如何用java读取lucene 4.0索引？(How to read lucene 4.0 index with java?)

 第二种选择是完全有效和良好的做法，但第一种选择毫无意义。 您正在尝试jQueryify一个已经jQueryified的对象。 它基本上就像$($("body")) 。 
 
 另请注意，将$到包含jQuery对象的变量是一个好习惯。 您的代码应如下所示： 
 
var $myElement2 = $(".container").find('ul li:eq(2)');
$myElement2.css('background', 'blue');
 
 正如@Terry所写，最优化的方式是： 
 
var $c = $(".container ul li");
var $second = $c.eq(2);

The second option is completely valid and good practice, however the first makes no sense. You're trying to jQueryify an object which has already been jQueryified. It basically is something like $($("body")).
 
Also note that it's good practice to prepend $ to variables which contains jQuery object. Your code should look like this:
 
var $myElement2 = $(".container").find('ul li:eq(2)');
$myElement2.css('background', 'blue');
 
As @Terry wrote, the most optimized way would be:
 
var $c = $(".container ul li");
var $second = $c.eq(2);