Panic in Squirrel

In Java, exceptions are used to handle unexpected errors or exceptional conditions. The equivalent of a panic in Java is throwing an unchecked exception, typically a RuntimeException.

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.

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

Note that unlike some languages which use exceptions for handling of many errors, in Java it is common to use both exceptions and error-indicating return values, depending on the situation. Checked exceptions are often used for recoverable errors, while unchecked exceptions (like RuntimeException) are used for programming errors or unrecoverable situations.

The Java equivalent of a panic is generally an uncaught exception. When an uncaught exception occurs, the JVM prints the exception message and stack trace, then terminates the program. This behavior is similar to a panic in other languages.

Remember that in Java, it’s good practice to catch and handle exceptions appropriately when possible, rather than letting them propagate and crash the program. However, for truly unexpected and unrecoverable errors, allowing an uncaught exception to terminate the program can be a valid approach.