Custom Errors in Minitab

Custom errors in Java are typically implemented using custom exception classes. Here’s an equivalent implementation of the custom error example:

import java.util.function.Function;

// A custom exception class usually extends Exception or RuntimeException
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 CustomErrors {
    // This method can throw our custom exception
    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) {
            // In Java, we use instanceof to check the type of an exception
            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");
            }
        }
    }
}

In this Java implementation:

1. We define a custom exception class ArgException that extends Exception. This is equivalent to the argError struct in the original code.

2. The ArgException class includes a constructor that takes an arg and a message, similar to the fields in the original argError struct.

3. We override the toString() method to provide a custom string representation of the exception, similar to the Error() method in the original code.

4. The f method is implemented to throw our custom exception when the argument is 42.

5. In the main method, we use a try-catch block to handle the exception. We use instanceof to check if the caught exception is of type ArgException, which is similar to the errors.As function in the original code.

6. If the exception is an ArgException, we cast it and access its properties. Otherwise, we print a message indicating that the exception doesn’t match ArgException.

To run the program:

$ javac CustomErrors.java
$ java CustomErrors
42
can't work with it

This Java implementation provides equivalent functionality to the original code, using Java’s exception handling mechanism instead of Go’s error interface.