不能一起使用Scanner.nextInt()和Scanner.nextLine()

Question

我必须得到一个字符串输入和一个整数输入,但是输入顺序应该是整数首先出现然后应该要求用户输入字符串

Scanner in = new Scanner(System.in);


    input = in.nextLine();
    k = in.nextInt();

    in.close();

上面的代码工作正常,但如果我首先采用整数输入,如下面的代码

Scanner in = new Scanner(System.in);

    k = in.nextInt();
    input = in.nextLine();


    in.close();

然后它抛出java.lang.ArrayIndexOutOfBoundsException.

这是我的源文件的完整代码:

import java.util.Scanner;

public class StringSwap {

public static void main(String args[]) {
    String input;
    int k;

    Scanner in = new Scanner(System.in);

    k = in.nextInt();
    input = in.nextLine();


    in.close();

    int noOfCh = noOfSwapCharacters(input);
    originalString(input, noOfCh, k);

}

public static int noOfSwapCharacters(String s) {

    char cS[] = s.toCharArray();
    int i = 0, postCounter = 0;
    while (cS[i] != '\0') {
        if (cS[i] != '\0' && cS[i + 1] != '\0') {

            cS[cS.length - 1 - postCounter] = '\0';

            postCounter++;

        }
        i++;
    }

    return postCounter;

}

public static void originalString(String s, int noOfCh, int k) {    
    int counter = 1, chCounter = 0;
    char cArray[] = s.toCharArray();
    String post = "";
    String pre = "";
    String finalString = "";
    char temp;

    for (int i = 1; i <= k; i++) {
        chCounter = 0;
        counter = 1;
        post = "";
        pre = "";

        for (int j = 0; j < cArray.length; j++) {

            if (counter % 2 == 0 && chCounter <= noOfCh) {
                temp = cArray[j];
                post = temp + post;
                cArray[j] = '\0';
                chCounter++;

            }
            counter++;

        }
        for (int h = 0; h < cArray.length; h++) {

            if (cArray[h] != '\0')
                pre = pre + cArray[h];

        }

        finalString = pre + post;
        for (int l = 0; l < finalString.length(); l++) {
            cArray[l] = finalString.charAt(l);

        }

    }

    System.out.println(finalString);
}

}

请指出我在这里做错了什么.

Answer 1

问题是'\n'整数后面的字符.当你打电话时nextInt,扫描仪会读取int,但它不会消耗'\n'它后面的字符; nextLine那样做.这就是为什么你得到一个空行而不是你期望得到的字符串.

假设您的输入具有以下数据:

12345
hello

以下是输入缓冲区最初的外观(^表示Scanner读取下一条数据的位置):

1  2  3  4  5 \n h  e  l  l  o \n
^

之后nextInt,缓冲区看起来像这样:

1  2  3  4  5 \n h  e  l  l  o \n
              ^

第一个nextLine消耗\n,留下你的缓冲区如下:

1  2  3  4  5 \n h  e  l  l  o \n
                 ^

现在nextLine调用将产生预期的结果.因此,要修复程序,您只需要在nextLineafter之后添加另一个调用nextInt,并丢弃其结果:

k = in.nextInt();
in.nextLine(); // Discard '\n'
input = in.nextLine();