How to Merge Two Arrays in Java: A Simple Guide

Merging two arrays is a common operation in Java, often encountered in various programming tasks. This article explores multiple methods to merge two arrays in Java, catering to different preferences and scenarios.

Method 1: Using Predefined Function

import java.util.Arrays;

public class MergeTwoArrays1 {
    public static void main(String[] args) {
        int[] a = {10, 20, 30, 40};
        int[] b = {50, 60, 70, 80};

        int a1 = a.length;
        int b1 = b.length;
        int c1 = a1 + b1;

        int[] c = new int[c1];

        System.arraycopy(a, 0, c, 0, a1);
        System.arraycopy(b, 0, c, a1, b1);

        System.out.println(Arrays.toString(c));
    }
}

Output:

[10, 20, 30, 40, 50, 60, 70, 80]

Complexity:

• Time Complexity: O(M + N)
• Auxiliary Space: O(M + N)

Here, M is the length of array a, and N is the length of array b.

Method 2: Without Using Predefined Function

public class MergeTwoArrays2 {
    public static void main(String[] args) {
        int a[] = {30, 25, 40};
        int b[] = {45, 50, 55, 60, 65};

        int a1 = a.length;
        int b1 = b.length;
        int c1 = a1 + b1;

        int[] c = new int[c1];

        for (int i = 0; i < a1; i++) {
            c[i] = a[i];
        }

        for (int i = 0; i < b1; i++) {
            c[a1 + i] = b[i];
        }

        for (int i = 0; i < c1; i++) {
            System.out.println(c[i]);
        }
    }
}

Output:

30
25
40
45
50
55
60
65

Complexity:

• Time Complexity: O(M + N)
• Auxiliary Space: O(M + N)

Here, M is the length of array a, and N is the length of array b.

Method 3: Using Java Streams

import java.util.Arrays;
import java.util.stream.IntStream;

public class MergeTwoArraysUsingStreams {
    public static void main(String[] args) {
        int a[] = {30, 25, 40};
        int b[] = {45, 50, 55, 60, 65};

        int[] c = mergeArraysUsingStreams(a, b);

        Arrays.stream(c).forEach(System.out::println);
    }

    public static int[] mergeArraysUsingStreams(int[] arr1, int[] arr2) {
        return IntStream.concat(Arrays.stream(arr1), Arrays.stream(arr2)).toArray();
    }
}

Output:

30
25
40
45
50
55
60
65

Complexity:

• Time Complexity: O(M + N)
• Auxiliary Space: O(M + N)

Here, M is the length of array a, and N is the length of array b.

Method 4: Using ArrayList

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class MergeArrays {
    public static int[] mergeArraysUsingArrayList(int[] a, int[] b) {
        List<Integer> resultList = new ArrayList<>();

        for (int num : a) {
            resultList.add(num);
        }

        for (int num : b) {
            resultList.add(num);
        }

        return resultList.stream()
                .mapToInt(Integer::intValue).toArray();
    }

    public static void main(String[] args) {
        int a[] = {30, 25, 40};
        int b[] = {45, 50, 55, 60, 65};
        int[] result = mergeArraysUsingArrayList(a, b);

        for (int i = 0; i < result.length; i++) {
            System.out.println(result[i]);
        }
    }
}

Output:

30
25
40
45
50
55
60
65

Complexity:

• Time Complexity: O(M + N)
• Auxiliary Space: O(M + N)

Here, M is the length of array a, and N is the length of array b.

These methods offer flexibility in merging arrays, catering to different preferences and requirements. Choose the one that best suits your specific scenario and coding style.