// Extension method 第一个参数必须与当前对象的类型一致，在调用时会将当前对象自身传给扩展方法的第一个参数
if (targetClass != extensionMethodParaTypes[0]) {
	throw new RuntimeException(buildMethodSignatureForException("The first argument type of : " + extensionClass.getName() + ".", methodName, extensionMethodParaTypes) + " must be: " + targetClass.getName());
}

if (!extensionMethodParaTypes[0].isAssignableFrom(targetClass)) {
	throw new RuntimeException(buildMethodSignatureForException("The first argument type of : " + extensionClass.getName() + ".", methodName, extensionMethodParaTypes) + " must be: " + targetClass.getName());
}

class NumberExt {
    public String format(Number target, String pattern){
       //do something
    }
}