Japan’s Nikkei index gained over 1,000 points in afternoon trading Tuesday, extending gains initially led by buying of technology shares on optimism about the outlook for the semiconductor market. The 225-issue Nikkei Stock Average has risen as high as 37,930.10 so far in the afternoon session, up 1,032.68 points, or 2.8 percent, from Friday. Financial markets in Japan were closed Monday for a public holiday.