isAssignableFrom 是用来判断一个类Class1和另一个类Class2是否相同或是另一个类的超类或接口。
通常调用格式是
Class1.isAssignableFrom (Class2)
调用者和参数都是 java.lang.Class 类型。

简单例子

public class A {

}
public class B extends A {

}

测试

/**Class.isAssignableFrom
 * isAssignableFrom 是用来判断一个类Class1和另一个类Class2是否相同或是另一个类的超类或接口。 
 * @author 刘楠
 *
 */
public class Test2 {

    public static void main(String[] args) {
        A a = new A();
        B b = new B();
        A ba = new B();
        System.out.println(a.getClass());
        System.out.println(b.getClass());
        System.out.println(ba.getClass());
        System.out.println("=====================");
        System.out.println(a.getClass().isAssignableFrom(b.getClass()));//true
        System.out.println(b.getClass().isAssignableFrom(a.getClass()));//false
        System.out.println("=====================");
        System.out.println(ba.getClass().isAssignableFrom(a.getClass()));//false
        System.out.println(a.getClass().isAssignableFrom(ba.getClass()));//true
        System.out.println("=====================");
        System.out.println(ba.getClass().isAssignableFrom(b.getClass()));//true
        
        System.out.println(b.getClass().isAssignableFrom(ba.getClass()));//true
        
        
        System.out.println("1-------------");
        System.out.println(A.class.isAssignableFrom(a.getClass()));//true
        System.out.println(B.class.isAssignableFrom(b.getClass()));//true
        System.out.println(A.class.isAssignableFrom(b.getClass()));//true
        System.out.println(B.class.isAssignableFrom(a.getClass()));//false
        System.out.println(A.class.isAssignableFrom(ba.getClass()));//true
        System.out.println(B.class.isAssignableFrom(ba.getClass()));//true
        
        System.out.println("2-------------");
        System.out.println(a.getClass().isAssignableFrom(A.class));//true
        System.out.println(b.getClass().isAssignableFrom(B.class));//true
        System.out.println(a.getClass().isAssignableFrom(B.class));//true
        System.out.println(b.getClass().isAssignableFrom(A.class));//false
        System.out.println(ba.getClass().isAssignableFrom(A.class));//false
        System.out.println(ba.getClass().isAssignableFrom(B.class));//true
        
        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));//string false
        System.out.println("abc".getClass().isAssignableFrom(Object.class));//string false
    }

结果

class com.ghgcn.test01.A
class com.ghgcn.test01.B
class com.ghgcn.test01.B
=====================
true
false
=====================
false
true
=====================
true
true
1-------------
true
true
true
false
true
true
2-------------
true
true
true
false
false
true
3-------------
true
true
4-------------
false
false