Temperature scale converter in Java

Question

I am creating this converter. There are three units that can be converted: kelvin, celcius and fahrenheit. I used two variables to check which unit is chosen. It's cek and cek2. Is there any way I can shorten this code, or I just have to add all possible combination using if statements as i am doing now?

 if (cek=="celcius"&&cek2=="celcius"){
  hasil.setText(nilai.getText());
  } //celcius ke celcius

  if (cek=="celcius"&&cek2=="fahrenheit"){
  double hasil1 = (nilai1*9/5)+32;
  String hasil2 =  String.valueOf(n.format(hasil1));
  hasil.setText(hasil2);
  }

  if (cek=="celcius"&&cek2=="kelvin"){
  double hasil1 = nilai1+273.15;
  String hasil2 =  String.valueOf(n.format(hasil1));
  hasil.setText(hasil2);
  }

  if (cek=="fahrenheit"&&cek2=="celcius"){
  double hasil1 = (nilai1-32)*5/9;
  String hasil2 =  String.valueOf(n.format(hasil1));
  hasil.setText(hasil2);
  }
  ....................................

Answer 1

You can shorten that code by not converting the values directly, but rather use common intermediate representation. E.g. you could convert the incoming number first to celsius (not matter what source and destinations are) and then convert the intermediate representation to the target:

double inputTemperature = ... ;
double outputTemperature;
String inputUnit = ... ;
String outputUnit = ... ;
// input conversion if necessary
if (inputUnit.equals("fahrenheit")) {
    inputTemperature = fahrenheitToCelsius(inputTemperature);
}
if (inputUnit.equals("kelvin")) {
    inputTemperature = kelvinToCelsius(inputTemperature);
}
// output conversion:
if (outputUnit.equals("fahrenheit")) {
    inputTemperature = celsiusToFahrenheit(inputTemperature);
}
if (outputUnit.equals("kelvin")) {
    inputTemperature = celsiusToKelven(inputTemperature);
}

So only 4 if statements rather than 9.

P.S.: Please review https://stackoverflow.com/questions/513832/how-do-i-compare-strings-in-java

Answer 2

You should make your variable names easier to understand. Also, you should probably use enums.