Log example. Teaching my little brother some programming ;-)

Logger.java

public abstract class AbstractLogger {
    public abstract void log(String message);
}

public interface Logger {
    void log(String message);
}

public interface UserLogger {
    void log(User user, String message);
}

public class FileLogger extends AbstractLogger {
    private File file;

    public Logger(File file) {
        this.file = file;
    }

    public void log(String message) {
        file.write(message);
    }
        
}

public class PrintLogger implements Logger, UserLogger {

    public void log(String message) {
        System.out.println(message);
    }

    public void log(User user, String message) {
        // ...
    }

    public void somethingRararara() {
        // ...
    }
        
}

public class MyProgram {
    public static void main(String[] args) {
        Logger logger = new PrintLogger();
        doSomething(logger);
    }
    private static doSomething(Logger logger) {
        logger.log("Hello, you man!");
    }
}

Ser bra ut

Tack! 👍