Find the error in this code snippet:

Find the error in this code snippet:

abstract class Machine {
    abstract void operate();
    void start() {
        System.out.println("Machine started");
    }
}
class Printer extends Machine {
    void operate() {
        System.out.println("Printing");
    }
    void start() {
        System.out.println("Printer started");
    }
}
public class Test {
    public static void main(String[] args) {
        Machine m = new Printer();
        m.start();
    }
}