Java Interoperability

Overview of BoxLang's Java interoperability features, with a pointer to the full guide.

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:

Java Interop