Java.lang.Class类中isAssignableFrom()方法具有什么功能呢？

package com.java.other;
import org.junit.Test;
public class other {
    /**
     * java265.com java.lang.Class 测试示例分享
     * 
     * @throws Exception
     * 
     */
    @Test
    public void test() throws Exception {
        A a = new A();
        B b = new B();
        Class c = a.getClass();
        Class c2 = b.getClass();
        System.out.println(c.isAssignableFrom(c2));
    }
    public class A {
    }

    public class B extends A {
    }
}
-------运行以上代码，将输出以下信息-----
true