Checked vs Unchecked

Comparison

	Checked	Unchecked
Extends	`Exception` (not RuntimeException)	`RuntimeException`
Compiler forces handling	yes: catch it or declare `throws`	no
Represents	expected problems outside your control (file missing, network down)	programming bugs (null, bad index, bad argument)
Examples	`IOException`, `SQLException`, `InterruptedException`	`NullPointerException`, `IllegalArgumentException`

The Compiler Checks Checked Exceptions

import java.nio.file.Files;
import java.nio.file.Path;

public class Main {
    public static void main(String[] args) {
        String text = Files.readString(Path.of("data.txt"));
        // error: unreported exception IOException; must be caught or declared to be thrown
    }
}

Example

Two ways to fix it: catch it, or declare it with throws and let the caller decide.

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;

public class Main {
    static String readConfig(String name) throws IOException {     // option 2: declare
        return Files.readString(Path.of(name));
    }

    public static void main(String[] args) {
        try {                                                       // option 1: catch
            System.out.println(readConfig("missing-config.txt"));
        } catch (IOException e) {
            System.out.println("Could not read config: " + e.getClass().getSimpleName());
        }
    }
}

Output

Could not read config: NoSuchFileException