Code Structure Reference - Currency Converter

Overview

This page provides a comprehensive reference for all classes, methods, and code structures in the Currency Converter application.

ConversorApp (Main Controller)

Package: lad.com.alura.conversormoneda.controladores Purpose: Application entry point and main controller that orchestrates the conversion flow.

Class Structure

package lad.com.alura.conversormoneda.controladores;

import lad.com.alura.conversormoneda.modelos.ConsultaMoneda;
import lad.com.alura.conversormoneda.vista.Conversor;
import lad.com.alura.conversormoneda.modelos.RegistroConversion;

import java.time.LocalDateTime;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class ConversorApp {
    public static void main(String[] args) {
        // Implementation
    }
}

main() Method

args

String[]

Command-line arguments (not used in current implementation)

returns

void

No return value

Complete Implementation

Main Method
Currency Selection Logic

public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    // Instantiate service (OOP)
    ConsultaMoneda consulta = new ConsultaMoneda();
    // Create history list
    List<RegistroConversion> historial = new ArrayList<>();

    int opcion;

    while (true) {
        // Display menu
        Conversor.eleccionUserMenu();
        opcion = sc.nextInt();

        if (opcion == 8) {
            System.out.println("Gracias por usar el conversor.");
            break;
        }

        if (opcion == 7) {
            // Display history
            System.out.println("\n--- HISTORIAL DE CONVERSIONES ---");
            if (historial.isEmpty()) {
                System.out.println("No hay conversiones recientes.");
            } else {
                historial.forEach(System.out::println); // Lambda!
            }
            System.out.println("---------------------------------\n");
            continue;
        }

        if (opcion >= 1 && opcion <= 6) {
            // Process conversion...
        } else {
            System.out.println("Opción no válida. Intente de nuevo.\n");
        }
    }
    sc.close();
}

System.out.println("Ingrese el valor que desea convertir: ");
double cantidad = sc.nextDouble();
double resultado;
String base = "", objetivo = "";

// Assign currencies based on option
objetivo = switch (opcion) {
    case 1 -> {
        base = "USD";
        yield "ARS";
    }
    case 2 -> {
        base = "ARS";
        yield "USD";
    }
    case 3 -> {
        base = "USD";
        yield "BRL";
    }
    case 4 -> {
        base = "BRL";
        yield "USD";
    }
    case 5 -> {
        base = "USD";
        yield "COP";
    }
    case 6 -> {
        base = "COP";
        yield "USD";
    }
    default -> objetivo;
};

// Use the service to get the rate
resultado = consulta.obtenerTasa(base, objetivo, cantidad);
System.out.println("El valor es: " + resultado + " [" + objetivo + "]\n");

// Save to history with current timestamp
RegistroConversion registro = new RegistroConversion(
    base, objetivo, cantidad, resultado, LocalDateTime.now()
);
historial.add(registro);

Key Features

Menu Options

Options 1-6: Currency conversions
Option 7: View history
Option 8: Exit application

Data Structures

Scanner for user input
ConsultaMoneda service instance
List<RegistroConversion> for history

Switch Expressions

Uses Java 14+ switch expressions with yield for cleaner code

Lambda Functions

Uses method reference System.out::println for history display

ConsultaMoneda (Service Class)

Package: lad.com.alura.conversormoneda.modelos Purpose: Service class responsible for communicating with ExchangeRate-API.

Class Definition

package lad.com.alura.conversormoneda.modelos;

import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;

public class ConsultaMoneda {
    // Instance method (not static)
    public double obtenerTasa(String monedaBase, 
                             String monedaObjetivo, 
                             double cantidad) {
        // Implementation
    }
}

obtenerTasa() Method Signature

monedaBase

String

required

Source currency code (e.g., “USD”, “ARS”, “BRL”)

monedaObjetivo

String

required

Target currency code (e.g., “ARS”, “BRL”, “COP”)

cantidad

double

required

Amount to convert

returns

double

Converted amount, or 0 if error occurs

Method Implementation Breakdown

Create HTTP Client

HttpClient cliente = HttpClient.newHttpClient();

Creates a new HTTP client for making requests

Build API URL

String url = "https://v6.exchangerate-api.com/v6/9ba310889b4d07769a662fc0/pair/" 
    + monedaBase + "/" + monedaObjetivo + "/" + cantidad;

Constructs the API endpoint with currency codes and amount

Create HTTP Request

HttpRequest request = HttpRequest.newBuilder()
        .uri(URI.create(url))
        .GET()
        .build();

Builds an HTTP GET request

Send Request

HttpResponse<String> respuesta = cliente.send(
    request, 
    HttpResponse.BodyHandlers.ofString()
);

Sends the request and receives response as String

Parse JSON

JsonElement elemento = JsonParser.parseString(respuesta.body());
JsonObject objectRoot = elemento.getAsJsonObject();

Parses JSON response into JsonObject

Extract Result

return objectRoot.get("conversion_result").getAsDouble();

Extracts and returns the conversion result

Handle Errors

catch (Exception e) {
    System.out.println("Error al conectar con la API: " + e.getMessage());
    return 0;
}

Catches all exceptions and returns 0

Usage Example

// Create service instance
ConsultaMoneda consulta = new ConsultaMoneda();

// Perform conversion
double resultado = consulta.obtenerTasa("USD", "ARS", 100.0);

// Display result
System.out.println("100 USD = " + resultado + " ARS");

The method is not static, following OOP principles. You must create an instance of ConsultaMoneda to use it.

RegistroConversion (Data Record)

Package: lad.com.alura.conversormoneda.modelos Purpose: Immutable data structure to store conversion history entries.

Record Definition

package lad.com.alura.conversormoneda.modelos;

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;

public record RegistroConversion(
    String monedaBase, 
    String monedaObjetivo, 
    double cantidad, 
    double resultado, 
    LocalDateTime fechaHora
) {
    @Override
    public String toString() {
        DateTimeFormatter formato = DateTimeFormatter.ofPattern("dd-MM-yyyy HH:mm:ss");
        return "[" + fechaHora.format(formato) + "] " 
            + cantidad + " " + monedaBase + " =>> " 
            + resultado + " " + monedaObjetivo;
    }
}

Record Components

monedaBase

String

The base (source) currency code

monedaObjetivo

String

The target (destination) currency code

cantidad

double

The original amount in base currency

resultado

double

The converted amount in target currency

fechaHora

LocalDateTime

Timestamp when the conversion was performed

Java Records (Java 14+)

What are Records?

Records are a special kind of class introduced in Java 14 that provide:

Automatic constructor
Automatic getters (component methods)
Automatic equals() and hashCode()
Automatic toString() (can be overridden)
Immutability by default

Automatically Generated Methods

Constructor
Getters
equals & hashCode

// Automatically generated canonical constructor
public RegistroConversion(
    String monedaBase,
    String monedaObjetivo,
    double cantidad,
    double resultado,
    LocalDateTime fechaHora
) {
    // Fields are automatically assigned
}

// Component accessor methods (automatically generated)
public String monedaBase() { return this.monedaBase; }
public String monedaObjetivo() { return this.monedaObjetivo; }
public double cantidad() { return this.cantidad; }
public double resultado() { return this.resultado; }
public LocalDateTime fechaHora() { return this.fechaHora; }

// Automatically generated based on all components
@Override
public boolean equals(Object obj) {
    // Compares all fields
}

@Override
public int hashCode() {
    // Hash based on all fields
}

Custom toString() Implementation

The record overrides toString() to provide formatted output:

@Override
public String toString() {
    DateTimeFormatter formato = DateTimeFormatter.ofPattern("dd-MM-yyyy HH:mm:ss");
    return "[" + fechaHora.format(formato) + "] " 
        + cantidad + " " + monedaBase + " =>> " 
        + resultado + " " + monedaObjetivo;
}

Example Output:

[05-03-2026 14:30:45] 100.0 USD =>> 6323.41 ARS

Usage Examples

// Create a new conversion record
RegistroConversion registro = new RegistroConversion(
    "USD",              // monedaBase
    "ARS",              // monedaObjetivo
    100.0,              // cantidad
    6323.41,            // resultado
    LocalDateTime.now() // fechaHora
);

Conversor (View Class)

Package: lad.com.alura.conversormoneda.vista Purpose: Handles user interface display and presentation logic.

Class Structure

package lad.com.alura.conversormoneda.vista;

public class Conversor {
    public static void eleccionUserMenu() {
        System.out.print("""
                Sea bienvenido/a al Conversor de Moneda =]
                
                ==================================================
                1) Dólar           =>> Peso argentino
                2) Peso argentino  =>> Dólar
                3) Dólar           =>> Real brasileño
                4) Real brasileño  =>> Dólar
                5) Dólar           =>> Peso colombiano
                6) Peso colombiano =>> Dólar
                7) Historial de conversiones
                8) Salir
                ==================================================
                Elija una opción válida:
                """);
    }
}

eleccionUserMenu() Method

parameters

none

No parameters required

returns

void

No return value (displays menu to console)

access

public static

Static method - can be called without creating an instance

Text Blocks (Java 13+)

The method uses text blocks for multi-line string literals:

Text Block Syntax
Traditional Syntax (Pre-Java 13)

System.out.print("""
    Multi-line
    String
    Content
    """);

Benefits:No need for \n newline characters, no need for string concatenation, preserves formatting and indentation, and more readable for large text blocks.

System.out.print(
    "Sea bienvenido/a al Conversor de Moneda =]\n" +
    "\n" +
    "==================================================\n" +
    "1) Dólar           =>> Peso argentino\n" +
    "2) Peso argentino  =>> Dólar\n" +
    // ... more lines
);

Drawbacks:Requires \n for each line, requires + concatenation, less readable, and more error-prone.

Option 1

USD → ARS (Dollar to Argentine Peso)

Option 2

ARS → USD (Argentine Peso to Dollar)

Option 3

USD → BRL (Dollar to Brazilian Real)

Option 4

BRL → USD (Brazilian Real to Dollar)

Option 5

USD → COP (Dollar to Colombian Peso)

Option 6

COP → USD (Colombian Peso to Dollar)

Option 7

Display conversion history

Option 8

Exit the application

Usage

// Call from controller
Conversor.eleccionUserMenu();

// User sees the menu and enters their choice
int opcion = scanner.nextInt();

The method uses System.out.print() (not println()) so the cursor remains on the same line as the prompt, providing a better user experience.

Method Signatures Summary

ConversorApp.main()

public static void main(String[] args)

Application entry point - orchestrates the entire conversion flow

ConsultaMoneda.obtenerTasa()

public double obtenerTasa(String monedaBase, String monedaObjetivo, double cantidad)

Performs API request and returns converted amount

RegistroConversion (Constructor)

public RegistroConversion(String monedaBase, String monedaObjetivo, 
                         double cantidad, double resultado, 
                         LocalDateTime fechaHora)

Creates immutable conversion history record

RegistroConversion.toString()

public String toString()

Returns formatted string representation of the conversion

Conversor.eleccionUserMenu()

public static void eleccionUserMenu()

Displays the main menu to the user

Modern Java Features Used

Records (Java 14+)

Used in RegistroConversion for immutable data carriers:

public record RegistroConversion(
    String monedaBase,
    String monedaObjetivo,
    double cantidad,
    double resultado,
    LocalDateTime fechaHora
) { }

Text Blocks (Java 13+)

Used in Conversor.eleccionUserMenu() for multi-line strings:

System.out.print("""
    Multi-line
    String
    """);

Switch Expressions (Java 14+)

Used in ConversorApp.main() for currency selection:

objetivo = switch (opcion) {
    case 1 -> {
        base = "USD";
        yield "ARS";
    }
    // ...
};

Lambda Expressions (Java 8+)

Used for history display:

historial.forEach(System.out::println);

HttpClient (Java 11+)

Modern HTTP client API:

HttpClient cliente = HttpClient.newHttpClient();
HttpResponse<String> respuesta = cliente.send(request, 
    HttpResponse.BodyHandlers.ofString());

var Keyword (Java 10+)

While not used in this codebase, could simplify local variable declarations:

var consulta = new ConsultaMoneda();
var historial = new ArrayList<RegistroConversion>();

Java Version Requirement: This application requires Java 14 or higher due to the use of records and switch expressions with yield.

Dependencies

Standard Library
External Libraries

java.net.http.HttpClient - HTTP communication
java.net.URI - URL handling
java.time.LocalDateTime - Timestamp management
java.time.format.DateTimeFormatter - Date formatting
java.util.Scanner - User input
java.util.ArrayList - Dynamic list storage
java.util.List - List interface

Gson 2.10.1+ (com.google.code.gson)
- JsonParser - Parse JSON strings
- JsonElement - JSON element representation
- JsonObject - JSON object access

Getting Started

User Guide

Technical Reference

Development

​Overview

​ConversorApp (Main Controller)

​Class Structure

​main() Method

​Complete Implementation

​Key Features

Menu Options

Data Structures

Switch Expressions

Lambda Functions

​ConsultaMoneda (Service Class)

​Class Definition

​obtenerTasa() Method Signature

​Method Implementation Breakdown

​Usage Example

​RegistroConversion (Data Record)

​Record Definition

​Record Components

​Java Records (Java 14+)

What are Records?

​Automatically Generated Methods

​Custom toString() Implementation

​Usage Examples

​Conversor (View Class)

​Class Structure

​eleccionUserMenu() Method

​Text Blocks (Java 13+)

​Menu Options

Option 1

Option 2

Option 3

Option 4

Option 5

Option 6

Option 7

Option 8

​Usage

​Method Signatures Summary

ConversorApp.main()

ConsultaMoneda.obtenerTasa()

RegistroConversion (Constructor)

RegistroConversion.toString()

Conversor.eleccionUserMenu()

​Modern Java Features Used

​Dependencies

Build docs developers (and LLMs) love

Overview

ConversorApp (Main Controller)

Class Structure

main() Method

Complete Implementation

Key Features

ConsultaMoneda (Service Class)

Class Definition

obtenerTasa() Method Signature

Method Implementation Breakdown

Usage Example

RegistroConversion (Data Record)

Record Definition

Record Components

Java Records (Java 14+)

Automatically Generated Methods

Custom toString() Implementation

Usage Examples

Conversor (View Class)

Class Structure

eleccionUserMenu() Method

Text Blocks (Java 13+)

Menu Options

Usage

Method Signatures Summary

Modern Java Features Used

Dependencies