hi alpha, i did take the course. But i knew that it depends on the hours specified for the course and its about 40-48 hrs.. So u cld take them in 5, 10 or 20 days as u specify.
Thats all i can provide u
Wish u good luck

yes, you can cram the information into your head in a few weeks. BUT if you do that you won't actually know any of it, you'll have shortterm retention just long enough to pass the exam.
And without practical experience to back it up that knowledge is worthless anyway, possibly worth than useless as book knowledge without knowledge about its realworld application is extremely dangerous.

If you're serious about learning Java, rather than just cramming for the exam to get another acronym on your resume, take several months at least to seriously dive into the subject and learn not just the lines but what they actually mean and why they are as they are.

It's worth noting as well, that if the recruiter is ignoring your C++ experience and pushing you to get Java certified when you do not have any Java experience, then the recruiter is probably worthless. Making a recommendation to learn Java because there are a lot of employment opportunities is fine, but asking you to get certified and get back to him makes the impression that he just wants to shove you into a position quickly with no regard to your ability to perform it. He just wants to get paid.

As far as study time, that depends entirely on you and how quickly you can learn enough to pass it. You don't have to take a course to take the exam. There are a ton of preparation courses out there that would love to charge you a huge fee, but you can study up for the exam on your own just fine.

that's how recruiters think... If you survive the initial trial period at the place they put you they get paid a ton of money (usually a good portion of your yearly income).

Mind there are some recruiters who care, seeking a longterm business relationship with the companies they send you to, but the vast majority use it as a get-rich-quick scheme, hoping to retire in a few years.
If they can place 2 people per week at €10.000 each that's even after taxes a quarter million income a year.
If business expenses are half that again (unlikely) you're talking €125.000 net profit per year per recruiter working for the recruitment firm.

At that money most don't care if the potential well of customers dries up after a few years, they'll be made.

And of course in some parts of the world HR flunkies are still wood more by acronyms on a resume than by work experience, and will hire people as long as they have the correct ones listed without second thought, leaving it up to the workfloor to weed out the chaff from the corn (or more likely as these are often bodyshops, leaving it to the customers' workfloors).