S4中initialize函数和对象检查的运行顺序问题

请问在S4中，initialize函数和对象检查机制（validity）的运行顺序是什么？举一个例子说明我的疑问：

<br />
# definition of "testClass"<br />
setClass(<br />
         Class = "testClass",<br />
         representation = representation(Nor = "numeric", Con = "character"),<br />
         validity = function(object){<br />
           if (length(object@Nor) != length(object@Con)){<br />
             stop("Hello, it is wrong!")<br />
           } else TRUE<br />
         }<br />
         )</p>
<p># initialize method for "testClass"<br />
setMethod(<br />
          f = "initialize",<br />
          signature = "testClass",<br />
          definition = function(.Object, Nor, Con){<br />
            if (!missing(Nor)){<br />
              names(Nor) <- letters[1:length(Nor)]<br />
              .Object@Nor <- Nor<br />
              .Object@Con <- Con<br />
            }<br />
            return(.Object)<br />
          }<br />
          )</p>
<p># a right object<br />
new("testClass", Nor = 1:5, Con = letters[1:5])<br />
## An object of class "testClass"<br />
## Slot "Nor":<br />
## a b c d e<br />
## 1 2 3 4 5 </p>
<p>## Slot "Con":<br />
## [1] "a" "b" "c" "d" "e"</p>
<p># a wrong object<br />
new("testClass", Nor = 1:3, Con = letters[1:5])<br />
## An object of class "testClass"<br />
## Slot "Nor":<br />
## a b c<br />
## 1 2 3 </p>
<p>## Slot "Con":<br />
## [1] "a" "b" "c" "d" "e"<br />

很明显，如果这样设定initialize函数，建立的对象逃过了检查。这说明使用自己设定的initialize函数，检查机制没有运行或者没有发挥作用。解决办法是设定initialize函数时，加上validObject()函数，比如：

<br />
setMethod(<br />
          f = "initialize",<br />
          signature = "testClass",<br />
          definition = function(.Object, Nor, Con){<br />
            if (!missing(Nor)){<br />
              names(Nor) <- letters[1:length(Nor)]<br />
              .Object@Nor <- Nor<br />
              .Object@Con <- Con<br />
              validObject(.Object)<br />
            }<br />
            return(.Object)<br />
          }<br />
          )</p>
<p>new("testClass", Nor = 1:3, Con = letters[1:5])<br />
## 错误于validityMethod(object) : Hello, it is wrong!<br />

</p>

当然，还有一个解决办法是使用callNextMethod()，比如：

<br />
setMethod(<br />
          f = "initialize",<br />
          signature = "testClass",<br />
          definition = function(.Object, ...){<br />
            .Object <- callNextMethod()<br />
            if (length(.Object@Nor) != 0)<br />
              names(.Object@Nor) <- letters[1:length(.Object@Nor)]<br />
            return(.Object)<br />
          }<br />
          )</p>
<p>new("testClass", Nor = 1:3, Con = letters[1:5])<br />
## 错误于validityMethod(object) : Hello, it is wrong!<br />

这时，我就感到疑惑了。因为在使用callNextMethod()函数时，调用了“默认”的initialize函数（也可能我理解错误，callNextMethod()调用的不是默认函数，而是其他。如是，请批评指正），对象检查机制正常运行。因此，为什么自己设定的intialize函数没有运行检查机制，而默认的函数却运行了。initialize函数和对象检查机制的运行顺序究竟是什么呢？
</p>