Temperature Conversion Method Outputting Java

Question

I have to write a class called temperature and my only problem is when i try to call the conversion method. Whenever I run the main program, the conversion output is 0.0

Does it have something to do with using a private variable?

Code is below.

Many thanks!

public class Temperature {

private double temp;
private String scale;

public Temperature(double temp) {
    this.temp = temp;
}

public String toString () {
    return "your temp is " + this.temp;
}

public double getTemp() {
    return this.temp;
}

public String getScale(String scale) {
    this.scale = scale;
    return this.scale;
}

public double conversion() {
    double temp = 0;
    if (this.scale == "fahrenheit") {
        temp = (this.temp - 32) * (double)(5/9);
    }
    else if (this.scale == "celsius") {
        temp = (this.temp * (double)(9/5)) + 32;
    }
    return temp;
}

public boolean aboveBoiling(double temp) {
    if (this.scale == "fahrenheit") {
        return temp >= 212;
    }
    else if (this.scale == "celsius") {
        return temp >= 100;
    }
    return true;

}

}

below is my test driver to test function calls

import java.util.*;
public class testdriver {

public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);
    Temperature userTemp;
    String userScale;
    //userTemp = new Temperature(1.0);
    System.out.print("Please enter your temp scale(fahrenheit or celius): ");
    userScale = sc.next();
    System.out.println();

    System.out.print("Please enter your temp in " + userScale + ": ");
    userTemp = new Temperature(sc.nextDouble());
    System.out.println();

    System.out.println(userTemp.toString());
    System.out.println();

    System.out.println("your temp is: " + userTemp.getTemp());
    System.out.println();

    System.out.println("your scale is: " + userTemp.getScale(userScale));
    System.out.println();

    System.out.println(userTemp.conversion());
    System.out.println();

    double userTemp2 = userTemp.conversion();
    System.out.println(userTemp.aboveBoiling(userTemp2));







}

}

Answer 1

Replace this.scale == "fahrenheit" and this.scale == "celcius" by this.scale.equals("fahrenheit") and this.scale.equals("celcius"). In java, the == operator compare only references or primitive values (int, long, float, double...).

Edit: I found another problem in your code:

 (this.temp - 32) * (double)(5/9);

5 and 9 are integers, then the division will result in 0. You need to cast one of the operands to double, before the / operation:

 (this.temp - 32) * ((double)5/9);

or:

(this.temp - 32) * (5./9.);