java - 不确定我在这里做错了什么( boolean 标志)

Question

这是我的作业代码片段。我似乎无法让 boolean 标志正常工作。当我试图弄清楚时，要么每个名字都得到折扣，要么没有名字得到折扣。为了澄清名字迈克或戴安娜应该给予折扣。

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

首先，为了比较字符串，您不使用==。您需要使用 String#equals() 方法，如 per this SO question .

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

将被替换为

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

但是，如 Gavin在对原始问题的评论中说，最好将整个字符串转换为大写或小写，以减少比较。或者，按照Pshemo的注释，请使用 equalsIgnoreCase()。

您还需要更改:

if (discount = true)

即将 true 值赋给变量 discount，以

if (discount == true)

或者，按照Pshemo的评论，

if (discount)