Copying arrays

Learn to copy with System.arraycopy.

Copying arrays

System.arraycopy copies a portion of one array into another. It takes five parameters:

int[] src = {1, 2, 3};
int[] dest = new int[3];
System.arraycopy(src, 0, dest, 0, 3);
// dest = {1, 2, 3}

The parameters are: source array, source start index, destination array, destination start index, number of elements to copy. The destination must be large enough; otherwise an exception is thrown.

arraycopy parameters

System.arraycopy(src, srcPos, dest, destPos, length) — five parameters in order:

src: source array
srcPos: source start index
dest: destination array
destPos: destination start index
length: number of elements to copy

For example, System.arraycopy(src, 1, dest, 0, 2) copies 2 elements starting from src's index 1 into dest's index 0. For partial copies, adjust srcPos and length.

Exercise Copy an array and print

Write a Main class with a main method. Assign {1, 2, 3} to int[] src. Assign new int[3] to int[] dest. Copy with System.arraycopy(src, 0, dest, 0, 3). Print the destination's first element with System.out.println(dest[0]).

Show example solution

public class Main {
    public static void main(String[] args) {
        int[] src = {1, 2, 3};
        int[] dest = new int[3];
        System.arraycopy(src, 0, dest, 0, 3);
        System.out.println(dest[0]);
    }
}

Test yourself

Complete the arraycopy call

System.array____(src, 0, dest, 0, 3);

Show answer

System.arraycopy(src, 0, dest, 0, 3);

Match the arraycopy parameters

src

Source
dest

Destination
srcPos

Source start
length

Element count
System.arraycopy(src, 0, dest, 0, n) — what is n?
- The source array
- Number of elements to copy
- The destination array
- The start index
Show answer

Number of elements to copy — n is the number of elements to copy.

Next lesson: Summary - Arrays

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