isAssignableFrom方法是native方法,它的作用是用来判断两个类的之间的关联关系,也可以说是一个类是否可以被强制转换为另外一个实例对象:
/**
* Determines if the class or interface represented by this
* {@code Class} object is either the same as, or is a superclass or
* superinterface of, the class or interface represented by the specified
* {@code Class} parameter. It returns {@code true} if so;
* otherwise it returns {@code false}. If this {@code Class}
* object represents a primitive type, this method returns
* {@code true} if the specified {@code Class} parameter is
* exactly this {@code Class} object; otherwise it returns
* {@code false}.
*
* <p> Specifically, this method tests whether the type represented by the
* specified {@code Class} parameter can be converted to the type
* represented by this {@code Class} object via an identity conversion
* or via a widening reference conversion. See <em>The Java Language
* Specification</em>, sections 5.1.1 and 5.1.4 , for details.
*
* @param cls the {@code Class} object to be checked
* @return the {@code boolean} value indicating whether objects of the
* type {@code cls} can be assigned to objects of this class
* @exception NullPointerException if the specified Class parameter is
* null.
* @since JDK1.1
*/
public native boolean isAssignableFrom(Class<?> cls);
翻译过来注释中对方法的解释就是:
有两个Class类型的类象,一个是调用isAssignableFrom方法的类对象(后称对象a),以及方法中作为参数的这个类对象(称之为对象b),这两个对象如果满足以下条件则返回true,否则返回false:
- a对象所对应类信息是b对象所对应的类信息的父类或者是父接口,简单理解即a是b的父类或接口
- a对象所对应类信息与b对象所对应的类信息相同,简单理解即a和b为同一个类或同一个接口