HONG KONG — Nearly a year after the Japanese began to hope that their economy could turn around under new leadership, a sense of realism is replacing the euphoria.

Economists and investors have grasped just how difficult it will be for Prime Minister Shinzo Abe to sustain the growth of the last few months. Nowhere is that sentiment more evident than the Japanese stock market. The Nikkei 225 index is now nearly 40 percent above where it started the year, but the gains during the last four months have been slight — just 3.4 percent.

The economic recovery Mr. Abe engineered during the last year has been remarkable given the decades Japan in which languished. Buoyed by a big pickup in public works spending and a Bank of Japan policy of flooding the economy with low-interest money, growth has accelerated markedly. Deflation, the country’s biggest economic problem, seems to have disappeared.

The Japanese central bank said on Thursday that it now expected the economy to expand 1.5 percent in the year starting next April, up from a previous forecast of 1.3 percent.