Hello, I am stuck as to what to do from here in this hopefully simple prog

Question

I am trying to write a program that the user can enter any number in any unit of these (seconds, minutes, hours, centihours, or years). Then it should ask what to convert it into then the user could choose to convert it to seconds, minutes,hours, centihours, or years.
Any ideas?
This is what I have so far but I am stuck as to what to do from here:
import javax.swing.JOptionPane;
public class converttime{
public static void main (String[] args){
double inputNum = Double.parseDouble(JOptionPane.showInputDialog(null,"Enter a number: "));
Sring unit = JOptionPane.showInputDialog(null,"What unit is the number entered in? ");
String convert = JOptionPane.showInputDialog(null, "Do you want this converted into seconds, minutes, hours, centihours, or years?");
}

Answer 1

The least complicated way IMO is to write a series of if/elses. Something like this (pseudocode):
if (unit is seconds) {
    if (convert is minutes) {
        apply second-minutes conversion factor
    else if (convert is hours) {
        apply second-hours conversion factor
    etc...
else if (unit is minutes) {
    if (convert is seconds) {
        apply minutes-seconds conversion factor
    else if (convert is hours) {
        apply minutes-hours conversion factor
    etc...
etc...You should define the conversion factors as constants, and use the String.equals(String) method to compare Strings.
There are more clever ways to do it, but if you're a beginner, this may be easiest.