java - Scanner input validation in while loop

Question

I've got to show Scanner inputs in a while loop: the user has to insert inputs until he writes "quit". So, I've got to validate each input to check if he writes "quit". How can I do that?

while (!scanner.nextLine().equals("quit")) {
    System.out.println("Insert question code:");
    String question = scanner.nextLine();
    System.out.println("Insert answer code:");
    String answer = scanner.nextLine();

    service.storeResults(question, answer); // This stores given inputs on db
}

This doesn't work. How can I validate each user input?

Answer 1

问题是nextLine() “使扫描仪超过当前行”。nextLine()因此，当您调用while条件并且不保存返回值时，您已经丢失了用户输入的那一行。对第 3 行的调用nextLine()返回不同的行。

你可以试试这样的

    Scanner scanner=new Scanner(System.in);
    while (true) {
        System.out.println("Insert question code:");
        String question = scanner.nextLine();
        if(question.equals("quit")){
            break;
        }
        System.out.println("Insert answer code:");
        String answer = scanner.nextLine();
        if(answer.equals("quit")){
            break;
        }
        service.storeResults(question, answer);
    }

Answer 2

尝试：

while (scanner.hasNextLine()) {
    System.out.println("Insert question code:");
    String question = scanner.nextLine();
    if(question.equals("quit")){
     break;
    }

    System.out.println("Insert answer code:");
    String answer = scanner.nextLine();

    service.storeResults(question, answer); // This stores given inputs on db
}

Answer 3

始终检查scanner.nextLine是否没有“退出”

while (!scanner.nextLine().equals("quit")) {
    System.out.println("Insert question code:");
    String question = scanner.nextLine();
    if(question.equals("quit"))
     break;

    System.out.println("Insert answer code:");
    String answer = scanner.nextLine();
    if(answer.equals("quit"))
      break;

    service.storeResults(question, answer); // This stores given inputs on db 

}