If statement terminates after entering incorrect math expression, but continues to work after correct expression

First of all, thanks Eran and T.J. Crowder for pointing out my mistake but I have a different problem now.

    Scanner scan = new Scanner (System.in);
    int sum, HighRes, LowRes, Agg, Ave, Amount, Wrong, Right;
    String operator, another = "y", num1, num2;
    HighRes = 0;
    LowRes = 0;
    Agg = 0;
    Amount = 0;
    DecimalFormat df = new DecimalFormat("#.00"); 
    Wrong = 0;
    Right = 0;


    while (another.equalsIgnoreCase("y"))
            {
            System.out.println("Enter the first number, second number and the operator (+, -, * or /)");
            num1 = scan.next();
            num2 = scan.next();       
            operator =scan.next();
            System.out.println( "Expression is " + num1 + " " +num2 + " " +operator);

            if (num1.equals("-") || num1.equals("+") || num1.equals("*") || num1.equals("/") || num1.equals("<<") || num1.equals(">>") || num1.equals("%") || num1.equals("&") || num1.equals("|") ||num2.equals("-") || num2.equals("+") || num2.equals("*") || num2.equals("/") || num2.equals("<<") || num2.equals(">>") || num2.equals("%") || num2.equals("&") || num2.equals("|")) {
                System.out.println("Invalid expression");
                System.out.print ("Test another expression (Type Y if yes and leave empty if no?) ");
                another = scan.nextLine();
                Wrong++;
            }
            else if  (num1 != "-"  || num1 != "+" || num1 != "*" || num1 != "/" || num2 != "+" || num2 != "+" || num2 != "+" || num2 != "+") {    
                int num3 = Integer.parseInt(num1);
                int num4 = Integer.parseInt(num2);
                        if (num3 > -1000000000 && num3 < 1000000000 && num4 > -1000000000 && num4 < 1000000000){

                                 if (operator.equals("+")) {
                                        sum = num3 + num4;
                                        System.out.println ("" + num3 + " " + operator + " " + num2 + " = " + sum);
                                        System.out.print ("Test another expression (Type Y if yes and leave empty if no?) ");
                                    another = scan.nextLine();
                                    Agg = Agg + sum;
                                    Amount++;
                                    Right++;
                                    if (sum > HighRes) {
                                        HighRes = sum;
                                    }
                                    if (sum < LowRes){
                                        LowRes = sum;
                                    }
                                }
                                else if (operator.equals("-")) {
                                        sum = num3 - num4;
                                        System.out.println ("" + num3 + " " + operator + " " + num2 + " = " + sum);
                                        System.out.print ("Test another expression (Type Y if yes and leave empty if no?) ");
                                    another = scan.nextLine();
                                    Agg = Agg + sum;
                                    Amount++;
                                    Right++;
                                    if (sum > HighRes) {
                                        HighRes = sum;
                                    }
                                    if (sum < LowRes){
                                        LowRes = sum;
                                    }
                                }

This is my code from my previous question, I no longer get an error, but, when I enter a correct expression, program continues to run and asks if I want to enter another expression. Correct But, when I enter incorrect one, it displays that it's incorrect and asks for a new expression but it immediately terminates.Incorrect (Evaluation is at the end of the program)

Edit: It's not the problem with the "else if", it's the "if" that does not wait for the response to the question if I want to test another expression.