Generic method to concatenate two arrays in Java

Write a generic method to concatenate the two array elements. Method signature can be like below.

public static <T> T[] concatArrays(T[] a, T[] b) {
	.......
	.......	
}

 

concatArray method should return

1.   ‘a’ if the array ‘b’ is null or empty

2.   ‘b’ if the array ‘a’ is null or empty

3.   Else return a new array that contain the elements of a followed by the b array elements.

 

Find the below working application.

 

ArraysConcat.java

package com.sample.app.arrays;

import java.lang.reflect.Array;
import java.util.Arrays;

public class ArraysConcat {

	/**
	 * 
	 * @param <T>
	 * @param a
	 * @param b
	 * 
	 * @return 1. Return a if b is null or empty. 2. Return b if a is null or empty.
	 *         3. Return new array that contain the elements of a followed by the b
	 *         array elements
	 */
	public static <T> T[] concatArrays(final T[] a, final T[] b) {

		if (a == null || a.length == 0) {
			return b;
		}

		if (b == null || b.length == 0) {
			return a;
		}

		int aLen = a.length;
		int bLen = b.length;

		@SuppressWarnings("unchecked")
		T[] c = (T[]) Array.newInstance(a.getClass().getComponentType(), aLen + bLen);
		System.arraycopy(a, 0, c, 0, aLen);
		System.arraycopy(b, 0, c, aLen, bLen);

		return c;
	}

	public static void main(String[] args) {
		Integer[] evenNumbers = { 2, 4, 6, 8 };
		Integer[] oddNumbers = { 1, 3, 5, 7 };
		Integer[] emptyArray = {};

		System.out.println(Arrays.toString(concatArrays(evenNumbers, oddNumbers)));
		System.out.println(Arrays.toString(concatArrays(evenNumbers, emptyArray)));
		System.out.println(Arrays.toString(concatArrays(emptyArray, oddNumbers)));

	}

}

Output

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

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