massupdate.cls

public void massUpdate() {
    // first loop (don't forget to use Lists
    for (List < Contact > contacts: [SELECT FirstName, LastName FROM Contact]) {
        for (Contact c: contacts) { // 2nd for loop
            if (c.FirstName == 'Barbara' &&
                c.LastName == 'Gordon') {
                c.LastName = 'Wayne';
            }
        }
        update contacts; // update is part of the 1st for loop
    }
}