String str = "/XXXX.apk";
String fileName = Environment.getExternalStorageDirectory() + str;
Intent intent = new Intent(Intent.ACTION_VIEW);
intent.setDataAndType(Uri.fromFile(new File(fileName)), "application/vnd.android.package-archive");
startActivity(intent);
卸载：
Uri packageURI = Uri.parse("package:com.demo.XXXX");
Intent uninstallIntent = new Intent(Intent.ACTION_DELETE, packageURI);
startActivity(uninstallIntent);
Environment拥有一些可以获取环境变量的方法
，package:com.demo.XXXX这个形式是 package:程序完整的路径 (包名+程序名)。
