My computer doesn't process if statements after some point [duplicate]

I wrote this code

import java.util.*;

 // Compiler version JDK 11.0.2
 import java.util.Scanner;

 class Dcoder
 {
   public static void main(String args[])
   { 
     Scanner sc = new Scanner(System.in);
     int whole =0;
     int secondWhole=0;
     int num1=0;
     int num2=0;
     int secondNum1=0;
     int secondNum2=0;
     int result=0;
     int choice=0;
     int choice2=0; 
     int step=0;
     int max=0;
     int lcm=0;
     int mu1=0;
     int mu2=0;
     int di1=0;
     int di2=0;
    System.out.println("press 1 if the first num is mixed and 2  if proper fraction");
    choice = sc.nextInt();
    System.out.println("press 1 if the second num is mixed and 2  if proper fraction");
    choice2 = sc.nextInt();
    if(choice == 1 && choice2 == 1){
      System.out.println("enter the whole num");
      whole = sc.nextInt();
      System.out.println("enter the num1(numerator)");
      num1 = sc.nextInt();
      System.out.println("enter the num2(denominator)");
      num2 = sc.nextInt();
      int num3 = (whole*num2)+num1;
      
      System.out.println("enter the second whole num");
      secondWhole = sc.nextInt();
      System.out.println("enter the second num1(numerator)");
      secondNum1 = sc.nextInt();
      System.out.println("enter the scond num2(denominator)");
      secondNum2 = sc.nextInt();
      int num4 = (secondWhole*secondNum2)+secondNum1;
      
      
        if(num2 > secondNum2){
         max =  step = num2;
      }
      else if(num3<num4){
         max = step = secondNum2;
      }

      while(num3!= 0) {
         if( max % num2 == 0 && max % secondNum2 == 0) {
            lcm = max;
            break;
         }
         max += step;
      }
      System.out.println("what do you want to do(+/-)");
      String Expression = sc.nextLine();
      if(Expression == "+"){

      di1 =lcm/num2;
      mu1 =di1*num3;
      di2 =lcm/secondNum2;
      mu2 =di2*num4;
      result = mu1 +mu2;
      
      }
else if(Expression == "-"){
       di1 =lcm/num2;
      mu1 =di1*num3;
      di2 =lcm/secondNum2;
      mu2 =di2*num4;
      result = mu1 -mu2;
      
      
      }
      System.out.println("result = "+result+"/"+lcm);
    }
   }
 }

The computer doesn't process this

if(Expression == "+"){

      di1 =lcm/num2;
      mu1 =di1*num3;
      di2 =lcm/secondNum2;
      mu2 =di2*num4;
      result = mu1 +mu2;

      }
else if(Expression == "-"){
       di1 =lcm/num2;
      mu1 =di1*num3;
      di2 =lcm/secondNum2;
      mu2 =di2*num4;
      result = mu1 -mu2;

But shows the result yeah it's wrong It's shows this

press 1 if the first num is mixed and 2  if proper fraction
1
press 1 if the second num is mixed and 2  if proper fraction
1
enter the whole num
2
enter the num1(numerator)
1
enter the num2(denominator)
3
enter the second whole num
3
enter the second num1(numerator)
1
enter the scond num2(denominator)
5
what do you want to do(+/-)
result = 0/15

Process finished.

Please help