Help: Program not doing what it's supposed to

[nevets04]

Code:

import java.util.*;
import java.lang.*;
class sub
{
    public static void main(String[] args)
    {
        String a = "1";
        String b = "2";
        String c = "3";
        String d = "4";
        String e = "5";
        String f = "6";
        String g = "7";
        Scanner sa1 = new Scanner(System.in);
        System.out.println("1) Encrypt");
        System.out.println("2) Encrypt");
        System.out.print("What do you want to do?: ");
        int ia1 = sa1.nextInt();
        if (ia1 == 1)
        {
            Scanner sa2 = new Scanner(System.in);
            System.out.print("What do you want to encrypt?: ");
            String ia2 = sa2.next();
            int ia2len = ia2.length();
            int cero = -1;            
            for (int loop = 0; loop < ia2len; loop++)
            {
                int cero1 = cero + 1;
                int cero2 = cero + 2;
                if (ia2.substring(cero1,cero2) == "a")
                    System.out.print(a);
                else if (ia2.substring(cero1,cero2) == "b")
                    System.out.print(b);
                else if (ia2.substring(cero1,cero2) == "c")
                    System.out.print(c);
                else if (ia2.substring(cero1,cero2) == "d")
                    System.out.print(d);
                else if (ia2.substring(cero1,cero2) == "e")
                    System.out.print(e);
                else if (ia2.substring(cero1,cero2) == "f")
                    System.out.print(f);
                else
                    System.out.print("no");
                System.out.println();
        
            }
        }    
    }
            
}

If I input 1, then I input a, it outputs "no"
I want it to output "1"
Does anyone see what is wrong?