Define a Timer after the class.
static volatile int time; Timer t = new Timer();
now edit your function like this
botonok.setOnClickListener(new OnClickListener()
{
public void onClick(View v)
{
Resources res = getResources();
myString = res.getStringArray(R.array.myArray);
String a = myString[rgenerator.nextInt(myString.length)];
time=1;
t.scheduleAtFixedRate(new TimerTask() {
@Override
public void run() {
runOnUiThread(new Runnable() {
public void run() {
TextView elemento1 = (TextView) findViewById(R.id.elemento1);
if(time==0||time==2||time==4||time==6)
elemento1.setText(a);
time=time+1;
}
}
});
}
}, 100, 1000);