How to make a sidescroller camera

How to make a sidescroller camera

So me and a friend are wanting to make a sidescroller but we have come
into an issue with the camera. How can we make a camera that will follow
the player but not in a hard scrolling but instead a soft scrolling. What
I mean by that is that the camera will move only when the player moves to
a certain position on the window. We are using java to code this but I
think any language could help as long as it shares the same concept.