新生报到，求大牛指点。代码没提示错，但运行时就崩了，可能跟空指针有关，没头绪啊

package com.example.ilovedyou_;

import android.media.AudioManager;
import android.media.SoundPool;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends Activity {

    public Button[][] Btn;
    private SoundPool sp;
    private int music1,music2;
   
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        init();
    }
    private void init(){
        for(int i=0;i<6;i++)
            for(int j=0;j<9;j++)
        {
         Btn[i][j]=(Button)findViewById(R.id.Btn_00+9*i+j);
        }
        sp=new SoundPool(5,AudioManager.STREAM_SYSTEM,5);
        music1=sp.load(this,R.raw.cat,1);
        music2=sp.load(this,R.raw.dog,2);
      
        for(int i=0;i<6;i++)
            for(int j=0;j<9;j++)
        {
         Btn[i][j].setOnClickListener(listener);
        }
        
}
    private OnClickListener listener=new OnClickListener(){
        public void onClick(View v){
          if(v==Btn[0][1]||v==Btn[0][2]||v==Btn[0][5]||v==Btn[0][8]
            ||v==Btn[1][0]||v==Btn[1][4]||v==Btn[1][6]||v==Btn[1][8]
             ||v==Btn[2][0]||v==Btn[2][4]||v==Btn[2][6]||v==Btn[2][8]
              ||v==Btn[3][0]||v==Btn[3][4]||v==Btn[3][5]||v==Btn[3][6]||v==Btn[3][8]
               ||v==Btn[4][0]||v==Btn[4][4]||v==Btn[4][6]||v==Btn[4][8]
                ||v==Btn[5][1]||v==Btn[5][2]||v==Btn[5][4]||v==Btn[5][6]||v==Btn[5][8])
        {   
        sp.play(music1,1,1,0,0,1);
      
        }
        else
        {
        sp.play(music2,1,1,1,1,1);
        }
    }};
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }
}
logcat显示是01-25 07:25:33.490: E/AndroidRuntime(1384): Caused by: java.lang.NullPointerException
再次求大牛指点