正確使用Switch？菜單選項訂購三明治或沙拉

Question

早上好/下午，

以下是我爲我的Java課（如在學校作業）所寫的代碼。我不是在這裏試圖讓某人爲我做作業。

我的問題是：可以使用開關/外殼如何設置它？ 提示用戶輸入1或2.答案1他們得到一個三明治，回答2他們得到一份沙拉。

對這一計劃的說明與客戶開始將訂購三明治或沙拉。然後繼續添加配料以獲得額外費用，並可以減少額外的配料。然後打印出訂單和總量。教授指定使用IF語句和Switch。然而，我有一種感覺，我錯過了一些東西，因爲它看起來像是我在Stack上找到的例子中的IF代替語句。感謝您的幫助！

import java.util.Scanner; 

//loaded scanner to take user input 
public class Restaurant 


//dude change this, do 3 outputs asking for input 1 input 2 input 3 make those if statements after 
{ 
/* Author: 
    Date: 
    Program: create a class that will offer a sandwich for $7.00 with optional three 
    toppings lettuce, tomato, cheese $1.00 each 
    or a salad with optional two toppings tomatos, cheese $0.50 each. 
*/ 
    public static void main(String[] args) 

    { 

    // Declarations sandwich,salad,Sandwich-cheese,Sandwich-tomato,Sandwich-lettuce, salad-cheese, salad-tomato. 
     double sandwich = 7.00; 
     double salad = 7.00; 
     double sandChe = 1.00; 
     double sandTom = 1.00; 
     double sandLet = 1.00; 
     double salChe = .50; 
     double salTom = .50; 
     int userInput; 
     int userInput1; 
     int userInput2; 
     int userInput3; 
     double sandTotal; 
     double saladTotal; 

     Scanner scanner = new Scanner(System.in); 

     System.out.println("Enter 1 for a Sandwich or 2 for a Salad"); 
     int userInput = scanner.nextLine(); 

     switch(userInput) 
     { 
     case 1: // a sandwich was ordered 




      System.out.println("Enter 1 for additional topping of lettuce or press 2"); 
      int userInput1 = scanner.nextLine(); 


      System.out.println("Enter 1 for additional topping of cheese or press 2"); 
      int userInput2 = scanner.nextLine(); 


      System.out.println("Enter 1 for additional topping of tomato or press 2"); 
      int userInput3 = scanner.nextLine(); 



      if (userInput1 == 1 && userInput2 == 1 && userInput3 == 1) 
      { 
       saladTotal = (sandwich + sandLet + sandChe + sandTom); 
       System.out.println("Your bill comes to a total of: " + sandTotal + " Thank you, Have a great day!"); 



       if (userInput1 == 1 && userInput2 == 2 && userInput3 == 2) 
       { 
        sandTotal = (sandwich + sandLet); 
        System.out.println("Your bill for a salad with additional tomato toppings comes too: " + sandTotal + " Thank you, Have a great day!"); 


        if (userInput1 == 1 && userInput2 == 1 && userInput3 == 2) 
        { 
        sandTotal = (sandwich + sandLet + sandChe); 
        System.out.println("Your bill for a salad with no additional toppings comes too: " + salad + " Thank you, Have a great day!"); 


        if (userInput1 == 1 && userInput2 == 2 && userInput3 == 1) 
        { 
         sandTotal = (sandwich + sandLet + sandTom); 
         System.out.println("Your bill for a sandwich `enter code here`lettuce and tomato comes too: " + sandTotal + " Thank you, Have a great day!");  


         if (userInput1 == 2 && userInput2 == 1 && userInput == 1) 
         { 
          sandTotal = (sandwich + sandChe + sandTom); 
          System.out.println("Your bill for a sandwich with cheese and tomato comes too: " + sandTotal + " Thank you, Have a great day!"); 


          if (userInput1 == 2 && userInput2 == 2 && userInput3 == 2) 
          { 
           System.out.println("Your bill for a sandwich comes too: " + sandwich + " Thank you, Have a great day!"); 
          }// end if 1 
         }//end if 2 
        }//end if 3 
        }//end if 4 
       }//end if 5 
      }//end if 6 

     } 
    } 
}    


     // switch case below 


     case 2: // a salad was ordered 




      { 
       System.out.println("Press 1 for additional topping of cheese or press 2"); 
       int userInput1 = scanner.nextLine(); 



       System.out.println("Press 1 for additional topping of tomato or press 2"); 
       int userInput2 = scanner.nextLine(); 


       if (userInput1 == 1 && userInput2 == 2) 
       { 
        saladTotal = (salad + salChe); 
        System.out.println("Your bill comes to a total of: " + saladTotal + " Thank you, Have a great day!"); 



        if (userInput1 == 2 && userInput2 == 1) 
        { 
        saladTotal = (salad + salTom); 
        System.out.println("Your bill for a salad with additional tomato toppings comes too: " + saladTotal + " Thank you, Have a great day!"); 


        if (userInput1 == 2 && userInput2 == 2) 
        { 
         System.out.println("Your bill for a salad with no additional toppings comes too: " + salad + " Thank you, Have a great day!"); 


         if (userInput1 == 1 && userInput2 == 1) 

         { 
          saladTotal = (salad + salChe + salTom); 
          System.out.println("Your bill for a salad with Tomato and Cheese toppings comes too: " + saladTotal + " Thank you, Have a great day!"); 

         }//end if 1 
        }//end if 2 
        }//end if 3 
       }//end if 4 


      } 



}// end of class 

Answer 1

通常，switch-case語句和if/else塊是可以互換的。由於使用break（下面的例子），開關情況有點不同。儘管在大多數情況下使用if語句。我通常使用switch-case來處理基於枚舉的個案。

假設我們有一個枚舉食物類型：

public enum FoodType { 
    SANDWITCH, 
    SALAD, 
    FRUIT 
} 

所以，如果我想根據他選擇哪些食物詢問用戶的問題，我可能會做這樣的事情：

FoodType chosenType = FoodType.SANDWITCH; // can be user input 

switch (chosenType) { 
case SANDWITCH: 
    System.out.println("you want cheese?"); 
case SALAD: 
    System.out.println("Sauce?"); 
    break; 
case FRUIT: 
    System.out.println("which one?"); 
    break; 
default: 
    throw new IllegalStateException(); 
} 

請注意：

• 當選擇SANDWITCH時，問題是否想要奶酪？和'醬？'被打印，因爲沒有break聲明。
• 選擇FRUIT時，只有'哪一個？'將被打印。
• default會發生，如果用戶選擇了別的東西，這不是SANDWITCH或SALAD或FRUIT。

  if (FoodType.SALAD.equals(chosenType)) {...} 
  

  當有少數情況下，我會評估者如果語句使用簡單：

你當然可以用if語句以及寫這個。此外，「案例」中的代碼不應過長/複雜。我想如果你想知道什麼時候使用哪種語句;有確定的一些非常好的博客文章或stackoverflow的答案。

//旁註：我知道在示例中default:是不可達的代碼。