Java：让程序在用户什么都不输入时不断提示用户输入

Question

I'm writing a program that asks for user input and keeps prompting the user for valid input if any of a few conditions aren't met. One such condition is that the input can't be an empty string. (ie the user typing nothing and just pressing Enter). How can I test for this? This is the code I have so far: (Note: the method isDateAcceptable isn't really relevant here because I want it to say "Number not acceptable." then re-prompt if the user enters ""). EDIT: I should add that with the current code, when a user enters an empty string the cursor just moves to the next line without ending the program.

public static String getNumOrDate(Scanner console){
    System.out.print("Enter a number or a date mm/dd/yyyy (-1 to exit):");
    String input = console.next();
    while(!input.equals("-1")) {
        if(input.isEmpty()){
            System.out.println("Number not acceptable.");
            getNumOrDate(console);
        }
        if (input.contains("/")) {
            while (!isDateAcceptable(input)) {
                System.out.println("Date not acceptable.");
                getNumOrDate(console);
            }
        } else if (canBeParsed(input)) {
            while (!isNumberAcceptable(input)) {
                System.out.println("Number not acceptable.");
                getNumOrDate(console);
            }
        }

    }
    System.out.println(isNumberAcceptable(input));
    return input;
}

public static boolean canBeParsed(String input){
    boolean parsable = true;
    try{
        Integer.parseInt(input);
    }catch(NumberFormatException e){
        parsable = false;
    }
    return parsable;
}
public static boolean isNumberAcceptable (String s){
    boolean isAcceptable = true;
    int numDigits = s.length();
    if(s.isEmpty()&& s == null){
        isAcceptable = false;
    }
    for(int i = 0; i < numDigits; i++){
        if(!Character.isDigit(s.charAt(i))){
            isAcceptable = false;
            break;
        }
    }

    if(isAcceptable){
        int number = Integer.parseInt(s);
        if((number < 1 && number != -1) || number > MAX_NUMBER){
            isAcceptable = false;
        }
    }
    return isAcceptable;
}

Answer 1

我建议您创建一个新的JFrame窗口并将一个输入字段和一个按钮拖到该窗口中。选择该按钮并在其上添加一个事件。然后您可以使用getText（）方法生成字符串，并检查其是否为“”如果满足您的要求，则可以关闭Jframe（如果没有），它将仍然保持打开状态。