Exceptions¶

Basic handling¶

try {
    int value = Integer.parseInt(text);
    System.out.println(value);
} catch (NumberFormatException exception) {
    System.err.println("Not an integer: " + text);
}

Catch the most specific exception that the current boundary can handle meaningfully.

Checked and unchecked exceptions¶

Checked exceptions derive from Exception but not RuntimeException; callers must catch or declare them.
Unchecked exceptions derive from RuntimeException; they often indicate invalid arguments, state, or programming mistakes.
Errors derive from Error and generally are not application recovery mechanisms.

Throwing and declaring¶

static int requirePositive(int value) {
    if (value <= 0) {
        throw new IllegalArgumentException("value must be positive");
    }
    return value;
}

static String read(Path path) throws IOException {
    return Files.readString(path);
}

Try-with-resources¶

try (var lines = Files.lines(path)) {
    lines.forEach(System.out::println);
}

Resources implementing AutoCloseable are closed automatically, including when an exception occurs. Prefer this to manual closing in finally.

Multiple exceptions¶

catch (IOException | SecurityException exception) {
    System.err.println(exception.getMessage());
}

Alternatives in a multi-catch cannot have a subtype relationship.

Repository examples¶

src/main/java/nitin/exceptionHandling
src/main/java/nitin/io/fileIO/readfiles1/AllPalindromes.java
src/main/java/nitin/io/fileIO/readfiles2/FileUtils.java