Mark fields private so other classes cannot assign them directly. Offer a method when a change is allowed. That method can reject a blank name or a negative mark before the object stores it.
A getter returns the value. A setter changes it. You do not need a setter for a value that should stay fixed after the constructor, such as an id.
Example
name() returns the private field. main never touches the field directly.
public class Trainee {
private String name;
Trainee(String name) { this.name = name; }
String name() { return name; }
public static void main(String[] args) {
Trainee t = new Trainee("Karthik");
System.out.println(t.name());
}
}private stops t.name = "" from another class. The only way in is the constructor or a method you wrote. That is the point of the restriction.
