This code is error badged, though it works perfectly.

The error badge is at commented line.

public abstract class Main1 {

    abstract class M2 {
        abstract void doWork();
    }

    public static void main(String[] args) {
        Main1 m = new Main1() {
            @Override
            void doWork() {
                System.out.println("Main1 working");
            }
        };
        
        M2 m2 = m.new M2() { // this line is error badged
            @Override
            void doWork() {
                System.out.println("M2 working");
            }
        };

        m.doWork();
        m2.doWork();
    }

    abstract void doWork();

}