java - Cannot use this in a static context -

having problem on below coding.

new alertdialog.builder(this) 

the having error, please me have look.

import java.io.file; import android.app.alertdialog; import android.content.dialoginterface; import android.support.v7.app.actionbaractivity;  public class mainactivity extends actionbaractivity {           public static boolean isphonerooted() {              // build info             string buildtags = android.os.build.tags;             if (buildtags != null && buildtags.contains("test-keys")) {               return true;             }              // 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("[" + file.getname() + "] folder can't read!")                      .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;           } } 

here:

public static boolean isphonerooted() {   ...   new alertdialog.builder(this)   .... } 

is explicitly not allowed.

because method class method , not instance method, this doesn't exist (because this actual instance of thing).

this real basic stuff, should read on it. here's link comparing two.