カスタマイズオブジェクトを取得

Apex Class:XNShowObjectCtl.cls
public with sharing class XNShowObjectCtl {
 public String objName{get;set;}
 public List<SelectOption> getObjNames(){
  List<SelectOption> options = new List<SelectOption>();  
    Map<String, Schema.SObjectType> gd = Schema.getGlobalDescribe();
    for (Schema.SObjectType st : gd.values()) {
     Schema.DescribeSObjectResult r = st.getDescribe();
     if(r.isCustom() && r.isQueryable()){
       options.add(new SelectOption(r.getName(), r.getLabel()));
     }
    }
  return options;
 }
}

VF Page:XNShowObject.page

<apex:page controller="XNShowObjectCtl" showHeader="true" sidebar="false" >
 <apex:form >
   <apex:selectList value="{!objName}" size="10" multiselect="false">
       <apex:selectOptions value="{!ObjNames}"/>
   </apex:selectList>
  </apex:form>
</apex:page>