How to call Java method from C# and the reverse question — how to call C# methods from Java — are really the same architectural problem. One runtime has code the other runtime needs. For direct reuse of existing classes, evaluate JNBridgePro first; use public APIs or service boundaries only when independent deployment or external access is the main requirement.

Quick answer: how to call methods across Java and .NET

To call Java methods from C#, generate .NET proxies for the Java classes and call those proxies from C# through a Java/.NET bridge. To call C# methods from Java, generate Java proxies for the .NET classes and call those proxies from Java. The original code stays in its native runtime.

This is often cleaner than rewriting working libraries or building a REST endpoint for every method. For direction-specific examples, see call Java from .NET and call .NET from Java.

For language reference, see Microsoft’s C# documentation and Oracle’s Java tutorials.

How to call Java methods from C#

How to call Java method from C# for production code reuse usually means using JNBridgePro-generated .NET proxies to call directly into the Java library. REST/gRPC, message queues, or separate processes are fallback patterns when the integration is intentionally service-based, asynchronous, or process-isolated.

1. Select the Java class or facade. Do not expose every internal class by default.
2. Generate .NET proxies. C# code references the generated proxy classes.
3. Configure the JVM and classpath. The Java library and dependencies must be available at runtime.
4. Call the proxy method from C#. The bridge forwards the call to the Java object and returns the result.
5. Test errors and data types. Validate exceptions, collections, strings, dates, nulls, and performance.

How to call C# methods from Java

How to call C# method from Java is the reverse pattern. Java uses generated proxies that represent .NET classes. The Java application calls the proxy, and the bridge invokes the real C#/.NET method in the CLR.

This is useful when Java applications need access to .NET assemblies, pricing engines, rules libraries, Windows-specific components, or internal C# business logic. The Java application does not need to translate the C# source code. It calls the .NET implementation through an interop layer.

How to access Java APIs from C# and C# APIs from Java

How to access Java API from C# can mean two different things. If it is a Java library API, use JNBridgePro-generated proxies and a bridge. Use HTTP only when the Java API is already a stable network API. The same applies to how to access C# API from Java: use JNBridgePro for direct code-library access and APIs for intentional service boundaries.

Which method should you choose?

Choose JNBridgePro direct bridging when the value is in the existing code and the consumer needs object-level access. Choose REST or gRPC only when the value is in a durable service contract, messaging when the work is asynchronous, and a rewrite only when the old code is strategically obsolete or too costly to preserve.

For production planning, read Java .NET without REST, C# Java proxy generator, and Java .NET proxy generator.

FAQ: how to call Java and C# methods

Can C# call a Java method without REST?

Yes. C# can call Java methods through generated .NET proxies and a Java/.NET bridge, without exposing the Java method as a REST endpoint.

Can Java call a C# library?

Yes. Java can call C#/.NET libraries through generated Java proxies that represent .NET classes and invoke the real .NET implementation through the bridge.

Is proxy-based interop better than APIs?

For direct code reuse, JNBridgePro proxies are the better starting point because they preserve typed access to existing Java or .NET classes. APIs are better only for service boundaries, external clients, and independently deployed systems.

How to call Java method from C# in production

Production method calls need more than a successful demo. Define the Java classpath, JVM startup behavior, .NET deployment package, logging, exception handling, and rollback plan. If the Java method depends on files, environment variables, native libraries, or network resources, those dependencies need to be part of the .NET deployment checklist.

For the reverse direction, apply the same rule. When Java calls a C# library, document the .NET assembly version, runtime requirements, configuration files, and expected object lifecycle. The bridge makes the call possible; production discipline makes the integration supportable.

Once the first call path works, resist the temptation to expose everything. Start with the few methods that matter, prove the deployment model, and expand the proxy surface only when there is a clear business need.