The finally Block

Direct Answer

A finally block normally runs when control leaves its matching try, whether by normal completion, return, or an exception. It is not an absolute guarantee: JVM termination, process failure, forced halt, or code that never leaves the try can prevent it. Prefer try-with-resources for AutoCloseable resources because it closes them in reverse order and preserves close failures as suppressed exceptions.

Code Example

// Old approach: manual finally block
public String readFileLegacy(String path) throws IOException {
    BufferedReader reader = null;
    try {
        reader = new BufferedReader(new FileReader(path));
        return reader.readLine();
    } catch (IOException e) {
        System.err.println("Error reading file");
        throw e;
    } finally {
        if (reader != null) {
            reader.close(); // always called, even if return was executed
        }
    }
}

// Modern approach: try-with-resources (Java 7+)
public String readFileModern(String path) throws IOException {
    try (var reader = new BufferedReader(new FileReader(path))) {
        return reader.readLine(); // reader.close() called automatically
    } catch (IOException e) {
        System.err.println("Error reading file");
        throw e;
    }
    // No finally needed! Try-with-resources handles cleanup
}

Common Mistakes & Pitfalls

• Forgetting null check in finally: Calling resource.close() without checking if resource is null first causes NullPointerException if the resource wasn't successfully created.
• Not knowing finally runs on return: Freshers think return statements exit immediately, not realizing finally still executes afterward. This matters when finally modifies return values or closes resources.
• Using finally for resources with AutoCloseable: Writing manual finally blocks for file or database cleanup when try-with-resources is simpler and less error-prone. Try-with-resources should be the default choice now.