https://qooah.com/2012/06/08/%e9%a3%9f%e5%93%81%e5%ae%89%e5%85%a8%e9%9f%bf%e8%ad%a6%e8%99%9f-android-%e7%89%88-%e4%b8%ad%e5%9c%8b%e6%b1%82%e7%94%9f%e6%89%8b%e5%86%8a-%e5%85%8d%e8%b2%bb%e4%b8%8b%e8%bc%89/