How to get app install time from android

Question

i try some method,but not success,help me.

Answer 1

PackageManager pm = context.getPackageManager();
ApplicationInfo appInfo = pm.getApplicationInfo("app.package.name", 0);
String appFile = appInfo.sourceDir;
long installed = File(appFile).lastModified();

Answer 2

I don't understand the answer -- it provides the last modified date of the App's directory. Why is that necessarily the same as the original install time of the app?