The singleton pattern

The singleton design pattern restricts the instantiation of a class to only one object.

This is a useful design pattern in Apex and is frequently used. As discussed in the previous chapter, Salesforce has various governor limits; for example, a number of SOQL queries, a number of query rows returned, and a number of DML operations that can be performed in a single request.

Using the singleton design pattern, we can make sure that utility classes are instantiated only once, which can help in avoiding governor limits.

The sales division of a call center receives calls either from a customer or broker who is interested in the product. If a call comes directly from a customer, then the call center agents need to create a new opportunity record with all the required information. Alternatively, if a call comes from a broker, then the call center agents need to create an opportunity record and then record it for a broker as well. Brokers are eligible for commission...