do-while循环中变量的范围

Question

如果用户在程序末尾提示时输入“ y”或“ Y”，我试图遍历整个程序，但是由于变量，我收到“找不到符号-变量响应”错误我声明在do-while循环内，因此我想我不能在do-while循环的情况下使用它。 如果用户输入“ y”或“ Y”，是否有任何方法可以解决此问题，并且仍然可以遍历该程序？ 这一切都在main方法中，而getFileRunStats是包含程序中所有其他方法的方法。

以下是相关代码：

public static void main(String[] args) throws IOException {
    System.out.println("A program to analyze home field advantage in sports.");
    System.out.println();        
    Scanner keyboard = new Scanner(System.in);

do{   
    getFileRunStats(keyboard);

    System.out.println("Do you want to check another data set?");
    System.out.print("Enter Y or y for to analyze another file, anything else to quit: ");
    String response = keyboard.nextLine();
}while(response == "Y" || response == "y");


}

Answer 1

您只需删除该语句，然后将其添加到循环条件中即可。

do {
} while (keyboard.nextLine().equalsIgnoreCase("y"));

Answer 2

@ergonaut的回答是针对您的确切问题的最佳解决方案：

您只需删除该语句，然后将其添加到循环条件中即可。

do {

} while (keyboard.nextLine().equalsIgnoreCase("y"));

请注意，代码还通过使用equals方法而不是==运算符解决了您遇到的错误 。

---

但是，对于如何使用循环内定义的值控制do-while循环的更通用解决方案，您有两种选择：

// Define variable outside, no need to initialize it
String response;
do {
    // code here
    response = keyboard.nextLine();
} while (response.equals("Y") || response.equals("y"));

// Use break inside an infinite loop
for (;;) { // or   while (true) { ... }   or   do { ... } while (true)
    // code here
    String response = keyboard.nextLine();
    if (! response.equals("Y") && ! response.equals("y"))
        break;
}

Answer 3

只是为您的问题提供了一种更可扩展的方法，因为它允许您将来向程序中动态添加更多选项。

public static void main(String[] args) {
    System.out.println("A program to analyze home field advantage in sports.");
    System.out.println();
    Scanner keyboard = new Scanner(System.in);

    boolean quit = false;
    do{
        System.out.println("Do you want to check another data set?");
        System.out.print("Enter Y or y for to analyze another file ");
        System.out.print("Enter X to do X");
        System.out.print("Enter Z to do Z");
        String response = getUserInput(keyboard);

        if (response.equalsIgnoreCase("X"))
            doX();
        else if (response.equalsIgnoreCase("Y"))
            doY();
        else if (response.equalsIgnoreCase("Z"))
            doZ();
        else
            quit = true;

    }while(!quit);
}

private static String getUserInput(Scanner scanner) {
    return scanner.nextLine();
}

private static void doX() {
    System.out.println("X");
}

private static void doY() {
    System.out.println("Y");
}

private static void doZ() {
    System.out.println("Z");
}

}

Answer 4

只需在do-while循环外声明“ response”变量，如下所示：

String reponse = null;
do{   
    getFileRunStats(keyboard);

    System.out.println("Do you want to check another data set?");
    System.out.print("Enter Y or y for to analyze another file, anything else to quit: ");
    response = keyboard.nextLine();
}while(response == "Y" || response == "y");


}