Greeter2.java

public abstract class Greeter {
    public final void greeting() {
        waveHello();
        doHello();
        waveGoodbye();
        doGoodbye();
    }

    public void waveHello() {
        System.out.println("🙌");
    }

    public abstract void doHello();

    public void waveGoodbye() {
        System.out.println("👋️");
    }

    public abstract void doGoodbye();
}