java - 为什么在 while 循环中行会重复出现？

Question

我制作了一个简单的程序，可以选择添加、投票和查看对 3 个不同候选人的投票。由于某种原因，第 18 行及其后面的第 72 行重复出现，例如，如果您开始按 1 创建候选者，输入名称并按 Enter 键，它将如下所示:

Add candidate (1) or vote (2) or view number of votes on each candidate (3): Incorrect number, please try again.

但随后又恢复正常...

Add candidate (1) or vote (2) or view number of votes on each candidate (3):

这是完整的代码(重复的行已注明):

package array;

import java.util.Scanner;

public class Array {

    public static void main(String[] args) {
        char[] Vote_Choice = {'A', 'B', 'C'};
        String[] candidates = { "none", "none", "none"};
        int[] votes = {0, 0, 0};


        Scanner input = new Scanner(System.in);
        boolean done = false;

        while (!done) {
            boolean done2 = false;
                System.out.print("Add candidate (1) or vote (2) or view number of votes on each candidate (3): ");   // here (line 18)

            switch (input.nextLine()) {
                case "1": System.out.print("Type new candidates name: ");
                    while (!done2) {
                        if (candidates[0].equals("none")) {
                        candidates[0] = input.next();
                        done2 = true;
                    }
                        else if (!candidates[0].equals("none") && candidates[1].equals("none")) {
                        candidates[1] = input.next();
                        done2 = true;

                    }
                    else if (!candidates[0].equals("none") && !candidates[1].equals("none") && candidates[2].equals("none")) {
                        candidates[2] = input.next();
                        done2 = true;
                    }
                    else if (!candidates[0].equals("none") && !candidates[1].equals("none") && !candidates[2].equals("none")) {
                        System.out.println("Sorry, all candidate slots are full.");
                        done2 = true;
                    }
                    }
                        break;
                case "2":
                    System.out.println("Type letter corresponding to the candidate you wish to vote for: ");

                    System.out.print("Type A for candidate "+ candidates[0] +", type B for candidate "+candidates[1]+", type C for candidate "+candidates[2]+": ");
                    String choice = input.next();
                    if (choice.equals("A")) {
                        votes[0]++;
                    }
                    if (choice.equals("B")) {
                        votes[1]++;
                    }
                    if (choice.equals("C")) {
                        votes[2]++;
                    }


                    break;
                case "3": if (!candidates[0].equals("none")) {
                    System.out.println("Candidate "+ candidates[0] +": "+votes[0]);
                } 
                            if (!candidates[1].equals("none")) {
                    System.out.println("Candidate "+ candidates[1] +": "+votes[1]);
                } 
                            if (!candidates[2].equals("none")) {
                    System.out.println("Candidate "+ candidates[2] +": "+votes[2]);
                } 
                            else {
                                System.out.println("Sorry, there are no current candidates.");
                            }
                break;
                default: System.out.println("Incorrect number, please try again.");  // And here, line 72
            }       

        }


    }
}

Answer 1

这是因为您有 input.next() 而不是 input.nextLine() 。行尾“保留”在输入流中，当您调用它时，它返回该流中剩下的内容(通常是空字符串)。