在switchcase块中使用java

Question

我有一个问题，关于如何在开关盒内进行几次检查？在案例2中，我需要做一些检查，但是添加第二个if块，我的应用程序什么都不做，只是挂起。我错在哪里了

BufferedReader inputCommand = new BufferedReader(new InputStreamReader(System.in));

        while (true) {
                    System.out.println("Instruction:");
                    System.out.println();
                    System.out.println("1 -- Show all product at the store");
                    System.out.println("2 -- Add the product at the client basket");
                    System.out.println("3 -- Show client basket");
                    System.out.println();
                    switch (inputCommand.readLine()) {
                        case "1":
                            basketCommand.get();
                            System.out.println();
                            break;
                        case "2":
                            System.out.println();
                            System.out.println("Select product to add into your basket");
                            if (inputCommand.readLine().equals("su")){
                                basketCommand.addIntoBasket(productContainer.productList.get("su"));
                            }
                            if (inputCommand.readLine().equals("an")){
                                basketCommand.addIntoBasket(productContainer.productList.get("an"));
                            }
                            break;
    }

Answer 1

您的第一个if语句占用了输入行，因此第二个if语句没有任何内容可读

只需在阅读一次后存储该行：

                String readLine = inputCommand.readLine();

                if (readLine.equals("su")){
                    basketCommand.addIntoBasket(productContainer.productList.get("su"));
                }
                else if (readLine.equals("an")){
                    basketCommand.addIntoBasket(productContainer.productList.get("an"));
                }

Answer 2

每次执行inputCommand.readLine()时，程序都会等待您的输入。您不能像在本例中那样比较单个输入。最好的方法是将输入保存在变量中，然后执行检查。像这样的东西可以工作（未经测试）：

BufferedReader inputCommand = new BufferedReader(new InputStreamReader(System.in));
    while (true) {
                System.out.println("Instruction:");
                System.out.println();
                System.out.println("1 -- Show all product at the store");
                System.out.println("2 -- Add the product at the client basket");
                System.out.println("3 -- Show client basket");
                System.out.println();
                switch (inputCommand.readLine()) {
                    case "1":
                        basketCommand.get();
                        System.out.println();
                        break;
                    case "2":
                        System.out.println();
                        System.out.println("Select product to add into your basket");
                        String input = inputCommand.readLine();
                        if (input.equals("su")){
                            basketCommand.addIntoBasket(productContainer.productList.get("su"));
                        }
                        if (input.equals("an")){
                            basketCommand.addIntoBasket(productContainer.productList.get("an"));
                        }
                        break;
}

Answer 3

在第二个case语句中，您应该只读取下一个输入一次：

BufferedReader inputCommand = new BufferedReader(new InputStreamReader(System.in));

while (true) {
    System.out.println("Instruction:");
    System.out.println();
    System.out.println("1 -- Show all product at the store");
    System.out.println("2 -- Add the product at the client basket");
    System.out.println("3 -- Show client basket");
    System.out.println();
    switch (inputCommand.readLine()) {
    case "1":
        basketCommand.get();
        System.out.println();
        break;
    case "2":
        System.out.println();
        System.out.println("Select product to add into your basket");

        String next = inputCommand.readLine();
        if (next.equals("su")) {
            basketCommand.addIntoBasket(productContainer.productList.get("su"));
        }
        else if (next.equals("an")) {
            basketCommand.addIntoBasket(productContainer.productList.get("an"));
        }
        break;
    }
}

Answer 4

我假设这是一个用于学习目的的基本程序，所以我尽量保持简单

一,。别忘了关闭Scanner类

二,。始终将数字输入转换为小写（考虑“q”与“q”的情况）

三,。每次执行“scanner.nextLine（）”时，您的程序都将停止并等待来自源的输入（在这种情况下，System.in配置为从键盘获取输入）

四,。系统出来println将在输入结束时将“\n”打印到屏幕上，导致它创建新行，您可以在字符串中使用此字符保存代码行

完整代码：

import java.util.Scanner;
import java.io.IOException;

public class MyClass {

public static void ShowMenu()
{
      System.out.println("\nInstruction:");
      System.out.println("1 -- Show all product at the store");
      System.out.println("2 -- Add the product at the client basket");
      System.out.println("3 -- Show client basket");
      System.out.println("q -- Quit Program");


}

public static void ProductMenu()
{
      System.out.println("Select product to add into your basket");
      System.out.println();
      System.out.println("ba -- Basketball");
      System.out.println("fi -- Fiat 500");
      System.out.println("ip -- Iphone");
      System.out.println();
}

public static void Exit(Scanner sc) {
    sc.close();
    System.out.println("You've exited the program. goodbye!");
    System.exit(1);
}

public static void main(String args[]) {
    Scanner scanner = new Scanner(System.in);
    String inputCommand = null;

    while (true) {
       ShowMenu();
        switch (inputCommand = scanner.nextLine().toLowerCase()) {
            case "1":
                System.out.println("you entered 1");
                break;
            case "2":
                ProductMenu();
                inputCommand = scanner.nextLine(); //should block

                if (inputCommand.equals("ba")){
                    System.out.println("Basketball added.");
                }
                if (inputCommand.equals("fi")){
                    System.out.println("Fiat 500 added.");


                }
                if (inputCommand.equals("ip")){
                    System.out.println("Iphone added.");

                }
                break;

            case "q":
                Exit(scanner);
                break;
            default:
                System.out.println("Invalid Input");
                break;
        }
   }

}

}

Answer 5

用else if替换if

case "2":
     System.out.println();
     System.out.println("Select product to add into your basket");
     if (inputCommand.readLine().equals("su")){
        basketCommand.addIntoBasket(productContainer.productList.get("su"));
     }
     else if (inputCommand.readLine().equals("an")){
     basketCommand.addIntoBasket(productContainer.productList.get("an"));
     } 
     break;