如何判断php复选框是否被选中

<form action ="HandleFormCheckBox.php" method="post">

<ul>

 <li><input type ="checkbox" name ="category[]" value ="php">php教程</li>

 <li><input type ="checkbox" name ="category[]" value ="java">java教程</li>

 <li><input type ="checkbox" name ="category[]" value ="mysql">mysql教程</li>

 <li><input type ="checkbox" name ="category[]" value ="html">html教程</li>

</ul>

<input type ="submit">

</form>

<?php

$checkbox_select=$_POST["category"];

print_r($checkbox_select);

?>

Array( [0]='php' [1]='java' )

<?php

$checkbox_select=$_POST["category"];

for($i=0;$i<count($checkbox_select);$i++)

{

echo "选项".$checkbox_select[$i]."被选中<br />";

}

?>