java - System.in.read 导致循环执行三次

Question

import java.io.IOException;
import java.io.InputStreamReader;

public class doSwitch {

    public static void main(String[] args) throws IOException {

        char choice;

        do {
            System.out.println("Welcome User");
            System.out.println("1. Change plan");
            System.out.println("2. Pay Bill");
            System.out.println("3. Complaints");
            System.out.println("4. De-activate account");
            System.out.println("Choose one the above option");


            choice = (char) System.in.read();


        } while (choice < '1' || choice > '4');

        System.out.println("User's Choice:" + choice);

        ///////////////////////////// switch
        ///////////////////////////// case////////////////////////////////////

        switch (choice) {

        case '1':
            System.out.println("There are different plans than you can opt for");
            break;
        case '2':
            System.out.println("Pay bill using credit card or debit card");
            break;
        case '3':
            System.out.println("In case of complaint call 121");
            break;
        case '4':
            System.out.println("Are you sure you want to discontinue with us");
            break;

        }
    }
}

如果我输入 1 到 4 之间的值，此代码可以正常工作。但是如果该值大于 4，则它会执行循环 3 次。我发现它的值是\n，\r。我不明白的是我怎样才能避免它。以及为什么它适用于值 1-4

Answer 1

尝试

 Scanner sc = new Scanner(System.in);

 int choice = sc.nextInt();

System.in.read() 读取单个字节。在您的情况下，它读取实际输入的字符。如果该字符不等于 1-4，则循环继续并读取下一个字节，该字节将作为返回字符。扫描仪对象会为您处理这个问题。