You can do almost all hazelcast operations with Java Client. It already implements the same interface. You must include hazelcast-client.jar into your classpath.

import com.hazelcast.core.HazelcastInstance;
import com.hazelcast.client.HazelcastClient;

import java.util.Map;
import java.util.Collection;


ClientConfig clientConfig = new ClientConfig();
clientConfig.getGroupConfig().setName("dev").setPassword("dev-pass");
clientConfig.addAddress("10.90.0.1", "10.90.0.2:5702");

HazelcastInstance client = HazelcastClient.newHazelcastClient(clientConfig);
//All cluster operations that you can do with ordinary HazelcastInstance
Map<String, Customer> mapCustomers = client.getMap("customers");
mapCustomers.put("1", new Customer("Joe", "Smith"));
mapCustomers.put("2", new Customer("Ali", "Selam"));
mapCustomers.put("3", new Customer("Avi", "Noyan"));

Collection<Customer> colCustomers = mapCustomers.values();
for (Customer customer : colCustomers) {
     // process customer
}

You can use native C# client to connect to the running Hazelcast instances. All you need is to include Hazelcast.Client.dll into your C# project. The API is very similar to Java native client. Note that C# client doesn't have automatic reconnection feature. If the node that it connected dies, it will not switch to another member. User must connect to another member itself.

using System;
using System.Collections.Generic;

using Hazelcast.Client;
using Hazelcast.Core;

ClientConfig clientConfig = new ClientConfig();
clientConfig.GroupConfig.Name = "dev";
clientConfig.GroupConfig.Password = "dev-pass";
clientConfig.addAddress("10.90.0.1");

HazelcastClient client = HazelcastClient.newHazelcastClient(clientConfig);
//Allmost all cluster operations that you can do with ordinary HazelcastInstance
//Note that the Customer class must have Serializable attribute or implement Hazelcast.IO.DataSerializable
IMap<String, Customer> mapCustomers = client.getMap("customers");
mapCustomers.put("1", new Customer("Joe", "Smith"));
mapCustomers.put("2", new Customer("Ali", "Selam"));
mapCustomers.put("3", new Customer("Avi", "Noyan"));

ICollection<Customer> colCustomers = mapCustomers.values();
foreach (Customer customer in colCustomers) {
     // process customer
}

You can serialize back and forth Java and C# Objects between C# client and Hazelcast server. All you need is to have your classes that you want to share to implement DataSerializable both on Java and C# in the exact same way. And on C# ClientConfig you must set a TypeConverter implementation that will convert Java Class name into C# Type and vice versa. A basic TypeConverter might look like this.

public class MyTypeConverter: Hazelcast.IO.ITypeConverter
{
    public string getJavaName(Type type)
    {
        if(type.Equals(typeof(Hazelcast.Client.Examples.MyCSharpClass)))
            return "com.hazelcast.examples.MyClass";

        return null;
    }

    public Type getType(String javaName)
    {
        if("com.hazelcast.examples.MyClass".Equals(javaName))
            return typeof(Hazelcast.Client.Examples.MyCSharpClass);

        return null;
    }
}

            

A basic MyCSharpClass implementing DataSerializable

using System;
using Hazelcast.IO;

public class MyCSharpClass: Hazelcast.IO.DataSerializable
{
    String field1 = "";
    int field2;

    public MyCSharpClass ()
    {
    }

    public MyCSharpClass (String f1, int f2)
    {
        this.field1 = f1;
        this.field2 = f2;
    }

    public void writeData(IDataOutput dout){
        dout.writeUTF(field1);
        dout.writeInt(field2);
    }

    public void readData(IDataInput din){
        field1 = din.readUTF();
        field2 = din.readInt();
    }
}