For the first time in decades, the New Jersey presidential primary could matter.

By the time the Garden State votes, the intended nominees of both parties are usually preparing for their conventions. But what happens "usually" isn't happening this year, is it?

Instead, both nominations may still be contested for another several weeks, raising the possibility that Jersey votes could count for something.

However, the wall-to-wall coverage of primaries in other states has created confusion about the Jersey primary - where the rules are very different, said Jesse Burns, interim executive director of the League of Women Voters New Jersey.

"We always see an increase in calls concerning primaries, because the primary system is more complicated than the general election," she said.

In New Jersey, both the Republicans and the Democrats hold their primaries on the same day. This year it's June 7.

If you are not registered, you need to register by May 17 in order to cast a primary ballot. (Use these links if you can't remember if you are registered or if you're looking for your polling location.)

New Jersey does not have online voter registration, Burns said.

"You have to print the form out, physically sign it, and mail it in," she said. Forms are available through the state Division of Elections website, at county board of elections, at municipal town halls, and at social services agencies such as motor vehicle offices.

People can also call the League office to request that one be mailed to them. That number is 800-792-VOTE (8683).

On the registration deadline day, May 17, most county board of election offices will be open until 9 p.m.

In order to register in New Jersey you must be:

A citizen of the United States

At least 18 years old

A resident of your county for at least 30 days before the election

And not currently serving a sentence, probation or parole because of a felony conviction.

What if you are already registered? Can you choose the party primary in which to vote?

"We're a closed primary. In New Jersey, you can only vote for your party's candidate," said Burns. (Only the Republican and Democratic parties choose their nominee through a primary; the other parties - such as the Green party - have a different nominating process.)

If you are an Undeclared voter (or what some erroneously call "Independent"), you may declare your affiliation up to and including primary election day - right at the polling place - and cast your ballot in that party's race. If you are voting in your very first primary, you can declare your party affiliation at the polls.

If you've already registered your party affiliation, you can vote only in that party's primary. You can't be on the Democratic rolls and cast a ballot in the Republican primary, or vice versa.

In order to do that, you'd have to change your party affiliation, and the deadline to do that is much sooner: April 13.

The form you'd need to fill out is called a Political Party Affiliation Declaration form, and it's available on the League of Women Voters website, as well as at the same places where the registration forms are available.

That a source of much confusion every primary, Burns said.

"On primary election day, we get a lot of calls saying 'I'm registered as such and such, and they tell me I can only vote in that primary,'" she said. "People think they can vote for whomever they want. In a closed primary system, that's just not the case."

But what's to stop someone registered in one party for secretly voting in the other primary once they enter the voting booth? Short answer: Technology. In computerized voting systems, "only one party's ballot will light up for you," said Burns.

Needless to say, your party affiliation isn't binding in the general election in November. Once you enter the polling booth, you can vote for whomever you want.

"People do confuse that as well," Burns said. "You can vote all around the ballot. You can vote Green, Republican, Democrat, whatever."

Just keep in mind that if you change your party affiliation for this year's primary, you'll remain in that party unless and until you switch it back.

If you temporarily affiliated just for this race, you might want to switch back to your usual party, or become unaffiliated, after you've cast your primary vote.

There is no limit to how many times a voter hops back and for the between parties, Burns indicated: "You can change your political party as often as you like."

Kathleen O'Brien may be reached at kobrien@njadvancemedia.com. Follow her on Twitter @OBrienLedger. Find NJ.com on Facebook.