Java Array Concatenation

Concatenating Arrays in Java (for Spring Boot & beyond)

Java doesn't directly support array concatenation. Use System.arraycopy() for primitive types or Arrays.copyOf() and System.arraycopy() for a more efficient approach with larger arrays. For objects, Arrays.stream() offers concise solutions.

Method 1: System.arraycopy() (Primitive Types)

int[] arr1 = {1, 2, 3};
int[] arr2 = {4, 5, 6};
int[] result = new int[arr1.length + arr2.length];
System.arraycopy(arr1, 0, result, 0, arr1.length);
System.arraycopy(arr2, 0, result, arr1.length, arr2.length);
//result: [1, 2, 3, 4, 5, 6]

Method 2: Arrays.copyOf() and System.arraycopy() (Efficient for large arrays)

int[] arr1 = {1,2,3};
int[] arr2 = {4,5,6,7,8,9,10};
int[] result = Arrays.copyOf(arr1, arr1.length + arr2.length);
System.arraycopy(arr2, 0, result, arr1.length, arr2.length);
//result: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Method 3: Arrays.stream() (Objects)

String[] arr1 = {"a", "b"};
String[] arr2 = {"c", "d"};
String[] result = Stream.concat(Arrays.stream(arr1), Arrays.stream(arr2))
                        .toArray(String[]::new);
//result: [a, b, c, d]

Method 4: ArrayList (Flexible & efficient for frequent modifications)

For dynamic array manipulation, consider ArrayList:

List<Integer> list1 = Arrays.asList(1,2,3);
List<Integer> list2 = Arrays.asList(4,5,6);
List<Integer> result = new ArrayList<>(list1);
result.addAll(list2);
//result: [1, 2, 3, 4, 5, 6]

Choose the method best suited to your data type and performance requirements. For Spring Boot, these methods are directly applicable within your services and controllers. Remember to handle potential NullPointerExceptions if arrays might be null.