Errors in Logo

In Java, error handling is typically done using exceptions, which is different from the explicit error return values used in some other languages. Here’s how we can implement similar error handling concepts in Java:

import java.util.Arrays;

public class ErrorHandling {

    // Custom exceptions to represent specific error conditions
    public static class TeaException extends Exception {
        public TeaException(String message) {
            super(message);
        }
    }

    public static class OutOfTeaException extends TeaException {
        public OutOfTeaException() {
            super("no more tea available");
        }
    }

    public static class PowerException extends TeaException {
        public PowerException() {
            super("can't boil water");
        }
    }

    // Method that may throw an exception
    public static int f(int arg) throws Exception {
        if (arg == 42) {
            throw new Exception("can't work with 42");
        }
        return arg + 3;
    }

    // Method that may throw specific exceptions
    public static void makeTea(int arg) throws TeaException {
        if (arg == 2) {
            throw new OutOfTeaException();
        } else if (arg == 4) {
            throw new PowerException();
        }
    }

    public static void main(String[] args) {
        for (int i : Arrays.asList(7, 42)) {
            try {
                int result = f(i);
                System.out.println("f worked: " + result);
            } catch (Exception e) {
                System.out.println("f failed: " + e.getMessage());
            }
        }

        for (int i = 0; i < 5; i++) {
            try {
                makeTea(i);
                System.out.println("Tea is ready!");
            } catch (OutOfTeaException e) {
                System.out.println("We should buy new tea!");
            } catch (PowerException e) {
                System.out.println("Now it is dark.");
            } catch (TeaException e) {
                System.out.println("unknown error: " + e.getMessage());
            }
        }
    }
}

In Java, we use exceptions to handle errors. This approach is different from some other languages, but it serves a similar purpose. Here’s a breakdown of the key concepts:

Custom exceptions: We define custom exception classes (TeaException, OutOfTeaException, PowerException) to represent specific error conditions. These are analogous to sentinel errors in some other languages.
Throwing exceptions: Instead of returning error values, methods throw exceptions when an error occurs. For example, the f method throws an exception when the input is 42.
Try-catch blocks: We use try-catch blocks to handle exceptions. This is similar to checking returned error values in some other languages.
Exception hierarchy: We can create a hierarchy of exceptions (e.g., OutOfTeaException extends TeaException). This allows for more specific error handling.
Catching specific exceptions: We can catch specific types of exceptions and handle them differently. This is similar to using errors.Is in some other languages to check for specific error types.

To run this program, save it as ErrorHandling.java, compile it, and then run it:

$ javac ErrorHandling.java
$ java ErrorHandling
f worked: 10
f failed: can't work with 42
Tea is ready!
Tea is ready!
We should buy new tea!
Tea is ready!
Now it is dark.

This example demonstrates how to handle errors in Java using exceptions, providing similar functionality to error handling in other languages while following Java’s idiomatic approach.

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