stop application with TIMER AND TIMERTASK - timer

Question

I am doing my app on android, when I run my application I can see the screen but when I give click show the message "THE APLICATION STOP", when i give click automatically run each time a random where the number that shown a color. I am using Timer and TimerTask.
public class HolaMundo extends AppCompatActivity {
ImageView fondoImg;
Button entrada;
int valorfinal;
TimerTask tareatiempo;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_hola_mundo);
fondoImg=(ImageView)findViewById(R.id.fondoPantalla);
entrada=(Button)findViewById(R.id.btnEncen);
final Timer tarea=new Timer();
entrada.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
tareatiempo = new TimerTask() {
#Override
public void run() {
busqueda();
}
};
tarea.scheduleAtFixedRate(tareatiempo,0,5000);
}
});
}
public void busqueda()
{
valorfinal=(int)(Math.random()*4+1);
switch (valorfinal)
{
case 1:
fondoImg.setImageResource(R.drawable.amarillo);
break;
case 2:
fondoImg.setImageResource(R.drawable.negro);
break;
case 3:
fondoImg.setImageResource(R.drawable.rojo);
break;
case 4:
fondoImg.setImageResource(R.drawable.verde);
break;
}
}