> For the complete documentation index, see [llms.txt](https://eric-lo.gitbook.io/lab-grpc/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://eric-lo.gitbook.io/lab-grpc/implement-the-client-in-java.md).

# Implement the client in Java

We now write a simple Java client program to call the **CalculatorService.**

Create `CalculatorClient.java` in `src/main/cslab/grpclab`:

```bash
cd ~/grpclab
nano src/main/java/cslab/grpclab/CalculatorClient.java
```

{% code title="CalculatorClient.java" %}

```java
package cslab.grpclab;

import io.grpc.Channel;
import io.grpc.ManagedChannelBuilder;

public class CalculatorClient {
    public static void main(String[] args){
        //Create a connection to `CalculatorServer`
        Channel channel = ManagedChannelBuilder.forAddress("127.0.0.1", 8980)
                                                .usePlaintext() // disable TLS
                                                .build();

        //Create a stub of Calculator service for invoking the method of Calculator service later on
        CalculatorGrpc.CalculatorBlockingStub stub = CalculatorGrpc.newBlockingStub(channel);

        // Calculate "1 + 1" by calling the CalculatorService
        float a = 1;
        float b = 1;

        //Create the `CalculationRequest` object and set the value of `a` and `b`
        CalculatorOuterClass.CalculationRequest request = CalculatorOuterClass.CalculationRequest.newBuilder()
                                                            .setA(a)
                                                            .setB(b)
                                                            .build();

        //Invoking the `sum` function of `CalculatorService` through the stub
        CalculatorOuterClass.CalculationRespond respond = stub.sum(request);
        System.out.println(String.format("JavaClient: The result of %f + %f = %f", a, b, respond.getResult()));

        // Calculate "3 x 2" by calling the CalculatorService
        a = 3;
        b = 2;
        request = CalculatorOuterClass.CalculationRequest.newBuilder()
                                                            .setA(a)
                                                            .setB(b)
                                                            .build();
        respond = stub.product(request);
        System.out.println(String.format("JavaClient: The result of %f x %f = %f", a, b, respond.getResult()));

    }
}
```

{% endcode %}

## Compile your program

Again we need to compile our code into the JAR. Execute the following command.

```bash
mvn package
```

`grpclab-1-jar-with-dependencies.jar` will be generated under `target` which contains the bytecode of your program and dependency libraries.  

## Test your program

Now we have the `CalculatorServer` and `CalculatorClient`. We can test our programs.

Launch the `CalculatorServer` in the background:

```
java -cp target/grpclab-1-jar-with-dependencies.jar cslab.grpclab.CalculatorServer &
```

Launch the `CalculatorClient`:

```bash
java -cp target/grpclab-1-jar-with-dependencies.jar cslab.grpclab.CalculatorClient 
```

You should see the following output from `CalculatorClient`:

```
JavaClient: The result of 1.000000 + 1.000000 = 2.000000
JavaClient: The result of 3.000000 x 2.000000 = 6.000000
```

You can kill the `CalculatorServer` by using command:

```bash
kill %1
```