In the movie "Annie Hall," Woody Allen's character compares a relationship to a shark: "It has to constantly move forward or it dies."

The same rule seems to apply to towns. Behind every successful downtown business district, there is a group of people pushing it forward, making sure it doesn't die. That constant effort, over many years, can make the difference between a declining and a thriving downtown.

You can see this playing out in the revival of Hammonton's downtown. Casual observers will have noticed an influx of new businesses and activities in the past five years or so, but they may not realize these recent developments are the fruit of many years of labor.

Main Street Hammonton, part of the national Main Street program, is marking its 20th anniversary. The organization coordinates marketing, secures grant money and runs Third Thursdays, when entertainers and discounts draw shoppers to downtown stores.

Even before that group was formed, the town's Chamber of Commerce was planning events and creating the Hammonton Revitalization Corp., which offered loans to businesses, purchased new lighting fixtures and planted trees. As a result, the downtown vacancy rate has dropped from 60 percent - in the dark days when it looked as though suburban malls had all but killed small-town shopping districts - to 5 percent today.

Recent years have seen new downtown businesses - including sidewalk cafes, a wine bar and an art gallery run by the Noyes Museum - and the revival of the Eagle Theatre. Richard Stockton College has opened a satellite classroom building in town.

Hammonton still celebrates its agricultural heritage - and its claim to being the birthplace of the blueberry - with an annual Red, White and Blueberry Festival. The NJ Transit rail line and access to major highways such as the Atlantic City Expressway, Route 30 and Route 206 make the town a hub for commuters.

As people move to Hammonton - the population has grown 17 percent since 2000 - they bring their business ideas with them. While the town has one of the highest concentrations of Italian Americans in the U.S., it now also has a large Hispanic population - and a growing reputation as a center for Mexican food.

Downtown revivals don't happen overnight. They also never really stop. The reinvention and the hard work have to continue to keep the shark moving forward. Fortunately, Hammonton seems to have found the right combination of people and ideas to do just that.