Exceptions

main.dart

void main() {
  int res = ComputeService().add(2, 4);
  print("Res: $res");
  
  try {
    int res = ComputeService().add(null, 4);
    print("Res: $res");
  } on ComputeServiceException catch (e){
    print("Error: ${e.cause}");
  }
  
  try {
    int res = SuperComputeService().add(3, 5);
    print("Res: $res");
  } catch (e){
    print("Error: ${e.cause}");
  }  
  
  res = ComputeService().substract(val1: 3);
  print("Res: $res");
}


class ComputeService {
  int substract({int val1, int val2=1}) {
    return val1 - val2;  
  }
  
  int add(int a, int b) {
    if (a == null) {
      throw ComputeServiceException("parameter a can not be null");
    }
    return a + b;
  }
}

class SuperComputeService implements ComputeService {
  int add(int a, int b) {
    if (a == null) {
      throw ComputeServiceException("parameter a can not be null");
    }
    return a + b;
  }
  
  int substract({int val1, int val2=1}) {
    return val1 - val2;  
  }
}


class ComputeServiceException implements Exception {
  String cause;
  ComputeServiceException(this.cause);
}