Creating a simple weather forecasting app using Java is a great way to learn about programming and weather data. In this tutorial, we will walk through the steps to create a basic weather forecasting app that displays the current temperature and conditions for a given location.

1. First, you will need to obtain an API key from a weather data provider such as OpenWeatherMap. This key will allow you to access the weather data for a specific location.
2. Next, you will need to create a new Java project and add the necessary dependencies. These will include a library for making HTTP requests (such as OkHttp or Apache HttpClient) and a library for parsing JSON data (such as Gson or Jackson).
3. In your main class, create a method that uses the API key to make an HTTP request to the weather data provider’s API. This request should include the location for which you want to retrieve weather data. The API will return the data in JSON format, which you will then parse and extract the necessary information.
4. Once you have the weather data, you can display it in a user-friendly format. This can be done by creating a simple GUI using JavaFX or by printing the data to the console.
5. Finally, you can add additional features to your app, such as the ability to switch between Celsius and Fahrenheit, or to display a 5-day forecast.

Here is an example of a simple weather forecasting app that prints the current temperature and conditions for a given location to the console:

import okhttp3.*;
import com.google.gson.*;

public class WeatherApp {
    public static void main(String[] args) {
        // API key
        String API_KEY = "YOUR_API_KEY";
        // Location
        String location = "New York,US";
        // Weather data URL
        String url = "https://api.openweathermap.org/data/2.5/weather?q=" + location + "&appid=" + API_KEY;

        OkHttpClient client = new OkHttpClient();
        Request request = new Request.Builder().url(url).build();

        try {
            Response response = client.newCall(request).execute();
            String jsonData = response.body().string();
            Gson gson = new Gson();
            WeatherData data = gson.fromJson(jsonData, WeatherData.class);

            System.out.println("Temperature: " + data.main.temp + "°F");
            System.out.println("Conditions: " + data.weather[0].description);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

class WeatherData {
    Main main;
    Weather[] weather;
}

class Main {
    double temp;
}

class Weather {
    String description;
}

Please note that this example uses OkHttp and Gson libraries, you can use any other libraries for making HTTP requests and parsing JSON data of your choice.

With this basic knowledge, you should be able to create your own weather forecasting app using Java. You can also expand upon this tutorial by adding more features or by using different weather data providers. Happy coding!