I'm using NetBeans with Java.
I have create a JFrame with some checkboxes and a button to open browser go to the specific URL based on the checkboxes' values.
But how do I auto-login/auto fill the username and password textbox then trigger the login button?
Please kindly advise.

hmm not this tho.
For example right, if the user only check 1 item which is will redirect to a particular website.
But I don't want enter the username and password again. Instead, when the JAVA prompted the browser to the user, it will be auto login already.

I have to disagree. That button in almost all sites triggers the form submit. As to the your new reply, this is just another get the form, change as you wish and do another form submit.

How long have you been working with such systems? This may be where you want to find tutorials on how web pages, forms and data works because without understanding how it works, you may be lost.

Also, why not Python? Watch https://www.youtube.com/watch?v=UtNYzv8gLbs as it gives you an idea of using an app to fill in and submit those forms.

Oh I am just randomly come out a simple business idea that I can sell this software only.
Because in my social network right, I saw a lot of people have to keep open different browsers then keep repeating the same login credential on different portal. Then I think, what if I can develop a software/application that can help them to push the browsers out with logged.
I have no knowledge on Python also, I had learn .NET and JAVA so far.

@gahhon. I was unclear. Where I think you are at is missing "how things work." This is not a code issue yet. You may have learned Java and .NET but you need to now learn how web pages work. The Python method or video gives us insight there but for you to build a BOT in Java, you need both Java and web knowledge.

Understood. Or maybe in what keyword/tutorial/advance I should look after for like how to add the data into the textbox when browser is open?
And also I do have their ID of those property

I would not suggest doing such work "when browser is open". Watch the video, albeit Python and notice that there was not a browser open when the submit stage was done. A browser is for the human to use. If you want to write a BOT that interacts with a web page, then a BOT doesn't need to open a browser.

If you insist on interacting with a browser, you will encounter a lot of pain and roadblocks. For that I would look at AutoIT scripts.

-> In parting the above sounds like a bot. There are many that do such bots then try to sell them. If you hide what you are trying to do, it gets very hard for others to either show you the way or comment on why that's a good or bad thing.