Android改变部分文字的字体大小

public class TestActivity extends Activity{

    private TextView mTvDate;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_test);

        mTvDate = (TextView)findViewById(R.id.tv_date);
        Spannable span = new SpannableString("2014-09-07");
        span.setSpan(new RelativeSizeSpan(1.5f), 0, 4, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
        span.setSpan(new ForegroundColorSpan(Color.RED), 0, 10, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
        span.setSpan(new BackgroundColorSpan(Color.YELLOW), 0, 10, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
        mTvDate.setText(span);
    }
}