java-modelslisted

# Working with models in an APIMatic Java SDK Most request/response data are plain generated classes with a nested `Builder` (covered in `java-calling-endpoints`). This skill covers the **non-obvious model shapes** that trip integrations up. The patterns are generic across APIMatic Java SDKs; take the real type names from your SDK source under `<root>/models/`. ## The Builder split: required vs optional Every model class carries a nested `public static class Builder`. The split is mechanical: - **Required fields are constructor arguments** on the `Builder`. - **Optional fields are fluent setters** — and so are the required ones, so you can also override a constructor value later. - `build()` returns the model; `model.toBuilder()` returns a `Builder` pre-populated from an existing instance, which is how you derive a variant without re-listing every field. ```java {Model} m = new {Model}.Builder(requiredA, requiredB) .optionalC(value) .build(); {Model} variant = m.toBuilder().optionalC(other).build(); ``` A model with **no** required fields has no `Builder` constructor arguments at all — start from `new {Model}.Builder()`. A model that extends another names its clone method after itself (`to{Model}Builder()`) instead of `toBuilder()`. **This SDK's models are mutable**, so each field also has a plain `@JsonSetter` setter and the model has a no-arg constructor alongside the public all-args one. A model with required fields additionally gets a **no-arg