16. Interface Evolution: Private & Static Methods

Scenario

Interfaces are no longer just for abstract methods. Since Java 8 and 9, they can have logic. This demonstrates how to use static and private methods in interfaces.

Code Block

interface Logger {
    default void logInfo(String msg) {
        log(msg, "INFO");
    }

    default void logError(String msg) {
        log(msg, "ERROR");
    }

    // Private method for internal logic (Java 9+)
    private void log(String msg, String level) {
        System.out.println("[" + level + "] " + msg);
    }

    // Static method for utility (Java 8+)
    static void printHeader() {
        System.out.println("=== SYSTEM LOGS ===");
    }
}

class ConsoleLogger implements Logger {}

public class Main {
    public static void main(String[] args) {
        Logger.printHeader(); // Called on Interface
        ConsoleLogger cl = new ConsoleLogger();
        cl.logInfo("System Started");
        cl.logError("Memory Low");
    }
}

Take Your Shot

Predicted Output

Type exactly what you think will be printed in the console.