I’ve seen several incoming searches like “SPWebApplication for Central Admin”, so hopefully this will provide a quick answer:
SPAdministrationWebApplication.Local
Which really just returns:
SPAdministrationWebApplication.GetInstanceLocalToFarm(SPFarm.Local);
And a quick example in PowerShell for good measure:
PS C:\> [system.reflection.assembly]::LoadWithPartialName("Microsoft.SharePoint") > $null
PS C:\> $ca = [Microsoft.SharePoint.Administration.SPAdministrationWebApplication]::Local
PS C:\> $ca.DefaultServerComment
SharePoint Central Administration v3
PS C:\> $ca.AdministrativeTasks.Items | select Title -first 3
Title
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Add anti-virus protection
READ FIRST - Click this link for deployment instructions
Configure Workflow Settings
Hope this helps!
Solutionizing .NET 