在判断一个实例引用的类型时，使用的是实际类型，而不是声明的类型。
class Vehicle {}
public class Car extends Vehicle {
public static void main(String args[]){
Car c1 = new Car();
Vehicle v2 = new Car(); // v2 是 Car 类型
Vehicle v3 = new Vehicle();
//Car 是 Vehicle类型, Vehicle 不是 Car 类型
boolean result1 = c1 instanceof Vehicle; // true
boolean result2 = v2 instanceof Car; // true
boolean result3 = v2 instanceof Vehicle; // true
boolean result4 = v3 instanceof Car; // false
System.out.println(result1);
System.out.println(result2);
System.out.println(result3);
System.out.println(result4);
}
}
