在Java中将子字符串与字符串进行比较 [英] Comparing a Substring to a string in Java

问题描述

所以基本上，用户输入2个字符串（CATSATONTHEMAT AT），我们需要计算第二个字符串在第一个字符串中出现的次数（所以这里的答案是3）

so basically, a user inputs 2 strings ( CATSATONTHEMAT AT ) and we need to count how many time the second string appears in the first string ( so the answer here is 3 )

这是我到目前为止，它一直在说

this is what I have so far, and it keeps saying

线程中的异常mainjava.lang.StringIndexOutOfBoundsException：String index超出范围： 81223
at java.lang.String.substring（Unknown Source）
at practice.main（practice.java:60）

"Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 81223 at java.lang.String.substring(Unknown Source) at practice.main(practice.java:60)"

任何帮助将不胜感激！我只是看不到找到我错了的地方。

any help would be appreciated! I just can't see to find where I went wrong

    String s = scan.next(); // CATSATONTHEMAT
    String t = scan.next(); // AT

    int j= 0;

    for ( int i = 0 ; i < s.length(); i++){
        int k = t.length();
        String newstring = s.substring(i,i+k); // I printed this and the substring works so the if statement might not be working..

        if(newstring.equals(t))
            j++;   // if the new substring equal "AT" then add 1
        }

    System.out.printf("%d", j);  // suppose to print just 3

推荐答案

outOfBounds异常当我接近s的结束和k接受你通过字符串的结尾。

The outOfBounds exception happens when i is near the end of s and k takes you passed the end of the string.

你需要改变循环只到达s.length -t.length（）

You need to change the loop to only go up to s.length()-t.length()

for ( int i = 0 ; i < s.length()-t.length(); i++){

我也建议将int k = t.length for循环。您不需要指定每次迭代，因为每次迭代都应该是相同的。

I would also recommend bringing the int k = t.length() out of the for loop. You don't need to assign that every iteration as it should be the same for every iteration.

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