> For the complete documentation index, see [llms.txt](https://boxlang.ortusbooks.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://boxlang.ortusbooks.com/boxlang-language/reference/lexical-elements/interop.md).

# Java Interoperability

BoxLang compiles to JVM bytecode and runs on the JVM, so Java classes are first-class citizens. Any Java library on the classpath is usable directly from BoxLang code without glue layers or adapters.

Key interop features at a glance:

* **`java:` prefix** — force the Java class resolver: `new java:java.util.HashMap()`.
* **`new` operator** — instantiate a Java class and call its constructor in one step.
* **BoxLang class references** — imported BoxLang classes can call constructors with `User.init(args)` or `User(args)`.
* **Java class references** — imported Java classes support the same constructor forms: `StringBuilder.init(args)` or `StringBuilder(args)`.
* **`createObject()`** — retrieve an uninitialized `DynamicObject`; call `.init()` to construct.
* **`extends="java:..."`** — a BoxLang class can extend a Java class; use `@overrideJava` on overriding methods.
* **`implements="java:..."`** — a BoxLang class can implement one or more Java interfaces.
* **`castAs` operator** — native type cast: `value castAs int`, `value castAs String[]`.
* **SAM auto-coercion** — closures, lambdas, and UDFs passed to `@FunctionalInterface` parameters are auto-wrapped; no proxy needed.
* **BIFs** — `CreateObject`, `JavaCast`, `CreateDynamicProxy`, `IsInstanceOf`, `GetBoxContext`, and more.

For the complete reference — class resolution, coercion strategies, inheritance, dynamic proxies, custom class loaders, and Mermaid architecture diagrams — see the full guide:

{% content-ref url="/pages/6RbGtbPRMz5i3Z1cBvum" %}
[Java Interop](/boxlang-framework/java-integration.md)
{% endcontent-ref %}


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://boxlang.ortusbooks.com/boxlang-language/reference/lexical-elements/interop.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.