尝试运行代码时出现异常。字符串索引超出范围

提问者：小点点

尝试运行代码时出现异常。字符串索引超出范围

每当我尝试运行代码时，在我输入我想购买多少张彩票后，它都会给我一个错误。这是用于彩票程序的。这是代码

import java.util.Scanner;
public class Lottery {
public static void main(String[] args) {
    //local data
    String guess;
    int numTickets;
    int counter;
    Scanner in = new Scanner(System.in);

    //output
    System.out.println("How many tickets would you like to buy?");
    numTickets = in.nextInt();
    for (counter = 0; counter < numTickets; counter++) {
        System.out.println("Please enter your three numbers (e.g. 123): ");
        guess = in.nextLine();
        int randNum = (int) (Math.random() * 1000);
        String randNumb;
        randNumb = Integer.toString(randNum);
        char ch1 = randNumb.charAt(0);
        char ch2 = randNumb.charAt(1);
        char ch3 = randNumb.charAt(2);

        if (ch1 == guess.charAt(0) && ch2 == guess.charAt(1) && ch3 == guess.charAt(2)) {
            System.out.print("Winner: " + randNumb);
            System.out.print("Congratulations, both pairs matched. /n");
        } else if (ch3 == guess.charAt(2) && ch2 == guess.charAt(1)) {
            System.out.print("Winner: " + randNumb);
            System.out.print("Congratulations, the end pair matched.");
        } else if (ch1 == guess.charAt(0) && ch2 == guess.charAt(1)) {
            System.out.print("Winner: " + randNumb);
            System.out.print("Congratulations, the first pair matched.");
        } else {
            System.out.print("The Correct Number: " + randNumb);
        }
        System.out.println("\t Sorry, no matches,  You only had");
        System.out.println("\t one chance out of 100 to win anyway.");

       }
    }
}

例外情况：

线程中的异常\"main"java.lang.StringIndexOutOfBoundsException：字符串索引超出范围：0 atjava.lang.String.charat（String.java:658）atlottery.Lottery.main（Lottery.java:32）C：\用户\Ben\AppData\本地\NetBeans\缓存\8.1\执行器片段\run.xml:53：Java返回：1

这是我尝试运行程序时显示的异常错误。帮助将不胜感激！

共1个答案

匿名用户

该错误是由< code>Scanner的< code>nextInt方法的行为引起的。此外，您的代码还有其他错误。

< code>nextInt方法只读取下一个整数，不读取其他任何内容。这意味着不读取新行字符(取决于操作系统，\n或\r或\r\n)。这很好，直到您调用< code>nextLine。< code>nextLine读取每个字符，直到遇到新的行字符。因此< code>nextLine看到这个未读的新行字符，并停止进一步读取，它返回一个空字符串，然后将这个空字符串放入< code>guess变量中。当您尝试使用< code>charAt(0)访问< code>guess的第一个字符时，它会崩溃，因为< code>guess没有任何字符。

我建议您使用< code > integer . parse int(in . nextline())从用户处读取一个整数。

我已经为您修复了代码：

String guess;
int numTickets;
int counter;
Scanner in = new Scanner(System.in);

//output
System.out.println("How many tickets would you like to buy?");
numTickets = Integer.parseInt(in.nextLine());
Random rand = new Random();
for (counter = 0; counter < numTickets; counter++) {
    System.out.println("Please enter your three numbers (e.g. 123): ");
    guess = in.nextLine();
    int randNum = rand.nextInt(1000); 
    String randNumb = String.format("%03d", randNum);
    char ch1 = randNumb.charAt(0);
    char ch2 = randNumb.charAt(1);
    char ch3 = randNumb.charAt(2);

    if (ch1 == guess.charAt(0) && ch2 == guess.charAt(1) && ch3 == guess.charAt(2)) {
        System.out.print("Winner: " + randNumb);
        System.out.print("Congratulations, both pairs matched. /n");
    } else if (ch3 == guess.charAt(2) && ch2 == guess.charAt(1)) {
        System.out.print("Winner: " + randNumb);
        System.out.print("Congratulations, the end pair matched.");
    } else if (ch1 == guess.charAt(0) && ch2 == guess.charAt(1)) {
        System.out.print("Winner: " + randNumb);
        System.out.print("Congratulations, the first pair matched.");
    } else {
        System.out.print("The Correct Number: " + randNumb);
    }
    System.out.println("\t Sorry, no matches,  You only had");
    System.out.println("\t one chance out of 100 to win anyway.");

}

如您所见，我进行了其他改进。首先，Math.random（） * 1000 可以返回非三位数字，所以我更改了它，使其使用 Random 对象。使用 rand.nextInt（900） 100 只能生成三位数字。

其次，正如XtremeBaumer在评论中所说，我使用了< code > string . value of(rand num)。