android - Determine phone is rooted -

i trying create app check phone rooted or not, have follow few example, still cant work, please 1 me , or maybe give more example. wondering if there better achieve in recent releases?

import java.io.file;   import android.app.alertdialog; import android.content.dialoginterface; import android.support.v7.app.actionbaractivity;  public class mainactivity extends actionbaractivity {           public boolean isphonerooted() {                // check if /system/app/superuser.apk present             try {               file file = new file("/system/app/superuser.apk");               if (file.exists()) {                    new alertdialog.builder(this)                      .seticon(r.drawable.ic_launcher)                      .settitle("phone rooted")                      .setpositivebutton("ok",                         new dialoginterface.onclicklistener() {                              @override                         public void onclick(dialoginterface dialog, int which) {                          // todo auto-generated method stub                         }                        }).show();                }               else{                   new alertdialog.builder(this)                      .seticon(r.drawable.ic_launcher)                      .settitle("phone no rooted")                      .setpositivebutton("ok",                         new dialoginterface.onclicklistener() {                              @override                         public void onclick(dialoginterface dialog, int which) {                          // todo auto-generated method stub                        }                       }).show();               }             } catch (throwable e1) {               // ignore             }             return false;           } }