StringIndexOutOfBoundsException in Java - solution to string out of bounds

In Java, StringIndexOutOfBoundsException (string out of bounds) is a common error. This error usually occurs when processing strings, and programs that deal with large amounts of text are likely to be involved in this situation. This article will introduce the situation and solution of StringIndexOutOfBoundsException in Java.

What is StringIndexOutOfBoundsException?

StringIndexOutOfBoundsException is also called String out of bounds. When we use Java string operations, if we access beyond the range of the string, this runtime exception may occur. This exception type inherits from the RuntimeException class.

Common situations

When using the string charAt() method

When we use the charAt() method to obtain the characters of a string, we can specify its Number to get a specific character. If this number exceeds the length of the string, a StringIndexOutOfBoundsException occurs.

For example:

String str = "Java is a good programming language.";
char c = str.charAt(50);

If the characters obtained through the charAt() method exceed the length of the string, an out-of-bounds exception will be thrown.

When using the string substring() method

The substring() method can extract the words in the string, and the length of the substring can be controlled by specifying the starting and ending numbers. If the start and end positions are not within the range of the string, an exception will be thrown.

For example:

String str = "Java is a good programming language.";
String subStr = str.substring(50, 60);

In this case, if the number exceeds the length of the string, an out-of-bounds exception will be thrown.

When using a string array

When using a string array, StringIndexOutOfBoundsException is also prone to occur. If we query for an element that exceeds the length of the array, an exception will be thrown.

For example:

String[] arr = new String[]{"Java", "Python", "C++", "Ruby"};
String str = arr[10];

In the above situation, if the element we refer to is not within the range of the array, an out-of-bounds exception will occur.

Solution

We can avoid StringIndexOutOfBoundsException in the following ways.

When using the charAt() method, make sure that the specified number is within the string range.

String str = "Java is a good programming language.";
if (str.length() > 50) {
    char c = str.charAt(50);
}

When using the substring() method, ensure that the start and end positions are within the range of the string.

String str = "Java is a good programming language.";
if (str.length() > 50 && str.length() > 60) {
    String subStr = str.substring(50, 60);
}

When using a string array, now make sure that the queried element exists in the array.

String[] arr = new String[]{"Java", "Python", "C++", "Ruby"};
if (arr.length > 10) {
    String str = arr[10];
}

Summary

StringIndexOutOfBoundsException is a common exception when processing string operations. We should be careful when using string methods. If an exception occurs, we should check the parameters passed to the string method to ensure that they do not exceed the length of the string.

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