RuntimeException in Java Hierarchy

Direct Answer

RuntimeException is the unchecked branch under Exception. Java does not require callers to catch its subclasses or declare them with throws. Types such as NullPointerException, IllegalArgumentException, and IllegalStateException often report invalid use or broken invariants, but applications also use unchecked exceptions for translated infrastructure and domain failures; the name does not mean other exceptions occur outside runtime.

Code Example

public class OrderService {
    // No 'throws' needed for unchecked exceptions
    public Order createOrder(Long userId, List<String> items) {
        if (userId == null)
            throw new IllegalArgumentException("userId must not be null");
        if (items.isEmpty())
            throw new IllegalStateException("order needs at least one item");
        return new Order(userId, items);
    }

    // A checked exception DOES force a throws declaration
    public String readNotes(String path) throws java.io.IOException {
        return java.nio.file.Files.readString(java.nio.file.Path.of(path));
    }
}

IllegalArgumentException/IllegalStateException are unchecked; the caller is free to ignore them because catch-or-declare does not apply.

Common Mistakes & Pitfalls

• Thinking runtime refers to when it occurs: all exceptions are thrown during execution; this name marks an unchecked branch.
• Calling every RuntimeException a coding bug: frameworks and applications also use unchecked domain and translated infrastructure failures.
• Catching every RuntimeException broadly: catch a specific type only when this layer can act.
• Adding throws RuntimeException as if required: declaring unchecked failures is optional documentation.
• Hiding invalid input: validate at the boundary with a meaningful subtype and message.