Try this code
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
spinner = (Spinner)findViewById(R.id.spinner1);
ageSpinner();
ArrayAdapter<Integer> spinnerAdapter = new ArrayAdapter<Integer>(this, android.R.layout.simple_spinner_item, list);
spinnerAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(spinnerAdapter);
}
private void ageSpinner(){
list = new ArrayList<Integer>();
for(int i=0; i<=4; i++){
list.add(i);
}