Method hiding là gì? Khác method overriding thế nào?

Method hiding xảy ra khi subclass khai báo static method trùng signature parent → không override mà che giấu.

JVM dispatch theo kiểu reference (compile-time).

class Parent {
  static void who() { System.out.println("Parent"); }
  void instanceWho() { System.out.println("Parent"); }
}
class Child extends Parent {
  static void who() { System.out.println("Child"); }
  @Override void instanceWho() { System.out.println("Child"); }
}

Parent p = new Child();
p.who();           // "Parent" ← HIDING, dispatch theo reference
p.instanceWho();   // "Child"  ← OVERRIDING, dispatch theo object thực

Quy tắc:
- Luôn gọi static qua tên class: Parent.who() — IDE cảnh báo nếu gọi qua instance.
- Đừng "override" static — đổi sang instance method nếu cần polymorphism.
- Field cũng "hidden" — parent.field lấy field theo reference type, không theo object.

Chỉ instance method được override (dynamic dispatch). Static/field/private/final chỉ hide được.

Method hiding happens when a subclass declares a static method with the parent's signature → not overriding, but hiding.

The JVM dispatches by reference type (compile-time).

class Parent {
  static void who() { System.out.println("Parent"); }
  void instanceWho() { System.out.println("Parent"); }
}
class Child extends Parent {
  static void who() { System.out.println("Child"); }
  @Override void instanceWho() { System.out.println("Child"); }
}

Parent p = new Child();
p.who();           // "Parent" ← HIDING, dispatched by reference
p.instanceWho();   // "Child"  ← OVERRIDING, dispatched by actual object

Rules:
- Always call statics via the class name: Parent.who() — IDEs warn when called via an instance.
- Do not "override" static — switch to instance methods if you need polymorphism.
- Fields are also "hidden" — parent.field reads by reference type, not actual object.

Only instance methods are overridden (dynamic dispatch). Statics/fields/private/final can only be hidden.