How jQuery modifies the style under li and the src value of img under li_jquery

How jQuery modifies the style under li and the src value of img under li. The following is the specific implementation code. Friends who need it can take a look

$(".test li").click(function() {
$(".test li a").removeClass("test01");
$(".test li a").addClass("test02");
$("a", this).removeClass("test02");//当前li中的a标签
$("a", this).addClass("test01");
var title_index = $(this).index();//当前li的index
//li中所有的img
var allImg = $(".test li img");
for ( var i = 0; i < allImg.size(); i++) {
if (i % 2 == 0) {
$(allImg[i]).attr("src", "images/b04.gif");//改变img的src
} else {

$(allImg[i]).attr("src", "images/b05.gif");
}
}
//当前li中的img
var imgs = $("img", this);
for ( var i = 0; i < imgs.size(); i++) {
if (i == 0) {
$(imgs[i]).attr("src", "images/b01.gif");
} else {

$(imgs[i]).attr("src", "images/b02.gif");
}

}
if (title_index == 0) {
$("#a).hide();
$("#b").show();
} else {
$("#b").hide();
$("#a").show();
} 
})