java output for employee hours [duplicate]

I am trying to output the salary for each shift, but when outputted the salary shows up as 0.00 how can i correct this problem ? I have tried declaring the salary as float but i was unsuccessful ............................................................................................................

package overtime.pay;
import javax.swing.* ;
import java.util.Scanner;
/**
 *
 * @author whitneykenny
 */
public class OvertimePay {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
       
      Scanner Hours_worked = new Scanner(System.in);
    System.out.println("Enter how many hours worked ");
    int total_hours = Hours_worked.nextInt();
    
    if (total_hours == 40||total_hours < 40){
    
            System.out.println("Employee did not make any over time ");
   
    
    } else {
            
            System.out.println("The employee made overtime");
    
    
    }
    
   final double first_shift = 17.00;
       final double second_shift = 18.50;
       final double third_shift =  22.00;
    
            Scanner selected_shift = new Scanner(System.in);
    System.out.println("Which shift was worked  ");
    String shift_worked = selected_shift.nextLine();
            
         double salary = 0 ; 
        
        
if (shift_worked == "first") {
 salary =  first_shift;  
 
 
    }  else if (shift_worked == "second")  
    
    {salary = second_shift;
            
            }else if (shift_worked == "third")
            {
            
            }


System.out.println("Your salary is " + salary );

   
    
    
    
    }
            
            
            
            }