILE_NOT_FOUND_EXCEPTION(FileNotFoundException.class, "Required file is not found", 2),
    INVALID_PATH_EXCEPTION(InvalidPathException.class, "Given path is not valid", 3),
    NULL_BOARD_EXCEPTION(NullBoardException.class, "Null board exception occurred", 4);

    private Class exceptionClass;
    private String errorMessage;
    private int exitCode;

    public Class getExceptionClass() {
        return exceptionClass;
    }

    public String getErrorMessage() {
        return errorMessage;
    }

    public int getExitCode() {
        return exitCode;
    }

    ExceptionEnum(Class exceptionClass, String errorMessage, int exitCode) {
        this.exceptionClass = exceptionClass;
        this.errorMessage = errorMessage;
        this.exitCode = exitCode;
    }

    public static ExceptionEnum fromExceptionClass(Class clazz) {
        for (ExceptionEnum exceptionEnum : ExceptionEnum.values()) {
            if (exceptionEnum.getExceptionClass().isAssignableFrom(clazz)) {
                return exceptionEnum;
            }
        }
        return null;
    }
}

More context to each exception can be added and this provides more control on how individual exceptions can be handled at run time:

try {
  //....
    } catch (Exception e) {
   ExceptionEnum exceptionEnum = ExceptionEnum.fromExceptionClass(e.getClass());
        if(exceptionEnum != null) {
            System.out.println(exceptionEnum.getErrorMessage());
            System.exit(exceptionEnum.getExitCode());   
        }
    }