hi this is zuber
this is the visual page code and controller class return by me
and i am not getting associated contacts what mistake i did here please help to get my mistake
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<apex:page sidebar="false" controller="getrelatedcontacts" action="{!getaccounts}">
<apex:sectionHeader title="contacts of accounts"/>
<apex:form >
<apex:pageBlock >
<apex:actionRegion >
<apex:selectList size="1" multiselect="false" label="Account" value="{!selectedid}">
<apex:selectOptions value="{!listoptions}">
<apex:actionSupport event="onchange" action="{!getcontacts}" reRender="aj"/>
</apex:selectOptions>
</apex:selectList>
</apex:actionRegion>
<apex:pageBlockTable value="{!listcontact}" var="a" id="aj">
<apex:column headerValue="first name" value="{!a.firstname}"/>
<apex:column headerValue="second name" value="{!a.lastname}"/>
<apex:column headerValue="phone" value="{!a.phone}"/>
</apex:pageBlockTable>
</apex:pageBlock>
</apex:form>
</apex:page>
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public class getrelatedcontacts 
{
Public list<selectoption> listoptions{get;set;}
Public list<contact> listcontact{get;set;}
Public string selectedid{get;set;}

Public void getaccounts()
{
list<account> listaccounts = [select id, name from account order by name];
if(!listaccounts.isempty())
{
listoptions = new list<selectoption>();
for(account acc: listaccounts)
{
listoptions.add(new selectoption(acc.id, acc.name));
}
}
}
Public void getcontacts()
{
listcontact = new list<contact>();
listcontact = [select id, firstname, lastname, phone from contact where accountid =: selectedid];
}
}