I wanted to know is it legal for a landlord to change the locks and lockout a tenant without going to court?

No, the tenant will be able to sue the landlord and win a very large amount of money for a illegal eviction.

Absolutely not. That is considered a "self-help" eviction and it is illegal. If the tenant sues then the tenant will win big.

(You're talking about a residential tenancy, right? If you're referring to a commercial tenancy then that's a completely different story.)

Not even close! That's why evicition is a court process. Tenants have rights.