Class中isAssignableFrom() 方法

看Spring源码的时候看到这个方法：

    protected WebApplicationContext createWebApplicationContext(ServletContext sc) {
        Class<?> contextClass = determineContextClass(sc);
        if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
            throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
                    "] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]");
        }
        return (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
    }

第一次见到第三行中的用法，点开看了下，原文是这么说的：

Determines if the class or interface represented by this Class object is either the same as, or is a superclass or superinterface of, the class or interface represented by the specified Class parameter. 
It returns true if so; otherwise it returns false. 
If this Class object represents a primitive type, this method returns true if the specified Class parameter is exactly this Class object; otherwise it returns false. 

Specifically, this method tests whether the type represented by the specified Class parameter can be converted to the type represented by this Class object via an identity conversion or via a widening reference conversion. 
See The Java Language Specification, sections 5.1.1 and 5.1.4 , for details.

就是说判断一个类是否另一个类或接口的子类。

例如

A.class.isAssignableFrom(B.class)

这句就是判断 B是否A的父接口或者父类。

顺手搜了下，得到一个小惊喜：

instanceof, isinstance,isAssignableFrom的区别