How to  initialize a list of strings in Apex?

I have a Map<String, Object> named idCollection.

Retrieval of a single string value is achieved through:

Object accountIdObject = idCollection.get('accountId');

I have confirmed that accountIdObject is indeed a string. My goal is to incorporate it into a List<String> named accountId.

In Java, this task is straightforward, allowing the direct assignment of a single string to a new list:

List<String> accountId = Arrays.asList((String) accountIdObject);

What’s the optimal approach for similar initialization in Apex?

I attempted the following, which resulted in the error: Illegal assignment from Object to List.

List<String> accountId = new List<String>{(String) accountIdObject};

However, I’ve verified that accountIdObject is a string, as indicated by accountIdObject instanceof String returning true.

Answer:

A detailed version of the desired code would be:

Object accountIdObject = idCollection.get('accountId');
String[] idValues;
if (accountIdObject instanceOf String) {
  idValues = new List<String>{ (String) accountIdObject };
}
if (accountIdObject instanceOf List<String>) {
  idValues = (List<String>) accountIdObject;
}

For a more concise form of code, consider:

List<String> accountId = accountIdObject instanceof String
   ? new List<String>{ (String) accountIdObject }
   : (List<String>) accountIdObject; 

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