Combine arrays. Two arrays exist. We can combine them into a third array. We can do this in different ways. Some are more efficient, and others have simpler syntax.
By creating another array, we can copy all elements into a single region of storage. For-loops can be used to quickly copy these elements.
For-loop example. Let us begin with this example. We have two arrays—they can have any number of elements, but in this example they both have 6 elements.
Info We create a new array called "merged." This must have the total number of elements required.
Then In the first for-loop we copy the first elements into the merged array. The second for-loop must use an offset.
Tip The offset for the second for-loop ensures we do not overwrite the elements from the first array.
import java.util.Arrays;
public class Program {
public static void main(String[] args) {
int[] array1 = { 1, 2, 3, 4, 5 };
int[] array2 = { 5, 4, 3, 2, 1 };
// Create empty array of required length.int[] merged = new int[array1.length + array2.length];
// Copy first array into new array.for (int i = 0; i < array1.length; i++) {
merged[i] = array1[i];
}
// Copy second array into new array.// ... Use offset to assign elements.for (int i = 0; i < array2.length; i++) {
merged[array1.length + i] = array2[i];
}
// Print results.
System.out.println(Arrays.toString(array1));
System.out.println(Arrays.toString(array2));
System.out.println(Arrays.toString(merged));
}
}[1, 2, 3, 4, 5]
[5, 4, 3, 2, 1]
[1, 2, 3, 4, 5, 5, 4, 3, 2, 1]
Collections.addAll. This approach is a little simpler. We create an ArrayList of the required element type. Then we use Collections.addAll to add both arrays to it.
Finally We can convert our ArrayList back into a single array with the toArray method.
Note We must pass an array reference to the toArray method. This is where our new array will be placed.
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
public class Program {
public static void main(String[] args) {
// Two string arrays we want to combine.
String[] array1 = { "cat", "bird", "fish" };
String[] array2 = { "ant", "bee" };
System.out.println(Arrays.toString(array1));
System.out.println(Arrays.toString(array2));
// Create an ArrayList.// ... Add all string arrays with addAll.ArrayList<String> list = new ArrayList<>();
Collections.addAll(list, array1);
Collections.addAll(list, array2);
// Display ArrayList contents.
System.out.println(list.toString());
// Convert ArrayList to String array.// ... This is the final merged array.String[] merged = new String[list.size()];
list.toArray(merged);
System.out.println(Arrays.toString(merged));
}
}[cat, bird, fish]
[ant, bee]
[cat, bird, fish, ant, bee]
[cat, bird, fish, ant, bee]
Notes, Collections.addAll. With Collections.addAll, we cannot add int arrays to an ArrayList of Integers. For int arrays, using for-loops is a better solution.
With for-loops or an ArrayList and Collections.addAll we can combine arrays. For more than two arrays, Collections.addAll may be simpler—fewer offsets will be needed.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.