Musikplayer stoppt nicht..

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <GridLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >
    </GridLayout>

    <Button
        android:id="@+id/btn_prev"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/btn_prev" />

    <Button
        android:id="@+id/btn_next"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/btn_next" />

    <Button
        android:id="@+id/btn_pause"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/btn_pause" />

    <Button
        android:id="@+id/btn_play"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/btn_play" />

    <SeekBar
        android:id="@+id/seekBar_volumen"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />




    <TextView
        android:id="@+id/textView_song_title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/textView_song_title" />

</LinearLayout>

package net.ibasic;

import java.io.IOException;

import android.app.Activity;
import android.media.MediaPlayer;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.SeekBar;
import android.widget.TextView;

public class MusicActivity extends Activity {
    /** Called when the activity is first created. */
    
	private TextView txt_song_title;
	
	private MediaPlayer mediaPlayer;
	//private int counter;
	
	@Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        /**/
        
        Button btn_prev = (Button) findViewById(R.id.btn_prev);
        Button btn_next = (Button) findViewById(R.id.btn_next);
        Button btn_pause = (Button) findViewById(R.id.btn_pause);
        Button btn_play = (Button) findViewById(R.id.btn_play);
        SeekBar seek_volumen = (SeekBar) findViewById(R.id.seekBar_volumen);
        txt_song_title = (TextView) findViewById(R.id.textView_song_title);
        
       // counter=0;
        /**/
        
        mediaPlayer = new MediaPlayer();
        
        /**/
        
        btn_next.setOnClickListener(new View.OnClickListener(){
        	
        	public void onClick(View view){
        		
        		//counter =counter +1 ;
        		
        		txt_song_title.setText(null); // Titel
        		        		
        		try{
        			mediaPlayer.reset();
        		}
        	        	
        	catch(Exception e){
        		//
        	}
        	
            MediaPlayer mediaPlayer = MediaPlayer.create(getApplicationContext(), R.raw.song);
            try {
				mediaPlayer.prepare();
			} catch (IllegalStateException e) {
				
				e.printStackTrace();
			} catch (IOException e) {
				
				e.printStackTrace();
			}
            mediaPlayer.start(); 
    
        	
        	}});
        
        btn_next.setOnClickListener(new View.OnClickListener(){
        	
        	public void onClick(View view){
        		        		
        	}
        	        	
        });
        
        btn_prev.setOnClickListener(new View.OnClickListener(){
        	
        	public void onClick(View view){
        		
        		try{
        			mediaPlayer.reset();
        		}
        	        	
        	catch(Exception e){
        		//
        	}
        	
        	txt_song_title.setText(null); // Titel
        	
        	
        	 try {
 				mediaPlayer.prepare();
 			} catch (IllegalStateException e) {
 				
 				e.printStackTrace();
 			} catch (IOException e) {
 				
 				e.printStackTrace();
 			}
             mediaPlayer.start(); 
     
        		        	}
        	        	
        });
        
        btn_play.setOnClickListener(new View.OnClickListener(){
        	
        	public void onClick(View view){

        		txt_song_title.setText(null); // Titel
        		
                MediaPlayer mediaPlayer = MediaPlayer.create(getApplicationContext(), R.raw.song);
                try {
					mediaPlayer.prepare();
				} catch (IllegalStateException e) {
					
					e.printStackTrace();
				} catch (IOException e) {
					
					e.printStackTrace();
				}
                mediaPlayer.start(); 
        
        		}
        	});
        
       btn_pause.setOnClickListener(new View.OnClickListener(){
        	
       public void onClick(View view){
    	   
    	   mediaPlayer.pause();
    	   mediaPlayer.stop();
       } 	
        
	});
        
        
        
        
    }

}