player.setDataSource (URL); giving error

I have the code below that opens a URL for Streaming from a web radio and rings / pauses.

I have and errors in this código that I do not think at all and I ask for your help.

package carcleo.com.player;

import android.media.MediaPlayer;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import java.io.IOException;

public class player extends AppCompatActivity {

    private MediaPlayer player;
    private String URL;
    private Button btnPlayPause;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.player);

        URL               = "rtsp://cdn-the-2.musicradio.com:80/LiveAudio/Capital";
        btnPlayPause      = (Button)  findViewById(R.id.btnPlayPause);

        btnPlayPause.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                try {
                    btnPlayPause.setText("Carregando...");
                    if (player == null) player = new MediaPlayer();
                    tocaPausa();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        });

    }

    private void tocaPausa () throws IOException {

        if (!player.isPlaying()) {

            player.setDataSource(URL);

            player.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
                @Override
                public void onCompletion(MediaPlayer mediaPlayer) {
                    mediaPlayer.stop();
                    mediaPlayer.reset();
                }
            });

            player.prepare();
            player.start();
            btnPlayPause.setText("Pausar");

        } else {

            player.pause();
            btnPlayPause.setText("Tocar");

        }
    }
}

The 2 problems are:

A) On onCreate I have the setOnClickListener button that tries to change your text. It just does not work, the text does not change, but the line below runs normally.

    btnPlayPause.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            try {
                btnPlayPause.setText("Carregando...");
                if (player == null) player = new MediaPlayer();
                tocaPausa();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    });

I tried putting

btnPlayPause.setText("Carregando...");

within:

    player.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
        @Override
        public void onCompletion(MediaPlayer mediaPlayer) {

            btnPlayPause.setText("Carregando...");
            mediaPlayer.stop();
            mediaPlayer.reset();
        }
    });

But it turned out the same.

B) Well, here is more difficult. When I open the player, I click the button and after about 12 seconds the radio starts playing, when I click the button again, the radio is paused normally. But when I click again to play again, it gives error on line 43 of the tocaPausa() method.

player.setDataSource(URL);

Here is the error:

D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
    Process: carcleo.com.player, PID: 365
    java.lang.IllegalStateException
        at android.media.MediaPlayer.nativeSetDataSource(Native Method)
        at android.media.MediaPlayer.setDataSource(MediaPlayer.java:1078)
        at android.media.MediaPlayer.setDataSource(MediaPlayer.java:1039)
        at carcleo.com.player.player.tocaPausa(player.java:43)
        at carcleo.com.player.player.access$200(player.java:10)
        at carcleo.com.player.player$1.onClick(player.java:30)
        at android.view.View.performClick(View.java:5640)
        at android.view.View$PerformClick.run(View.java:22455)
        at android.os.Handler.handleCallback(Handler.java:751)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6165)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:888)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:778)