Java Program to Convert Fahrenheit to Celsius

In this tutorial, you will learn how to write a Java program to convert Fahrenheit to Celsius. We will break this down into three steps:

Understanding the formula used for temperature conversion.
Writing a basic program using a predefined Fahrenheit value.
Making it interactive by accepting user input via the Scanner class.

Fahrenheit to Celsius Conversion

Fahrenheit and Celsius are two commonly used temperature scales. To convert a temperature from Fahrenheit to Celsius, we use the following formula:

Celsius = (Fahrenheit − 32) × 5 / 9

Where:

Fahrenheit represents the temperature in Fahrenheit.
Celsius represents the converted temperature in Celsius.
32 is subtracted as part of the Fahrenheit-to-Celsius conversion formula.
5/9 is the conversion factor between the two temperature scales.

Example:

Let’s consider an example where the temperature is 98.6°F. We can convert it into Celsius using the formula:

Celsius = (98.6 − 32) × 5 / 9
= 66.6 × 5 / 9
= 37°C

Therefore, 98.6°F is equal to 37°C.

Java Program to Convert Fahrenheit to Celsius

Problem Statement: Write a Java program to convert a temperature from Fahrenheit to Celsius by assigning a predefined value directly to a variable.

Complete Java Program

/**
 * Java Program to Convert Fahrenheit to Celsius
 */
public class FahrenheitToCelsius {
    public static void main(String[] args) {
        // Declare and initialize the temperature in Fahrenheit using a double
        // to accurately handle decimal values (e.g., 98.6°F).
        double fahrenheit = 98.6;

        // Convert Fahrenheit to Celsius using the standard formula: C = (F - 32) * (5 / 9).
        // Note: Using 5.0 / 9.0 ensures floating-point division and avoids integer truncation.
        double celsius = (fahrenheit - 32) * 5.0 / 9.0;

        // Display the converted temperatures on the console.
        System.out.println("Temperature in Fahrenheit: " + fahrenheit + "°F");
        System.out.println("Temperature in Celsius: " + celsius + "°C");
    }
}

Expected Output:

Temperature in Fahrenheit: 98.6°F
Temperature in Celsius: 37.0°C

In this Java program:

We have created a public class named FahrenheitToCelsius, which encapsulates the program.
Then, we have declared a main method, which serves as the entry point of the Java application. The main() method is the starting point of the program execution.
After that, we declared a variable named fahrenheit of type double to store the temperature in Fahrenheit. The double data type is used to accurately handle fractional (decimal) values.
The expression (fahrenheit – 32) * 5 / 9 converts Fahrenheit into Celsius and stores the resulting temperature in the celsius variable.
The statement System.out.println() displays the Fahrenheit and Celsius temperatures on the console.

The most important statement in the program is:

double celsius = (fahrenheit - 32) * 5 / 9;

This statement applies the Fahrenheit-to-Celsius conversion formula and stores the result in the celsius variable.

Java Program to Convert Fahrenheit to Celsius Using Scanner

Problem Statement: Write an interactive Java program to accept a temperature in Fahrenheit from the user using the Scanner class, pass it to a user-defined instance method to perform the calculation, and display the converted Celsius temperature.

Complete Java Program

/**
 * Java Program to Convert Fahrenheit to Celsius using Scanner class.
 */
import java.util.Scanner;

public class FahrenheitToCelsiusConverter {
    // User-defined instance method to convert Fahrenheit to Celsius
    public double convertToCelsius(double fahrenheit) {
        return (fahrenheit - 32) * 5 / 9;
    }

    public static void main(String[] args) {
        // Create a Scanner object to read input from the user
        Scanner scanner = new Scanner(System.in);

        // Prompt the user to enter the temperature in Fahrenheit
        System.out.print("Enter temperature in Fahrenheit: ");
        double fahrenheit = scanner.nextDouble();

        // Create an instance of the class to call the instance method
        FahrenheitToCelsiusConverter converter = new FahrenheitToCelsiusConverter();

        // Call the user-defined instance method
        double celsius = converter.convertToCelsius(fahrenheit);

        // Display the results
        System.out.println("Temperature in Fahrenheit: " + fahrenheit + "°F");
        System.out.println("Temperature in Celsius: " + celsius + "°C");

        // Close the scanner resource to prevent memory leaks
        scanner.close();
    }
}

Expected Output:

Enter temperature in Fahrenheit: 98.6 
Temperature in Fahrenheit: 98.6°F 
Temperature in Celsius: 37.0°C

In this Java program:

The statement import java.util.Scanner; imports the Scanner class for reading input from the keyboard.
A Scanner object is created to accept the Fahrenheit temperature from the user.
The convertToCelsius() user-defined instance method accepts the Fahrenheit temperature as a parameter.
The method applies the formula (fahrenheit – 32) * 5 / 9 and returns the calculated Celsius value.
An object of the FahrenheitToCelsiusConverter class is created to call the instance method.
The nextDouble() method reads a decimal or numeric value entered by the user.
The converted Celsius temperature is stored in the celsius variable.
System.out.println() displays the Fahrenheit and Celsius temperatures.
scanner.close() closes the Scanner resource to free up memory.

Key Points to Remember

The Fahrenheit-to-Celsius formula is Celsius = (Fahrenheit − 32) × 5 / 9.
Use the double data type when the temperature can contain decimal values.
The Scanner class can be used to accept temperature input dynamically from the user.
The nextDouble() method reads a numeric or decimal value entered by the user.