API / Apache FreeMarker Interview questions
What is the difference between the?? and! operators?
Both deal with missing values, but they answer different questions.
| Operator | Purpose | Returns | Example |
| ?? | Tests whether a value exists | A boolean | <#if user.middleName??> |
| ! | Supplies a default when a value is missing | The value itself, or the default | ${user.middleName!"N/A"} |
They are often combined: ?? is used inside an <#if> to decide whether to render a whole block, while ! is used inline to keep a single interpolation from failing. For a nested path where any segment could be absent, wrapping the path before applying either operator, such as (user.address.city)!"Unknown", protects the whole chain rather than just the last property.
What type of value does the ?? operator produce?
Which operator would you use to render an entire optional block only if a value is present?
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