Tips and things to note when adding elements to an array in Java

Tips and precautions for adding elements to arrays in Java

In Java, arrays are a very common and important data structure. It can store a set of elements of the same type, and these elements can be accessed and modified through indexes. In practical applications, we often need to dynamically add elements to an array. This article will introduce some tips and precautions for adding elements to arrays in Java, and provide corresponding code examples.

1. Use dynamic array (ArrayList) to add elements

Dynamic array ArrayList is a dynamically growing array provided by Java. By using ArrayList, we can easily add and remove elements to the array. The specific usage is as follows:

import java.util.ArrayList;

public class ArrayAddExample {
    public static void main(String[] args) {
        // 创建一个动态数组
        ArrayList<Integer> numbers = new ArrayList<>();

        // 向数组中添加元素
        numbers.add(10);
        numbers.add(20);
        numbers.add(30);

        // 打印数组元素
        System.out.println("数组元素：");
        for (int i = 0; i < numbers.size(); i++) {
            System.out.println(numbers.get(i));
        }
    }
}

By calling the numbers.add() method, elements can be added to the dynamic array. Using the numbers.get() method, you can get elements in the array based on index. Note that the length of dynamic arrays can be automatically adjusted as needed.

2. Use a static array to insert elements at a specified position

In a static array, we cannot add elements directly because the length of the static array is determined when it is created. However, we can insert elements at the specified position through the following steps:

• Create a new array with a length 1 larger than the original array
• Copy the elements in the original array to into the new array and insert a new element at the specified position
• Assign the new array to the original array variable

The following is a sample code that demonstrates the process of inserting elements into a static array :

public class ArrayInsertExample {
    public static void main(String[] args) {
        int[] numbers = {10, 20, 30, 40, 50};
        int insertIndex = 2;
        int insertValue = 25;

        // 创建新数组
        int[] newNumbers = new int[numbers.length + 1];

        // 复制原数组元素到新数组，并在指定位置插入新元素
        for (int i = 0, j = 0; i < newNumbers.length; i++, j++) {
            if (i == insertIndex) {
                newNumbers[i] = insertValue;
                j--;
            } else {
                newNumbers[i] = numbers[j];
            }
        }

        // 将新数组赋值给原数组
        numbers = newNumbers;

        // 打印数组元素
        System.out.println("数组元素：");
        for (int i = 0; i < numbers.length; i++) {
            System.out.println(numbers[i]);
        }
    }
}

In the above code, we create a new array newNumbers with a length of numbers.length 1. Then, copy the elements in the original array numbers to the new array through a loop, and insert the new element insertValue at the specified position insertIndex. Finally, assign the new array to the original array numbers.

It should be noted that if the position to be inserted exceeds the range of the original array, or is a negative number, the element cannot be inserted.

3. Bounds checking when adding elements

When adding elements to an array, we need to perform bounds checking to ensure that the range of the array is not exceeded. Otherwise, an ArrayIndexOutOfBoundsException exception may be thrown.

For example, for a static array, when adding elements using an index, you can perform boundary checking by determining whether the index is greater than or equal to 0 and less than the array length. For dynamic arrays ArrayList, no bounds checking is required because the length is automatically adjusted.

int index = 5;
if (index >= 0 && index < numbers.length) {
    numbers[index] = 55;
} else {
    System.out.println("非法索引！");
}

In the above code, we first determine whether index is within the legal range. If so, the element can be safely assigned to the array; otherwise, an error message is output.

In actual development, in order to avoid bounds checking and exception handling, we can use dynamic array ArrayList. It can automatically adjust the length without any cross-border problems.

Summary:

In Java, we can use dynamic array ArrayList or insert elements by copying the original array to dynamically add elements to the array. Using a dynamic array ArrayList is more convenient and safer because it automatically adjusts the length. If you want to use a static array, you need to perform bounds checking when inserting elements at specified positions. It should be noted that when inserting elements, you should ensure that the range of the array is not exceeded.

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