TOKYO, March 11 (Reuters) - Japan's Nikkei average gained on Tuesday as investors scooped up battered commodity stocks, but trading volume was thin as caution over an economic slowdown in China and Ukraine tensions kept traders on the sidelines. As widely expected, the Bank of Japan maintained its massive monetary stimulus on the view that economic growth and consumer price increases remain on track, but it cut its view of exports in a warning that external demand will continue to disappoint. The Nikkei average ended 0.7 percent higher at 15,224.11, recouping more than a half of its losses from the previous day to edge back towards a five-week high of 15,312.60 hit on Friday. The broader Topix index rose 0.5 percent to 1,233.21, but only 1.81 billion shares changed hands, the lowest since mid-October. The JPX-Nikkei Index 400, a gauge comprising firms with high return on equity and strong corporate governance, advanced 0.5 percent to 11,157.14.