Method System.arraycopy()

The System.arraycopy() method in Java allows you to copy a portion of one array into another quickly and efficiently.

Let's look at an example that copies elements 2, 3, and 4 from the arraySource into the arrayDestination array:

import java.util.Arrays;

public class ArrayCopyExample1 {
    public static void main(String[] args) {
        int[] arraySource = {1, 2, 3, 4, 5, 6};
        int[] arrayDestination = {0, 0, 0, 0, 0, 0, 0, 0};

        System.out.println("arraySource: " + Arrays.toString(arraySource));
        System.out.println("arrayDestination: " + Arrays.toString(arrayDestination));

        System.arraycopy(arraySource, 1, arrayDestination, 2, 3);
        System.out.println("arrayDestination after arrayCopy: " + Arrays.toString(arrayDestination));
    }
}

Output:

arraySource: [1, 2, 3, 4, 5, 6]
arrayDestination: [0, 0, 0, 0, 0, 0, 0, 0]
arrayDestination after arrayCopy: [0, 0, 2, 3, 4, 0, 0, 0]

Note: The syntax of the method is:

System.arraycopy(src, srcPos, dest, destPos, length);

Where:

• src – source array
• srcPos – starting position in the source array
• dest – destination array
• destPos – starting position in the destination array
• length – number of elements to copy

You can also copy elements within the same array, including overlapping regions. This is often useful for array manipulation or shifting values:

import java.util.Arrays;

public class ArrayCopyExample2 {
    public static void main(String[] args) {
        int[] array = {1, 2, 3, 4, 5, 6, 7, 8};
        System.out.println(Arrays.toString(array));

        System.arraycopy(array, 1, array, 3, 3);
        System.out.println(Arrays.toString(array));
    }
}

Output:

[1, 2, 3, 4, 5, 6, 7, 8]
[1, 2, 3, 2, 3, 4, 7, 8]

The System.arraycopy() method performs a shallow copy, meaning that if you copy arrays of objects, only the references are copied, not the actual object contents.

This method is more efficient than manual copying using loops and is widely used in performance-critical applications, such as data buffers and memory manipulation.

Курс 'Java для начинающих' на Udemy