jQuery循环判断点击某节点

<div class="three_ad_container"> 
 <div class="main_ad_container"><img src="/images/insurance/3lianad.jpg" /></div> 
 <div class="left_tree_ad_btn_container"> 
     <ul> 
  <li class="tree_ad_btn_bg"><img src="/images/insurance/3lianad_small.jpg" /></li> 
     </ul> 
     <ul> 
  <li class="tree_ad_btn_bg have_bg"><img src="/images/insurance/3lianad_small.jpg" /></li> 
     </ul> 
     <ul> 
  <li class="tree_ad_btn_bg"><img src="/images/insurance/3lianad_small.jpg" /></li> 
     </ul> 
 </div> 
    </div> 

<script>
jQuery(".left_tree_ad_btn_container > ul > li").click(function(){ 
 jQuery(".have_bg").removeClass("have_bg"); 
 var objLi = jQuery(this); 
 objLi.attr("class", "tree_ad_btn_bg have_bg"); 
 jQuery.each(jQuery(".left_tree_ad_btn_container > ul > li"), function(index, value){ 
     if(jQuery(this).attr("class") == objLi.attr("class")){ 
  alert(index); 
     // jQuery(".main_ad_container > img").attr("src", "/images/insurance/01_bg.png"); 
     } 
 }); 
    }); 
</script>