code: public void check(int id) {
          // don't even bother
          if (id != -1 && (id == mCheckedId)) {
              return;
          }
  
          if (mCheckedId != -1) {
              setCheckedStateForView(mCheckedId, false);
          }
  
          if (id != -1) {
              setCheckedStateForView(id, true);
          }
  
          setCheckedId(id);
      }
docs: <p>Sets the selection to the radio button whose identifier is passed in
  parameter. Using -1 as the selection identifier clears the selection; such an operation is
  equivalent to invoking {@link #clearCheck()}.</p>
  
  @param id the unique id of the radio button to select in this group
  @see #getCheckedRadioButtonId()
  @see #clearCheck()