java中isAssignableFrom()方法与instanceof关键字的区别

一、isAssignableFrom()方法与instanceof关键字的区别

• isAssignableFrom()方法是从类继承的角度去判断。

  父类.class.isAssignableFrom(子类.class)
  

• instanceof关键字是从实例继承的角度去判断。

  子类 子类实例= new 子类(); 
  子类实例 instanceof 父类类型
  

• isAssignableFrom()方法是判断是否为某个类的父类，instanceof关键字是判断是否某个类的子类。

二、isAssignableFrom()方法与instanceof关键字的使用方法

• isAssignableFrom()方法的调用者和参数都是Class对象，调用者为父类，参数为本身或者其子类。
• instanceof关键字两个参数，前一个为类的实例，后一个为其本身或者父类的类型。

三、isAssignableFrom()方法与instanceof关键字具体示例

1、代码

public interface EveryThing {
    public abstract void alive();
}

public class Animal implements EveryThing{
    @Override
    public void alive() {
        System.out.println("动物是有活力的");
    }

    public void eat(){
        System.out.println("动物吃食物");
    }

    public void sleep(){
        System.out.println("动物睡觉");
    }
}

public class Dog extends Animal{
    public void play(){
        System.out.println("狗可以跑");
    }
}

public class Test {
    public static void main(String[] args) {
        Animal animal = new Animal();
        Dog dog = new Dog();
        /** 类测试 */
        System.out.println("Dog.class.isAssignableFrom(Animal.class) = "+Dog.class.isAssignableFrom(Animal.class));
        System.out.println("Animal.class.isAssignableFrom(Dog.class) = "+Animal.class.isAssignableFrom(Dog.class));
        System.out.println("animal instanceof Animal = "+(animal instanceof Animal));
        System.out.println("dog instanceof Animal ="+(dog instanceof Animal));
        System.out.println("animal instanceof Dog = "+(animal instanceof Dog));
        System.out.println("dog instanceof Dog = "+(dog instanceof Dog));

       /* 接口测试*/
        System.out.println("EveryThing.class.isAssignableFrom(Animal.class) = "+EveryThing.class.isAssignableFrom(Animal.class));
        System.out.println("Animal.class.isAssignableFrom(EveryThing.class) = "+Animal.class.isAssignableFrom(EveryThing.class));
        System.out.println("animal instanceof EveryThing = "+(animal instanceof EveryThing));
    }
}

2、运行main函数，输出结果如下：