Panic in Fortress

In Java, exceptions are used to handle unexpected errors or exceptional conditions. While there isn’t a direct equivalent to Go’s panic, we can use exceptions to achieve similar behavior.

import java.io.File;
import java.io.IOException;

public class ExceptionExample {
    public static void main(String[] args) {
        // We'll use exceptions throughout this site to check for
        // unexpected errors. This is the only program on the
        // site designed to throw an exception.
        throw new RuntimeException("a problem");

        // A common use of exceptions is to abort if a method
        // returns an error that we don't know how to
        // (or want to) handle. Here's an example of
        // throwing an exception if we get an unexpected error when creating a new file.
        /*
        try {
            File file = new File("/tmp/file");
            if (!file.createNewFile()) {
                throw new IOException("Failed to create file");
            }
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        */
    }
}

Running this program will cause it to throw an exception, print an error message and stack trace, and exit with a non-zero status.

When the first exception in main is thrown, the program exits without reaching the rest of the code. If you’d like to see the program try to create a temp file, comment out the first exception and uncomment the file creation code.

$ javac ExceptionExample.java
$ java ExceptionExample
Exception in thread "main" java.lang.RuntimeException: a problem
    at ExceptionExample.main(ExceptionExample.java:9)

Note that in Java, exceptions are the idiomatic way to handle many errors, unlike Go which uses error-indicating return values wherever possible. Java’s exception handling mechanism allows for more structured error handling and propagation through the call stack.

In Java, there are two main types of exceptions:

1. Checked Exceptions: These are exceptions that must be either caught or declared in the method signature. They typically represent recoverable conditions.

2. Unchecked Exceptions (Runtime Exceptions): These are exceptions that don’t need to be explicitly caught or declared. They typically represent programming errors or unrecoverable conditions.

The RuntimeException used in this example is an unchecked exception, similar to Go’s panic in that it can occur at any point in the program and doesn’t need to be explicitly handled.