How to call second class method from one class and print output of method inside second class in java

Question

MqConnection.java

package com.example.rabbitmq;

import android.os.StrictMode;
import android.util.Log;

import com.rabbitmq.client.ConnectionFactory;

import java.io.IOException;
import java.util.concurrent.TimeoutException;

final static String QUEUE_NAME = "hello2";
final static String EXCHANGE_NAME = "logs_monitor";

final static String HOST = "localhost";
final static int PORT = 5672;
final static Connection connection;
final static Channel channel;

public class MqConnection {
    public void setupConnection() {
        Log.d("Debug","SetupConnection connected");
        ConnectionFactory factory = new ConnectionFactory();
        try {
            factory.setHost(HOST);
            factory.setPort(PORT);
//            factory.setVirtualHost("/");
//            factory.setUsername(USERNAME);
//            factory.setPassword(PASSWORD);

            StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
            StrictMode.setThreadPolicy(policy);

            connection = factory.newConnection();
            channel = connection.createChannel();

        } catch (IOException | TimeoutException e) {
            throw new RuntimeException("Rabbitmq problem", e);
        }
    }
}

MqConsume.java

package com.example.rabbitmq;

import android.util.Log;
import com.rabbitmq.client.BuiltinExchangeType;
import com.rabbitmq.client.DeliverCallback;

import java.io.IOException;

import static com.example.rabbitmq.setVariables.EXCHANGE_NAME;
//import static com.example.rabbitmq.setVariables.QUEUE_NAME;
import static com.example.rabbitmq.setVariables.QUEUE_NAME;
import static com.example.rabbitmq.setVariables.channel;
import com.example.rabbitmq.MainActivity.*;

public class MqConsume {
    static String message = "";
    public static void consumeMessages(String[] args) throws IOException {
        Log.d("Debug","Before rabbitmq publish");
//        channel.exchangeDeclare(EXCHANGE_NAME,"fanout");
        channel.queueDeclare(QUEUE_NAME,true,false,false,null);
        channel.queueBind(QUEUE_NAME, EXCHANGE_NAME, "");
        DeliverCallback deliverCallback = (consumerTag, delivery) -> {
            message = new String(delivery.getBody(), "UTF-8");
            Log.d("Debug","Received");
            Log.d("Debug",message);
        };
        channel.basicConsume(QUEUE_NAME, true, deliverCallback, consumerTag -> { });
    }
}

MainActivity.java

package com.example.rabbitmq;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.TextView;

import java.io.IOException;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        MqConnection mqConnection = new MqConnection();
        mqConnection.setupConnection();

        MqConsume mqConsume = new MqConsume();
        final TextView received_msg;
        received_msg = findViewById(R.id.received_messages);
        System.out.println(received_msg);
    }
}

Here i am Using Android Studio code with backend java code to connect rabbitmq. How to call message parameter in MqConsume.java from MainActivity.java

I need to print message parameter inside MainActivity class from MqConsume.java .

I have tried Calling MqConsume.java inside MainActivity.java and print message parameter inside MainActivity.java .

Is there any way to get data from one class to other class?

Answer 1

It looks like you want to retrieve data from an asynchronous API and use it in your activity. You can do this by declaring a custom interface and passing an instance of it to the function making the API call. Have a look here for more details about why this is needed.

public class MqConsume {

    // declare a callback interface
    public interface GotMessage {
        void gotMessage(String msg);
    }
    
    // pass the interface in here and call it when 
    // the message is received
    public static void consumeMessages(String[] args, GotMessage callback) throws IOException {
        Log.d("Debug","Before rabbitmq publish");

        channel.queueDeclare(QUEUE_NAME,true,false,false,null);
        channel.queueBind(QUEUE_NAME, EXCHANGE_NAME, "");
        
        DeliverCallback deliverCallback = (consumerTag, delivery) -> {
            String message = new String(delivery.getBody(), "UTF-8");
            Log.d("Debug","Received");
            Log.d("Debug",message);
            callback.gotMessage(message);
        };
        
        channel.basicConsume(QUEUE_NAME, true, deliverCallback, consumerTag -> { });
    }
}

Then if you call it from MainActivity you can pass in a callback like this:

final TextView received_msg = findViewById(R.id.received_messages);

// create the interface in the activity and set
// view text inside it
MqConsume.consumeMessages(args, new MqConsume.GotMessage() {
    @Override
    void gotMessage(String message) {
        received_msg.setText(message);
    }
});