线程“main”中的异常 java.lang.StringIndexOutOfBoundsException：字符串索引超出范围：5

Question

What is wrong with my code (Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 5)........

public class AAExample {
    public static void main(String[] args) {
        AAExample nn = new AAExample();
        System.out.println(nn.isXOrZ("Pony"));
    }

    public  boolean isXOrZ(String text) {
    String  lower = text.toLowerCase();
    boolean found = false;
    int     i     = 0;

    while (!found) {
        String letter = lower.substring(i, i +1);

            if(letter.equals("z") || letter.equals("x"))
            found = true;

            i++;
        }

        return found;
    }
}

Answer 1

Your while loop keep looping until x or z is found. Infinite loop occur when there is actually no x or z in your String .

StringIndexOutOfBoundsException occur when i >= lower.length()-1

So you need to modify your while loop to

 while (!found && i < lower.length()-1)

Answer 2

Your loop terminating condition only relies on whether character is found or not.

while (!found)

Suppose, you don't found anything then you will never do

if(letter.equals("z") || letter.equals("x"))
   found=true

and keep on incrementing i , which will give you StringIndexOutOfBoundsException once it will be equals to string's length

Answer 3

You are looping through the string until x or z is found. If x or z is not found, the loop will continue on past the end of the string. This causes the exception.

I would recommend a for loop:

for(int i = 0; i < lower.length; i++) {
    String letter = lower.substring(i, i + 1);
    if(letter.equals("x") || letter.equals("z")) return true;
} 
return false;