javademos/sealed/broken/VisitorAdded.java

public class VisitorAdded {
    interface Payment { <R> R accept(Visitor<R> v); }
    interface Visitor<R> { R visitCard(Card c); R visitUpi(Upi u); R visitWallet(Wallet w); }   // Wallet added here
    record Card() implements Payment { public <R> R accept(Visitor<R> v) { return v.visitCard(this); } }
    record Upi() implements Payment { public <R> R accept(Visitor<R> v) { return v.visitUpi(this); } }
    record Wallet() implements Payment { public <R> R accept(Visitor<R> v) { return v.visitWallet(this); } }

    // Two existing operations, neither knows about Wallet: each one now fails to compile.
    static class Fee implements Visitor<Long> {
        public Long visitCard(Card c) { return 2L; }
        public Long visitUpi(Upi u) { return 0L; }
    }
    static class Label implements Visitor<String> {
        public String visitCard(Card c) { return "card"; }
        public String visitUpi(Upi u) { return "upi"; }
    }
}