java - Error:(21, 8) error: class MyActivity is public - Can't edit MyActivity -

when trying edit myactivity, opens mainactivity.java.

when trying change read flag error message shows up

failed change read-only flag /root/androidstudioprojects/myapplication3/app/src/main/java/xyz/adamstephenson/android/myapplication/mainactivity.java

i'm trying make public class outputs information when button pressed on android.

the error is:

error:(21, 8) error: class myactivity public, should declared in file named myactivity.java

package xyz.adamstephenson.android.myapplication;  import android.app.activity; import android.os.bundle; import android.util.log; import android.view.view; import android.widget.button; import android.content.intent;  import static xyz.adamstephenson.android.myapplication.r.layout.activity_main;   public class myactivity extends activity {     protected void oncreate(bundle icicle) {         super.oncreate(icicle);          setcontentview(activity_main);          final button button = (button) findviewbyid(r.id.button);         button.setonclicklistener(new view.onclicklistener() {             public void onclick(view v) {                 log.d("button", "this message");             }         });     } } 

this error occurs when class file name not same class name inside class file.

in drive make class

a.java  write  public class a1{} 

it throw exception : class a1 public, should declared in file named a1.java

how ever if following

a.java , code  class a1{} 

above not throw exception, class not accessible outside package.