我的旋转器出了点问题

所以我正在启动一个应用程序,首先要做的是在选择城市时对城市进行描述。我可以显示描述,但它同时对所有城市进行描述,并且当我选择另一个城市时不会显示出来:它会添加越来越多的内容。

这是我的代码:

公共类主扩展活动实现OnItemLickListener、OnItemSelectedListener{

TextView description;
Spinner spin;
ArrayAdapter adapter_city;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);


    description = (TextView)findViewById(R.id.description);

    spin = (Spinner)findViewById(R.id.spin);

    adapter_city = ArrayAdapter.createFromResource(this, R.array.Cities, android.R.layout.simple_spinner_item);
    adapter_city.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spin.setAdapter(adapter_city);
    spin.setOnItemSelectedListener(this);
}
@Override
public void onItemClick(AdapterView<?> parent, View v, int position, long id) {


}
@Override
public void onItemSelected(AdapterView<?> parent, View v, int position,
        long id) {
    switch(position){

    case 0 :    description.append(getString(R.string.Paris));

    case 1 :    description.append(getString(R.string.Chicago));

    case 2 :    description.append(getString(R.string.NewYork));
    }




}
@Override
public void onNothingSelected(AdapterView<?> parent) {

}

谢谢您。