Stocks in Japan jumped the most in more than seven years on Wednesday, shaking off unease about slowing growth in China amid a tentative rebound in Chinese stocks. The Nikkei Stock Average jumped 7.7%, or 1343.43, to 18770.51, marking the benchmark’s biggest daily percentage gain since October 2008. In point terms, it was the biggest gain since January 1994. A broad rally for shares and currencies comes after markets in the region fell Tuesday on weak Chinese trade data that had stoked concerns about a further slowdown in the world’s second-largest economy. Japanese stocks hit a seven-month low Tuesday. But on Wednesday, investor sentiment toward China took a positive turn.