Use the spannable string builder for setting as text in textview :
contentView.setText(sb);
or else you can do like this :
SpannableStringBuilder spanstr = new SpannableStringBuilder("Bold please!");
spanstr.setSpan(new StyleSpan(Typeface.BOLD), 0, spanstr.length(), Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
spanstr.append("\n");
spanstr.append("The first line is bold. This one isn't.");
contentView.setText(spanstr);