class1.isAssignableFrom(class2) 判定此 Class 對象所表示的類或接口與指定的 Class 參數所表示的類或接口是否相同，或是否是其超類或超接口。如果是則返回 true；否則返回 false。如果該 Class表示一個基本類型，且指定的 Class 參數正是該 Class 對象，則該方法返回 true；否則返回 false。

1.class2是不是class1的子類或者子接口

2.Object是所有類的父類

一個例子搞定：

package com.auuzee.test1;

class A {
}

class B extends A {
}

public class Test1 {
    public static void main(String[] args) {

        A a = new A();
        B b = new B();
        A ba = new B();
        System.out.println("1-------------");
        System.out.println(A.class.isAssignableFrom(a.getClass()));
        System.out.println(B.class.isAssignableFrom(b.getClass()));
        System.out.println(A.class.isAssignableFrom(b.getClass()));
        System.out.println(B.class.isAssignableFrom(a.getClass()));
        System.out.println(A.class.isAssignableFrom(ba.getClass()));
        System.out.println(B.class.isAssignableFrom(ba.getClass()));
        System.out.println("2-------------");
        System.out.println(a.getClass().isAssignableFrom(A.class));
        System.out.println(b.getClass().isAssignableFrom(B.class));
        System.out.println(a.getClass().isAssignableFrom(B.class));
        System.out.println(b.getClass().isAssignableFrom(A.class));
        System.out.println(ba.getClass().isAssignableFrom(A.class));
        System.out.println(ba.getClass().isAssignableFrom(B.class));
        System.out.println("3-------------");
        System.out.println(Object.class.isAssignableFrom(b.getClass()));
        System.out.println(Object.class.isAssignableFrom("abc".getClass()));
        System.out.println("4-------------");
        System.out.println("a".getClass().isAssignableFrom(Object.class));
        System.out.println("abc".getClass().isAssignableFrom(Object.class));
    }
}

 

 參考鏈接：https://www.cnblogs.com/greatfish/p/6097507.html