case expressions must be constant expressions问题

private int DIALOG_ALERT_DISMISS = 0;
???
??? private Handler mhandler = new Handler() {
??????? public void handleMessage(Message msg) {
??????????? switch (msg.what) {
??????????? case DIALOG_ALERT_DISMISS:

??????????????? alertDialog.dismiss();
???????????????
??????????????? break;
??????????? }

??????? }
??? };

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这样作有什么错呢，case那行报错了：case expressions must be constant expressions

?

好像是没把DIALOG_ALERT_DISMISS定义成final类型的，那么这是为什么呢？

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希望高手帮我分析分析。