asset dependcy problem

Yii 2.0 General Discussions
1 

    public $js = [

        'js/main.js',

    ];

    public $depends = [

        'yii\web\YiiAsset',

        'yii\web\JqueryAsset',

        'yii\bootstrap\BootstrapAsset',

    ];

turns out to be


<script src="/assets/5cb2078/jquery.js"></script>

<script src="/assets/800ac150/yii.js"></script>

<script src="/assets/800ac150/yii.gridView.js"></script>

<script src="/js/main.js"></script>

<script src="/assets/27354a12/js/bootstrap.js"></script>

<script src="/assets/520e15d2/js/dropdown-x.js"></script>

why is this so, i want my main.js after bootstrap.js, and set the dependency, but seem not working.