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public class MainListActivity extends ListActivity{
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event)  {
        if (android.os.Build.VERSION.SDK_INT < android.os.Build.VERSION_CODES.ECLAIR
                && keyCode == KeyEvent.KEYCODE_BACK
                && event.getRepeatCount() == 0) {
            // Take care of calling this method on earlier versions of
            // the platform where it doesn't exist.
            onBackPressed();
        }

        return super.onKeyDown(keyCode, event);
    }

    @Override
    public void onBackPressed() {
        // This will be called either automatically for you on 2.0
        // or later, or by the code above on earlier versions of the
        // platform.
                finish();
        return;
    }
}