Common Checked Exceptions in Java

Direct Answer

The most common checked exceptions are IOException (and subtypes like FileNotFoundException), SQLException (JDBC), InterruptedException (thread interruption), ClassNotFoundException (reflection/class loading), and ParseException. They all extend Exception (not RuntimeException), so the compiler forces you to catch or declare them — their APIs require callers to acknowledge the failure at compile time.

Deep Dive & Architecture

IOException is the base for many file and stream failures, including FileNotFoundException. SQLException reports database-access failures and can carry SQL state and a vendor code. InterruptedException tells blocking code that another thread requested interruption; handling it is part of a cancellation policy. ClassNotFoundException is used when code asks for a class by name and the loader cannot find it. ParseException belongs to APIs such as SimpleDateFormat that report checked parsing failure.

The shared fact is structural: each is under Exception but outside RuntimeException, so catch-or-declare applies. Do not invent one universal response such as retrying. A missing file might use a default, a database failure might be translated, interruption may stop a task, and a bad import file may be reported to the user.

Code Example

// IOException (checked) -- reading a file
String cfg = Files.readString(Path.of("app.conf"));        // throws IOException

// SQLException (checked) -- JDBC
try (Connection c = ds.getConnection()) { /* ... */ }       // throws SQLException

// InterruptedException (checked) -- blocking call
try {
    Thread.sleep(1000);
} catch (InterruptedException e) {
    Thread.currentThread().interrupt();   // restore the interrupt flag
}

// ClassNotFoundException (checked) -- reflection
Class<?> c = Class.forName("com.example.Plugin");           // throws ClassNotFoundException

All five are checked because they model conditions outside your code where recovery makes sense.

Common Mistakes & Pitfalls

• Calling NullPointerException/IllegalArgumentException checked — they're unchecked (RuntimeException).
• Not knowing InterruptedException is checked — and forgetting to restore the interrupt flag.
• Swallowing SQLException with an empty catch instead of rolling back/logging.
• Assuming all I/O is one type — FileNotFoundException is a specific IOException subtype.