Probation in criminal law is a period of supervision over an offender, ordered by a court instead of serving time in prison. In some jurisdictions, the term probation only applies to community sentences (alternatives to incarceration), such as suspended sentences.
When your landlord changes your door locks because you are behind on paying the rent, the landlord must give you advanced written notice of the proposed lock change AND a written notice at the time your locks are changed.
A landlord can only enter your apartment for one of the reasons covered under CA Civil Code 1954, which includes to do repairs, for an emergency and under court order. A landlord can not lock you out of your apartment, even if he has a just cause.