我从Eclipse得到了奇怪的错误

Question

import java.util.Scanner;
public class UserInput {

  public static void main(String[] args) {
    // TODO Auto-generated method stub

        boolean alpha = false;
        boolean numeric = false;
        boolean accepted = true;
        boolean underscore=false;

        Scanner s = new Scanner(System.in);
        System.out.println("please Enter an Idintifire: " +s);
            char c = s.next().trim().charAt(0);
            if (Character.isDigit(c))
            {
              numeric = true;

            } else if (Character.isLetter(c))
            {
                alpha = true;

            } 
            else if (Character.isUnicodeIdentifierPart(c))
            {
              underscore = true;
            }
            else
            {
                accepted = false;

            }

        if (accepted && alpha && numeric && underscore)
        {
            System.out.println("this is an idintifire " +c);
        }

        else {
          System.out.println(c+ " this not an idintifire ");

        }
        s.close();
       }
    }     

输出：

please Enter an Idintifire: java.util.Scanner[delimiters=\p{javaWhitespace}+][position=0][match valid=false][need input=false][source closed=false][skipped=false][group separator=\,][decimal separator=\.][positive prefix=][negative prefix=\Q-\E][positive suffix=][negative suffix=][NaN string=\Q?\E][infinity string=\Q?\E]

我希望用户只输入一个字母数字字;例如，（ab_23）不是（ab 23）

有什么建议吗？

Answer 1

 Scanner s = new Scanner(System.in);
 System.out.println("please Enter an Idintifire: " +s);

您正在上面的行中打印您创建的扫描仪对象的值。尝试删除print语句中的s。

        System.out.println("please Enter an Idintifire: ");

修改

Scanner s = new Scanner(System.in);
System.out.println("please Enter an Idintifire: ");
String input = s.next();
for(int i=0;i< s.length();i++){
char c = input.charAt(i);
        if (Character.isDigit(c))
        {
          numeric = true;

        } else if (Character.isLetter(c))
        {
            alpha = true;

        } 
        else if (Character.isUnicodeIdentifierPart(c))
        {
          underscore = true;
        }
        else
        {
            accepted = false;

        }

  }

   if (accepted && alpha && numeric && underscore)
    {
        System.out.println("this is an idintifire " +input);
    }

    else {
      System.out.println(input+ " this not an idintifire ");

    }