JavaHai khái niệm dễ nhầm — cùng chữ "over" nhưng giải quyết bài toán khác hẳn.
| Overloading | Overriding | |
|---|---|---|
| Scope | Cùng class | Subclass override method của parent |
| Signature | Khác tham số | Trùng signature với parent |
| Resolution | Compile-time | Runtime (dynamic dispatch) |
| Polymorphism | Static | Dynamic (subtype) |
java
class Calculator {
int add(int a, int b) { return a + b; } // overload
double add(double a, double b) { return a + b; } // overload
}
class Animal { void speak() { System.out.println("..."); } }
class Dog extends Animal {
@Override void speak() { System.out.println("Woof"); } // override
}
Animal a = new Dog();
a.speak(); // "Woof" — dispatch theo kiểu THỰC của objectQuy tắc override: access không được hẹp hơn parent, không throw checked exception rộng hơn, luôn dùng @Override.
Easy to confuse — both start with "over" but they solve different problems.
| Overloading | Overriding | |
|---|---|---|
| Scope | Same class | Subclass redefines parent's method |
| Signature | Different parameters | Same signature as parent |
| Resolution | Compile-time | Runtime (dynamic dispatch) |
| Polymorphism | Static | Dynamic (subtype) |
java
class Calculator {
int add(int a, int b) { return a + b; } // overload
double add(double a, double b) { return a + b; } // overload
}
class Animal { void speak() { System.out.println("..."); } }
class Dog extends Animal {
@Override void speak() { System.out.println("Woof"); } // override
}
Animal a = new Dog();
a.speak(); // "Woof" — dispatched by the ACTUAL object typeOverriding rules: access cannot be narrower than parent, cannot throw broader checked exceptions, always use @Override.