Diving Calculator - Please Help!

[terripwilliams]

I am supposed to be making a program to help divers calculate things. I have made methods to calculate a few different equations (I have only really just started) but i can't figure out how to call them to print the answer and things. here's my code I don't know what i'ev done wrong i've looked up a bunch of different things and this is what i've found but it isn't compiling.

import java.util.*;

public class Program
{
 
    double percentage;
    double pressure;
    double standard = 1.4;
    double depth;
    String input;
    
   
    
    public Program()
    {
        Scanner scan = new Scanner (System.in);
        
        System.out.println ("Which calculation do you wish to perform (Help/MOD/SMOD/BM/PP/EAD)? ");
        input = scan.nextLine();
        if (input == "mod" || input == "MOD") {
            System.out.println("Calculating the MOD");
            System.out.println("Enter the percentage of Oxygen: ");
            percentage = scan.nextDouble();
            System.out.println("Enter the partial pressure of Oxygen (between 1.1 and 1.6 inclusive): ");
            pressure = scan.nextDouble();
            System.out.println("Maximum Operation Depth for a dive with " + percentage + " with a partial pressure of " + pressure + " is " + printMOD() + " metres.");
        } else if (input == "smod" || "SMOD") {
            System.out.println("Calculating the SMOD");
            System.out.println("Calculating the MOD for the standard 1.4 partial pressure");
            System.out.println("Enter the percentage of Oxygen: ");
            percentage = scan.nextDouble();
            int result = printSMOD();
            System.out.println("Maximum Operation Depth for a dive with " + percentage + " with a partial pressure of " + pressure + " is " + result + " metres.");
        }
        
    }
    
    public static void printMOD() {
        int mod;       
        mod = ((pressure/percentage)-1)*10;
        return mod;
    }    
    
    public static void printSMOD (double percentage, double standard) {
        double smod;
        smod = ((1.4/percentage)-1)*10;
        return smod;
    }
    public static void printBM (double pressure, int depth) {
        double bm;
        bm = (pressure/depth)*100;
        return bm;
    }
}

[Fou-Lu]

Strings cannot be compared like this: if (input == "mod" || input == "MOD") {. This (and a similar one further down) must be written as if (input.equals("mod") || input.equals("MOD")){.