It's possible to use custom types as exceptions by extending the `Exception` class. Here's an example that uses a custom type to explicitly represent an argument error.

```java
import java.util.Optional;

// A custom exception type usually has the suffix "Exception".
class ArgException extends Exception {
    private int arg;

    public ArgException(int arg, String message) {
        super(message);
        this.arg = arg;
    }

    public int getArg() {
        return arg;
    }

    @Override
    public String toString() {
        return arg + " - " + getMessage();
    }
}

public class CustomExceptions {
    public static int f(int arg) throws ArgException {
        if (arg == 42) {
            // Throw our custom exception.
            throw new ArgException(arg, "can't work with it");
        }
        return arg + 3;
    }

    public static void main(String[] args) {
        try {
            f(42);
        } catch (Exception e) {
            // instanceof is used to check if an exception is of a specific type.
            // It's similar to errors.As in Go.
            if (e instanceof ArgException) {
                ArgException ae = (ArgException) e;
                System.out.println(ae.getArg());
                System.out.println(ae.getMessage());
            } else {
                System.out.println("e doesn't match ArgException");
            }
        }
    }
}