静态vs。Java中的动态绑定

Question

public static void callEat(Animal animal) {
    System.out.println("Animal is eating");
}

public static void callEat(Dog dog) {
    System.out.println("Dog is eating");
}

public static void main(String args[])
{
    Animal a = new Dog();
    callEat(a);
}

Answer 1

来自JavaRevited博客文章：

以下是静态绑定和动态绑定之间的几个重要区别：

1. Java中的静态绑定发生在编译时，而动态绑定发生在运行时。
2. private、final和static方法和变量使用静态绑定并由编译器绑定，而虚方法在运行时基于运行时对象绑定。
3. 静态绑定使用type(Java中的class)信息进行绑定，而动态绑定使用object解析绑定。
4. 重载方法使用静态绑定绑定，而重写方法在运行时使用动态绑定绑定。

public class StaticBindingTest {  
    public static void main(String args[]) {
        Collection c = new HashSet();
        StaticBindingTest et = new StaticBindingTest();
        et.sort(c);
    }
    //overloaded method takes Collection argument
    public Collection sort(Collection c) {
        System.out.println("Inside Collection sort method");
        return c;
    }
    //another overloaded method which takes HashSet argument which is sub class
    public Collection sort(HashSet hs) {
        System.out.println("Inside HashSet sort method");
        return hs;
    }
}

输出：内部集合排序方法

Java中的动态绑定示例

public class DynamicBindingTest {   
    public static void main(String args[]) {
        Vehicle vehicle = new Car(); //here Type is vehicle but object will be Car
        vehicle.start(); //Car's start called because start() is overridden method
    }
}

class Vehicle {
    public void start() {
        System.out.println("Inside start method of Vehicle");
    }
}

class Car extends Vehicle {
    @Override
    public void start() {
        System.out.println("Inside start method of Car");
    }
}

输出：车内启动方法