一文搞懂java中getClass(),instanceof,isAssignableFrom()区别

最新推荐文章于 2023-02-28 13:49:41 发布

原创最新推荐文章于 2023-02-28 13:49:41 发布 · 440 阅读

1 ·

CC 4.0 BY-SA版权

Java 专栏收录该内容

13 篇文章

订阅专栏

java----getClass(),instanceof,isAssignableFrom()区别

结论

getClass()	instanceof	isAssignableFrom（）
获取类	判断是否实例	判断是否可转化
相同的类返回true	相同的类，子类，实现类都可以返回true	父类.isAssignableFrom(子类)返回true

isAssignableFrom()方法与instanceof关键字的区别总结为以下两个点：

isAssignableFrom()方法是从类继承的角度去判断，instanceof关键字是从实例继承的角度去判断。
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。

上代码

public interface SomeInterface {
}

public class Father implements SomeInterface{
}

public class Child extends Father{
}

getClass()

	public static void main(String[] args) {
        Child child = new Child();
        Father father = new Father();
        testGetClass(father);
        testGetClass(child);
    }
    public static void testGetClass(Object o){
        log.info("o.getClass Father:{}",o.getClass()==Father.class);
        log.info("o.getClass Child:{}",o.getClass()==Child.class);
    }

结果

19:36:04.616 [main] INFO  - o.getClass Father:true
19:36:04.619 [main] INFO  - o.getClass Child:false
19:36:04.619 [main] INFO  - o.getClass Father:false
19:36:04.619 [main] INFO  - o.getClass Child:true

结论getClass()必须是相同的类

instanceof

	public static void main(String[] args) {
        Child child = new Child();
        Father father = new Father();
        testInstanceOf(father);
        testInstanceOf(child);
	}
	/**
     * 判断是类型的实例，包括实现类
     * @param o
     */
    public static void testInstanceOf(Object o){
        log.info("o instanceof Father:{}",o instanceof Father);
        log.info("o instanceof Child:{}",o instanceof Child);
        log.info("o instanceof SomeInterface:{}",o instanceof SomeInterface);
    }

结果

19:36:04.619 [main] INFO  - o instanceof Father:true
19:36:04.619 [main] INFO  - o instanceof Child:false
19:36:04.619 [main] INFO  - o instanceof SomeInterface:true
19:36:04.619 [main] INFO  - o instanceof Father:true
19:36:04.619 [main] INFO  - o instanceof Child:true
19:36:04.619 [main] INFO  - o instanceof SomeInterface:true

结论instanceof可以是同一个类，子类或实现类

isAssignableFrom()

	public static void main(String[] args) {
        Child child = new Child();
        Father father = new Father();
        testIsAssignableFrom(father);
        testIsAssignableFrom(child);
    }
    /**
     * 父类 isAssignableFrom 子类
     * @param o
     */
    public static void testIsAssignableFrom(Object o){
        log.info("Father.class.isAssignableFrom:{}",Father.class.isAssignableFrom(o.getClass()));
        log.info("Child.class.isAssignableFrom:{}",Child.class.isAssignableFrom(o.getClass()));
        log.info("SomeInterface.class.isAssignableFrom:{}",SomeInterface.class.isAssignableFrom(o.getClass()));


        log.info("isAssignableFrom Father: {}",o.getClass().isAssignableFrom(Father.class));
        log.info("isAssignableFrom Child: {}",o.getClass().isAssignableFrom(Child.class));
        log.info("isAssignableFrom SomeInterface: {}",o.getClass().isAssignableFrom(SomeInterface.class));
    }

结果

19:36:04.619 [main] INFO  - Father.class.isAssignableFrom:true
19:36:04.619 [main] INFO  - Child.class.isAssignableFrom:false
19:36:04.619 [main] INFO  - SomeInterface.class.isAssignableFrom:true
19:36:04.619 [main] INFO  - isAssignableFrom Father: true
19:36:04.619 [main] INFO  - isAssignableFrom Child: true
19:36:04.619 [main] INFO  - isAssignableFrom SomeInterface: false


19:36:04.619 [main] INFO  - Father.class.isAssignableFrom:true
19:36:04.619 [main] INFO  - Child.class.isAssignableFrom:true
19:36:04.619 [main] INFO  - SomeInterface.class.isAssignableFrom:true
19:36:04.619 [main] INFO  - isAssignableFrom Father: false
19:36:04.619 [main] INFO  - isAssignableFrom Child: true
19:36:04.619 [main] INFO  - isAssignableFrom SomeInterface: false

结论isAssignableFrom()必须父类 isAssignableFrom() 子类