不知道我在做什么错（布尔标志）

Question

Here's a snippet of my code for an assignment. I can't seem to get the boolean flag to work properly. When i try to figure it out, either every name gets the discount or no name gets the discount. To clarify the name Mike or Diana should give a discount.

String firstName;     //user's first name  
boolean discount = false;  //flag, true if user is eligible for discount 
int inches;       //size of the pizza
char crustType;     //code for type of crust
String crust; //name of crust
double cost = 12.99;    //cost of the pizza
final double TAX_RATE = .08; //sales tax rate
double tax;       //amount of tax
char choice;      //user's choice
String input;      //user input
String toppings = "Cheese "; //list of toppings 
int numberOfToppings = 0;  //number of toppings

//prompt user and get first name
System.out.println("Welcome to Mike and Diane's Pizza");
System.out.print("Enter your first name:  ");
firstName = keyboard.nextLine();

if (firstName == "mike" || firstName == "diana" || firstName == "Mike" || firstName == "Diana" ||
firstName == "MIKE" || firstName == "DIANA")
{
discount = true;
}

if (discount = true)
{
cost  -= 2.0;
System.out.println ("You are eligible for a $2 discount.");

Answer 1

First of all, in order to compare Strings, you don't use == . You need to use the String#equals() method as per this SO question .

if (firstName == "mike" || firstName == "diana" || firstName == "Mike" || firstName == "Diana" || firstName == "MIKE" || firstName == "DIANA")

would be replaced by

if (firstName.equals("mike") || firstName.equals("diana") || firstName.equals("Mike") || firstName.equals("Diana") || firstName.equals("MIKE") || firstName.equals("DIANA"))

However, as Gavin says in the comments to your original question, it would be better to convert entire string to either uppercase or lowercase, to make less comparaisons. Or, as per Pshemo 's comment, use equalsIgnoreCase() .

You also need to change:

if (discount = true)

which is assigning the value of true to the variable discount , to

if (discount == true)

or, as per Pshemo 's comment,

if (discount)

Answer 2

I've checked your code with my eclipse. Using

if(firstName == "mike" || firstName == "diana" || firstName == "Mike" || firstName == "Diana" ||firstName == "MIKE" || firstName == "DIANA")

is the problem, because of problems when comparing strings like this. You must have to change it to

if (firstName.equals("mike")){
    discount = true;
}

Then keep in mind that discount is a boolean variable. So you dont have to compare as whether it's true or not.

if (discount) //if will check whether it's true or not if provided with a condition,discount is boolean, so need of comparison

will be very simple for boolean operator.