Properties: get and set

public class EventTicket {
    public Decimal price;
}

EventTicket ticket = new EventTicket();
ticket.price = -500; // perfectly legal, but nonsensical

1. public class EventTicket { — a plain class with a plain field.
2. public Decimal price; — nothing stops this field from holding a value that makes no business sense.
3. } — closes the class.
4. (blank line)
5. EventTicket ticket = new EventTicket(); — creates a ticket.
6. ticket.price = -500; — a negative ticket price shouldn't be allowed, but a plain field has no way to say so — this compiles and runs without complaint.

public class EventTicket {
    public Decimal price {
        get { return price; }
        set {
            if (value < 0) {
                price = 0;
            } else {
                price = value;
            }
        }
    }
}

EventTicket ticket = new EventTicket();
ticket.price = -500;
System.debug(ticket.price); // 0, not -500

1. public class EventTicket { — the class.
2. public Decimal price { — this is now a property, not a plain field — it looks the same from the outside but runs code behind the scenes.
3. get { return price; } — runs whenever the property is read.
4. set { — runs whenever the property is written.
5. if (value < 0) { — value is a built-in keyword holding the incoming value being assigned.
6. price = 0; — invalid input gets corrected before it's ever stored.
7. } else { — otherwise…
8. price = value; — …the value is stored as given.
9. } — closes the else.
10. } — closes set.
11. } — closes the property.
12. } — closes the class.
13. (blank line)
14. EventTicket ticket = new EventTicket(); — creates a ticket.
15. ticket.price = -500; — the syntax looks identical to setting a plain field, but this now runs through the set block above.
16. System.debug(ticket.price); — logs 0, not -500 — the invalid value was caught and corrected.

public class EventTicket {
    public String eventName { get; set; }
}

1. public class EventTicket { — the class.
2. public String eventName { get; set; } — when no custom logic is needed, { get; set; } is shorthand for a property with default get/set behavior — functionally similar to a public field, but written in a way that leaves room to add real validation later without changing how callers use it.
3. } — closes the class.