Groovy:this.metaClass与instance.metaClass相对应

我在书中遇到了下面的groovy脚本代码.它给我带来了一些奇怪的输出.

class Person{
  def work(){
    println "work()"
  }
  def sports=['basketball','football','voleyball']
  def methodMissing(String name, args){
    if(name in sports){
        println "injected ${name} into Person class"
        Person instance=this
        println "this.metaClass:\t\t${this.metaClass}"
        println "instance.metaClass:\t${instance.metaClass}"
        assert this.metaClass==instance.metaClass
    }else{
        println "no such method:${name}() in Person class"
    }
  }
}
def jack=new Person()
jack.football()

它的输出如下:

injected football into Person class
this.metaClass:     groovy.lang.MetaClassImpl@245b4bdc[class Person]
instance.metaClass: org.codehaus.groovy.runtime.HandleMetaClass@245b4bdc[groovy.lang.MetaClassImpl@245b4bdc[class Person]]
Caught: Assertion failed: 
//I did not paste the detailed assertion here for simplicity

所以我很困惑:

为什么this.metaClass不等于instance.metaClass？

更进一步,我不能使用this.metaClass来注入新方法; groovy告诉我this.metaClass没有这样的属性,我打算注入.

"org.codehaus.groovy.runtime.HandleMetaClass@245b4bdc [groovy.lang.MetaClassImpl@245b4bdc [class Person]]"是什么意思？我知道"245b4bdc"可能是对象指针.但是为什么HandleMetaClass和MetaClassImpl具有相同的指针值"245b4bdc"？

目前,我发现@ 245b4bdc不是" 对象引用 ",因此HandleMetaClass @ 245b4bdc不一定与MetaClassImpl @ 245b4bdc相同.我们可以使用Object.is()方法来判断它们是否相同.(我这样做,结果是假的)