How to create a conversion of Fahrenheit to Celsius in java

The code should output a table for Fahrenheit and Celsius:

public static void main(String[] args) {
    System.out.println("Fahrenheit\tCelsius");
    System.out.println("=======================");
     for(int temp = -45; temp <= 120; temp += 5) //for(int i = 0; i <= 100; i+= 10)
        {
            System.out.printf("%5d       |", temp);
            double sum = (temp + (9.0/5.0)) * 32;   
            System.out.printf("%5d", (int) sum );
            System.out.println();
        }
}

Solution

How to create a conversion of Fahrenheit to Celsius in java

The most important step IMHO is to understand the problem before ever thinking about coding.

Wikipedia is a good start and searching for Celsius it give us:

[°C] = ([°F] − 32) × 5⁄9

In Java that would be something like:

celsius = (fahrenheit -32.0) * 5.0 / 9.0;

I think it is best to do that in a separate method so it is easier to test it:

public static double fahrenheitToCelsius(double fahrenheit) {
    double celsius = (fahrenheit - 32.0) * 5.0 / 9.0;
    return celsius;
}

Note 1: it is worth testing this method before going on - two significant temperatures are:

32°F == 0°C (melting point of ice)
212°F == 100°C (boiling point of water)

so just do something quick & dirty like:

System.out.println("32 == " + fahrenheitToCelsius(32));
System.out.println("212 == " + fahrenheitToCelsius(212));

much better, maybe a bit to heavy in that simple case, is to use some framework like JUnit.

Note 2: for creating the table do as posted in the question, but only one printf to take advantage of having the format together at one place (obviously after calling above method):

System.out.printf("%5.0f | %5.1f\n", fahrenheit, celsius);

Note 3: caution with 5/9 - in Java that is interpreted as integer division and would result in zero!

(above code is just a sample and was not tested or debugged