The Threads view shows the threads and their parent thread groups.
The current thread is indicated by an icon with a bold outline. Setting the current thread controls which frames are shown in the Call Stack view. This is done by double-clicking on the thread node, or by selecting Set Current from the context menu.
The view updates its contents when ever the session is suspended, whether by hitting a breakpoint, or if the Pause action is invoked. To cause the view to refresh while the debuggee is running, simply invoke the Refresh item in the view context menu.
By selecting a thread and invoking the Trace Methods item in the node context menu, a trace breakpoint will be created. It will be filtered by the name of the thread and indicate every time when any method is entered or exited while executing in the named thread. The output will be in the debugger console (in the Output window).
The view context menu has other actions available.
The Threads view, like other tree-structured views, will attempt to keep the expanded branches open while stepping through code. If, however, you have clicked on a column header in the view in order to sort the display, the tree will always collapse when it is updated. This is apparently a feature the tree-table component in the NetBeans Platform.