Java share a variable between two threads

I have two threads. One invokes the update method of a class that modifies a variable. Another invokes the update method of a class that reads the variable. Only one thread writes and one (or more) threads read that variable. What do I need to do in terms of concurrency, since I am new to multi-threading?

public class A
{
    public int variable; // Does this need to be volatile?
       // Not only int, could also be boolean or float.
    public void update()
    {
        // Called by one thread constantly
        ++variable;
        // Or some other algorithm
        variable = complexAlgorithm();
    }
}

public class B
{
    public A a;
    public void update()
    {
        // Called by another thread constantly
        // I don't care about missing an update
        int v = a.variable;
        // Do algorithm with v...
    }
}

Thanks,