Read text file from URL and output to TextView

Probably because you are using StringBuilder which is not a CharSequence. Use output.setText(text.toString()); instead of output.setText((CharSequence) text);

TextView.setText() expects a CharSequence as an argument. String is a CharSequence, but StringBuilder is not. To get a String you gave to call StringBuilder.toString()

You should look at the crash though. And post it next time you ask a question on stackoverflow.

The crash log you provided clearly states the reason for crash: android.os.NetworkOnMainThreadException. It means that you are trying to do a network operation on the main thread and the Android OS does not let you. It is a rule since Honeycomb. The solution is to use AsyncTask, for example. Here is an article about network ops and AsyncTask.

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.StringBuilderPrinter;
import android.widget.TextView;
import android.widget.Toast;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

public class MainActivity extends AppCompatActivity {

    private TextView textView;
    private StringBuilder text = new StringBuilder();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        BufferedReader reader = null;

       new AsyncTask<Void,Void,Void>(){


            @Override
            protected Void doInBackground(Void... params) {
 try {

            URL url = new URL("http://something.uk/pmt/status.txt");


            reader = new BufferedReader(
                    new InputStreamReader(url.openStream()));


            String str;


            while ((str = reader.readLine()) != null) {
                text.append(str);
                text.append('\n');
            }

        } catch (IOException e) {
            Toast.makeText(getApplicationContext(), "Error reading file.", Toast.LENGTH_LONG).show();
            e.printStackTrace();
        } finally {
            if (reader != null) {
                try {
                    reader.close();
                } catch (MalformedURLException e) {

                }

                catch (IOException e) {

                }
            }
                return null;
            }

   @Override
            protected void onPostExecute(Void aVoid) {
                super.onPostExecute(aVoid);
            TextView output = (TextView) findViewById(R.id.textView);
            output.setText(text.toString());
            }
        }.execute(null,null,null);


        }
    }
}