防止 Java 中 List.subList() 引发 IndexOutOfBoundsException_AI阅读总结 — 包阅AI

The List.subList() method in Java allows you to create a view of a portion of a list, defined by a starting and ending index. However, improper use of this method can lead to IndexOutOfBoundsException. This article will explore how subList() works and how to avoid this exception through proper usage.

1. Overview of List.subList()

The subList(int fromIndex, int toIndex) method returns a view of the portion of this list between the specified fromIndex, inclusive, and toIndex, exclusive. The returned list is backed by the original list, meaning that changes to the sublist will be reflected in the original list, and vice-versa.

1.1 Common Causes of IndexOutOfBoundsException

The IndexOutOfBoundsException occurs when:

• The fromIndex is less than 0.
• The toIndex is greater than the size of the list.
• The fromIndex is greater than the toIndex.

2. Demonstrating the Exception with Examples

Here’s an example demonstrating various scenarios that can lead to IndexOutOfBoundsException:

SubListExample.java

public class SubListExample {    public static void main(String[] args) {        List<String> originalList = new ArrayList<>(Arrays.asList("A", "B", "C", "D", "E"));        // Case 1: fromIndex < 0        List<String< sublist = originalList.subList(-1, 3);        System.out.println(sublist);        // Case 2: toIndex > size        List<String> sublist2 = originalList.subList(2, 6);        System.out.println(sublist2);        // Case 3: fromIndex > toIndex        List<String> sublist3 = originalList.subList(4, 2);        System.out.println(sublist3);    }}

The code above (Case 1) produces the following output:

2.1 Reason for Failure

• Case 1: fromIndex < 0: The fromIndex parameter is less than 0. subList(int fromIndex, int toIndex) requires fromIndex to be non-negative. Negative indices are invalid, thus an IndexOutOfBoundsException is thrown.
• Case 2: toIndex > size: The toIndex parameter exceeds the size of the list. subList(int fromIndex, int toIndex) requires toIndex to be less than or equal to the size of the list. In this example, the list has a size of 5, so the maximum valid toIndex is 5. Since toIndex is 6, an IndexOutOfBoundsException is thrown.
• Case 3: fromIndex > toIndex: The fromIndex parameter is greater than the toIndex parameter. subList(int fromIndex, int toIndex) requires fromIndex to be less than or equal to toIndex. Since fromIndex is 4 and toIndex is 2, an IllegalArgumentException (a subtype of IndexOutOfBoundsException) is thrown.

3. Avoiding the Exception

To avoid IndexOutOfBoundsException, always ensure that:

• fromIndex is greater than or equal to 0.
• toIndex is less than or equal to the size of the list.
• fromIndex is less than or equal to toIndex.

Here is how we can safely use subList():

SafeSubListExample.java

public class SafeSubListExample {    public static void main(String[] args) {        List<String> originalList = new ArrayList<>(Arrays.asList("A", "B", "C", "D", "E"));        int fromIndex = 1;        int toIndex = 4;        if (fromIndex >= 0 && toIndex <= originalList.size() && fromIndex <= toIndex) {            List<String> sublist = originalList.subList(fromIndex, toIndex);            System.out.println("Sublist: " + sublist);        }    }}

The provided code snippet above demonstrates the safe and correct usage of the subList() method to avoid IndexOutOfBoundsException by validating the indices before calling the method. By checking that fromIndex is non-negative, toIndex does not exceed the list size, and fromIndex is less than or equal to toIndex, the code safely creates a sublist of the original list.

4. Conclusion

In this article, we explored how to effectively use the subList() method in Java lists while avoiding the common IndexOutOfBoundsException. We discussed how subList() works, provided examples of scenarios that cause the exception. By understanding the constraints and correctly using indices, we can utilize the power of subList() without encountering errors. In conclusion, ensuring that indices are within valid bounds is key to preventing IndexOutOfBoundsException.

5. Download the Source Code

This article covers Java’s List.subList() method and how to prevent IndexOutOfBoundsException.