I accidentally opened this hierarchy/directory, or whatever tab in my eclipse oxygen... It is slowing down my eclipse because whenever I click something it updates and shows the information of that method/variable... How can I close it? It is enclosed by the red rectangle in the picture below. I tried to google it, but it is very hard to find useful results when I don't even know what this is called... Many thanks!
It's called breadcrumb.
There's a button in the global toolbar, called Toogle Breadcrumb
.
In my eclipse there's no keybinding for it, but you can configure this via Window
-> Preference
-> General
-> Keys
. The corresponding command is called Toggle Java Editor Breadcrumb
.