扫描仪的空白输入-Java [英] Blank input from scanner - java

问题描述

我想做的是，如果用户单击Enter键，则程序应引发BadUserInputException. 我的问题是，每当我按Enter键时，它只会使我进入控制台的另一行，而实际上什么也没做.

What I'm trying to do is if the user clicks on the enter key the program should throw a BadUserInputException. My problem is whenever I press the enter key it just puts me in another line in the console essentially doing nothing.

Scanner input = new Scanner(System.in);
    System.out.println("Enter Student ID:");

    String sID = null;
    if (input.hasNextInt()==false){
        System.out.println("Please re-check the student number inputted. Student number can only be digits.");
        throw new BadUserInputException("Student number can not contain non-digits.");
    }else if (input.next()==""){
        throw new BadUserInputException("Student number can not be empty");
    }

推荐答案

我遇到了这个确切的问题，我相信我已经找到了解决方案.

I am encountering this exact problem, and I believe I figured out a solution.

关键是接受输入作为String类型，并使用.isEmpty()方法检查用户是否输入了任何内容.

The key is to accept input as type String and use the .isEmpty() method to check whether the user entered anything or not.

如果您的字符串被命名为"cheese"，而扫描仪被命名为"in"，则如下所示:

If your String is named "cheese" and your scanner is named "in", here's what this looks like:

cheese = ""; // empty 'cheese' of prior input
cheese = in.nextLine(); //read in a line of input

//if user didn't enter anything (or just spacebar and return)
if(cheese.isEmpty()) {
System.out.println("Nothing was entered. Please try again");
} 
//user entered something
else {
[enter code here checking validity of input]
}

我尝试对整数输入执行此检查，发现最好接受String类型的输入，并使用包装器类将其转换为int类型.如果有

I tried implementing this check for integer input and discovered it's better to accept String type input and convert it to int type with a wrapper class. If you have

int eger = 0; //initialize to zero

然后将这段代码放在上面的else语句中:

then you would put this code in the else statement above:

else{
eger = Integer.valueOf(cheese);
}

我知道这个问题是2年前提出的，但是我发布了这个问题，希望是希望帮助像我这样的人寻找答案. :)

I am aware that this question was asked 2 years ago, but I posted this in hopes of helping others like myself who were looking for an answer. :)

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