JAVA多态的底层实现机制解析(最新推荐)

Animal a = new Dog();
a.run();  // 调用 Dog.run()

Animal vtable:
----------------
0x01 → run()   // Animal.run
0x02 → eat()
Dog vtable:
----------------
0x05 → run()   // Dog.run 覆盖掉 Animal.run
0x02 → eat()   // 继承父类方法

Animal a = new Dog();
a.run(); // JVM：查找 a 的实际类型 Dog 的 vtable → 入口 0x05

class Animal {
    void run() { System.out.println("Animal run"); }
}
class Dog extends Animal {
    @Override
    void run() { System.out.println("Dog run"); }
}

0: aload_1
1: invokevirtual #5 <Animal.run>

public class OverloadDemo {
    void test(Object o) { System.out.println("Object"); }
    void test(String s) { System.out.println("String"); }
    public static void main(String[] args) {
        OverloadDemo demo = new OverloadDemo();
        Object o = "hello";
        demo.test(o); // 输出：Object   （编译期决定）
    }
}

class A { void hello() { System.out.println("A"); } }
class B extends A { @Override void hello() { System.out.println("B"); } }
public class OverrideDemo {
    public static void main(String[] args) {
        A a = new B();
        a.hello();  // 输出：B（运行期决定）
    }
}

abstract class Vehicle {
    abstract void run();
}
class Car extends Vehicle {
    @Override
    void run() {
        System.out.println("Car is running...");
    }
}
class Bike extends Vehicle {
    @Override
    void run() {
        System.out.println("Bike is running...");
    }
}
public class PolymorphismDemo {
    public static void main(String[] args) {
        Vehicle v1 = new Car();
        Vehicle v2 = new Bike();
        show(v1);
        show(v2);
    }
    static void show(Vehicle v) {
        v.run();  // 动态分派，查找实际对象类型
    }
}