在扫描程序验证中将回车键视为无效

Question

我有这个代码...

import java.util.*;
public class SwitchExample {
    public static void main(String[] args) {
        System.out.print("Enter ID: ");
        Scanner scanner = new Scanner(System.in);
        while (!scanner.hasNextInt()) {
            System.out.print("Invalid. Enter again: ");
            scanner.next();
        }
        int number = scanner.nextInt();
        System.out.println("Your number was: " + number);
        System.out.println("Test message got printed!");
    }
}

键入

有效的输入是可以的，并且在键入无效字符后，它仍然可以按要求工作。但是，键入回车键时，无论哪种情况都不会引发错误。请帮助我如何实现这一目标。我尝试了多种方法，但没有一种奏效。

Answer 1

好吧，您只是在扫描整数尝试扫描"下一行"

while(scanner.hasNextLine()) 

如果你按回车键，那会抓住，我假设是这样。

Answer 2

对于 enter，您需要添加一个特殊情况，如下所示

String line = scanner.nextLine();
if (line .isEmpty()) {
        System.out.println("Enter Key pressed");
}

以下是满足您需求的完整源代码：

public static void main(String[] args) {
    System.out.print("Enter ID: ");
    Scanner scanner = new Scanner(System.in);
    String readString = scanner.nextLine();
    while(readString!=null) {
        System.out.println(readString);
        if (readString.isEmpty()) {
            System.out.println("Read Enter Key.");
        }
        else if (isInteger(readString)) {
            System.out.println("Read integer");
        }
        else{
            System.out.println("Read char");
        }
        if (scanner.hasNextLine()) {
            readString = scanner.nextLine();
        } else {
            readString = null;
        }
    }
}
public static boolean isInteger(String s) {
    Scanner sc = new Scanner(s.trim());
    if(!sc.hasNextInt()) return false;
    // we know it starts with a valid int, now make sure
    // there's nothing left!
    sc.nextInt();
    return !sc.hasNext();
}