public class wrapperclass {

public List<account> acc {get;set;}
public List<contact> con {get;set;}
public account a {get;set;}
public boolean b {get;set;}


public list<wrapper> wrap=new List<wrapper>();

public list<wrapper> getContacts(){

String accid=ApexPages.currentPage().getParameters().get('id');
a=[select id,name from account where id=:accid];
con=[select id,name,email from contact where accountid=:accid];
    if(con.size()!=0)
    {
        b=true;
    }
    else
    {
        b=false;
    }
 for(Contact c:con)
 {
     wrap.add(new wrapper(c.id,c.name,c.email));
 }
return wrap;
}

<apex:page controller="wrapperclass">
<apex:pageBlock>
    <apex:pageBlockTable  value="{!Contacts}" var="w" rendered="{!b}">
        <apex:column headerValue="Related Contacts"/>
        <apex:column headerValue="{!a.name}"/>
        <apex:column value="{!w.id}"/>
        <apex:column value="{!w.name}"/>
        <apex:column value="{!w.email}"/>

    </apex:pageBlockTable>