Java doesn't have the concept of optional parameters with default values either in constructors or in methods. You're basically stuck with overloading. However, you chain constructors easily so you don't need to repeat the code:
public Foo(int param1, int param2)
{
this.param1 = param1;
this.param2 = param2;
}
public Foo(int param1)
{
this(param1, 2);
}