如何使用Scanner处理由无效输入(InputMismatchException)引起的无限循环

所以,我对这段代码感到困惑：

import java.util.InputMismatchException;
import java.util.Scanner;

public class ConsoleReader {

    Scanner reader;

    public ConsoleReader() {
        reader = new Scanner(System.in);
        //reader.useDelimiter(System.getProperty("line.separator"));
    }

    public int readInt(String msg) {
        int num = 0;
        boolean loop = true;

        while (loop) {
            try {
                System.out.println(msg);
                num = reader.nextInt();

                loop = false;
            } catch (InputMismatchException e) {
                System.out.println("Invalid value!");
            } 
        }
        return num;
    }
}

这是我的输出：

Insert a integer number:
Invalid value!
Insert a integer number:
Invalid value!
…

解决方法:

根据扫描仪的javadoc：

When a scanner throws an
InputMismatchException, the scanner
will not pass the token that caused
the exception, so that it may be
retrieved or skipped via some other
method.

这意味着如果下一个标记不是int,它会抛出InputMismatchException,但令牌仍然存在.因此,在循环的下一次迭代中,reader.nextInt()再次读取相同的标记并再次抛出异常.你需要的是用它.在catch中添加reader.next()以使用令牌,该令牌无效且需要被丢弃.

...
} catch (InputMismatchException e) {
    System.out.println("Invalid value!");
    reader.next(); // this consumes the invalid token
} 

标签：java-util-scanner,java,infinite-loop
来源： https://codeday.me/bug/20190911/1802739.html