How to get know the OwnerType of a case is Queue in Salesforce apex?

Hello,

you can check

if(string.valueOf(c.OwnerId).startsWith('005'))
{
//owner is User
}

if(string.valueOf(c.OwnerId).startsWith('00G'))
{
//owner is Queue
}

This can save you a SOQL and is standard across all ORGS in salesforce

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