Confusion for Java Beginners: Traps and Responses to Array Cross-Borders

Array out-of-bounds refers to accessing elements of the array beyond its boundaries. Causes of this include forgetting the array length, using negative subscripts, and improper loop termination. Countermeasures include: initializing and using boundary variables, using for-each loops, performing boundary checks, using Optional and exception handling in Java 8. By following these best practices, you can prevent array out-of-bounds exceptions and write robust, error-free Java code.

Confusion for Java beginners: Traps and responses to array out-of-bounds

Array out-of-bounds refers to an attempt to access an array beyond its boundaries element. In Java, array subscripts start from 0, which means that an array of size n has only valid subscripts in the range [0, n-1]. Accessing elements outside these ranges will result in an array out-of-bounds exception (IndexOutOfBoundsException).

The reason for array out-of-bounds:

• Forgot the length of the array
• Use negative numbers as subscripts
• Loop failed Correct termination
• The range is not checked when processing user input

Actual case:

The following is an example of an array out of bounds:

int[] arr = {1, 2, 3};

try {
    System.out.println(arr[3]); // 数组越界异常
} catch (IndexOutOfBoundsException e) {
    System.out.println("数组越界");
}

Dealing with the pitfalls of array out-of-bounds:

1. Initialize and use bounded variables:

int[] arr = {1, 2, 3};
int length = arr.length;

2. Use for-each loop:

for (int num : arr) {
    System.out.println(num);
}

3. Use bounds check:

if (index >= 0 && index < arr.length) {
    System.out.println(arr[index]);
} else {
    System.out.println("数组越界");
}

4. Use Optional in Java 8:

Optional<Integer> num = index >= 0 && index < arr.length ? Optional.of(arr[index]) : Optional.empty();
if (num.isPresent()) {
    System.out.println(num.get());
} else {
    System.out.println("数组越界");
}

5. Use exception handling:

try {
    System.out.println(arr[index]);
} catch (IndexOutOfBoundsException e) {
    System.out.println("数组越界");
}

Conclusion:

Array out of bounds is a common mistake among Java beginners. By understanding why an array goes out of bounds and dealing with it through techniques such as bounds checking, using for-each loops, or exception handling, you can effectively prevent such errors. By following these best practices, you can write more robust, error-free Java code.

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