How to solve Java string index out of range exception (StringIndexOutOfBoundsException)

How to solve the Java string index out-of-range exception (StringIndexOutOfBoundsException)

Introduction: In Java programming, the StringIndexOutOfBoundsException exception is a frequently encountered exception. This exception is mainly caused by the index of the string exceeding the length range of the string. This article discusses how to resolve this exception and provides corresponding code examples.

1. Cause of exception
In Java, a string is a character sequence composed of characters. String indexing starts from 0. When we use an index to access characters in a string, if the index exceeds the length range of the string, a StringIndexOutOfBoundsException exception will occur.

2. Solution
In order to solve the Java string index out-of-range exception, we can take the following methods:

1. Check the length of the string before using the index
   Before using the index, we can check the length of the string to ensure that the index does not exceed the range of the string. You can use the length() method of the String class to get the length of the string, and then compare it with the index.

String str = "Hello World";
int index = 10;
if (index >= 0 && index < str.length()) {
    char ch = str.charAt(index);
    System.out.println(ch);
} else {
    System.out.println("索引超出范围");
}

2. Use try-catch block to catch exceptions
   Another solution is to use try-catch block to catch StringIndexOutOfBoundsException exception and handle it accordingly in the exception handling block.

String str = "Hello World";
int index = 10;
try {
    char ch = str.charAt(index);
    System.out.println(ch);
} catch(StringIndexOutOfBoundsException e) {
    System.out.println("索引超出范围");
}

3. Practical Example
Below we use a practical example to understand and apply the above solutions in more detail.

public class StringIndexOutOfBoundsExceptionExample {
    public static void main(String[] args) {
        String str = "Java is a great programming language";
        int index = 50;
        
        // 方案一：使用索引之前先检查字符串的长度
        if (index >= 0 && index < str.length()) {
            char ch = str.charAt(index);
            System.out.println(ch);
        } else {
            System.out.println("索引超出范围");
        }
        
        // 方案二：使用try-catch块捕获异常
        try {
            char ch = str.charAt(index);
            System.out.println(ch);
        } catch(StringIndexOutOfBoundsException e) {
            System.out.println("索引超出范围");
        }
    }
}

In the above code example, we first define a string "Java is a great programming language", and then set an index of 50 that exceeds the length range of the string.

Using option one, we first check whether the index is within a reasonable range. If so, obtain the corresponding character through the charAt() method and print the output. If the index is out of range, the prompt message "Index out of range" is output.

Using option 2, we use the try-catch block to catch the StringIndexOutOfBoundsException exception. In the try block, we use the charAt() method to get the corresponding character and print the output. If the index is out of range, a StringIndexOutOfBoundsException will be thrown. In the catch block, we catch the exception and output the prompt message "Index out of range".

By running the above code example, we can get the following output:

索引超出范围
索引超出范围

So far, we have learned how to solve the Java string index out of range exception (StringIndexOutOfBoundsException). By checking the string length and catching the exception using a try-catch block, we can effectively resolve this exception and ensure the normal execution of the program. I hope this article is helpful to you, thank you for reading!

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