Combine two integer arrays into one array in java

Question

I've seen similar questions and none provide the answer that I'm looking for, so I apologize in advance if this is considered a duplicate. I'm trying to combine arrays {1, 2, 3} and {4, 5, 6} into {1, 2, 3, 4, 5, 6}. What am I doing incorrectly? I'm super new to java. Sorry if the question is stupid.

public class combine {
  public static void main(String[]args){

  int[]a = {1, 2, 3};
  int[]b = {4, 5, 6};
  int[]c = new int[a+b];
  for(int i=0; i<a.length; i++)
  System.out.print(c[i]+" ");
}
public static int[]merge(int[]a, int[]b){
  int[]c = new int[a.length+b.length];
  int i;
  for(i=0; i<a.length; i++)
     c[i] = a[i];

     for(int j=0; j<b.length; j++)
        c[i++]=b[j];
        return c;
}
}

in some place call `merge`, and actually is not a merge is like `concatenate` :P — nachokk, Dec 01 '13 at 19:59
It's also defined locally in the method; it would never print the correct array. — Jeroen Vannevel, Dec 01 '13 at 20:00
possible duplicate of [How to concatenate two arrays in Java?](http://stackoverflow.com/questions/80476/how-to-concatenate-two-arrays-in-java) — Abimaran Kugathasan, Mar 20 '14 at 05:18

score 9 · Answer 1 · answered Dec 01 '13 at 20:07

9

Don't do it yourself, use System.arrayCopy() to copy both arrays into a new array of the combined size. That's much more efficient, as it uses native OS code.

answered Dec 01 '13 at 20:07

Sean Patrick Floyd

292,901
67
465
588

is it because of deep copying vs shallow copying? – Kick Buttowski Oct 25 '18 at 03:35
1

No, both versions are shallow, but System.arrayCopy() uses OS routines instead of Java abstractions. – Sean Patrick Floyd Oct 25 '18 at 17:21

Alexis C. · Accepted Answer · 2013-12-01T20:04:26.327

6

Instead of

int[]c = new int[a+b];

You need to call your merge method and assign the result to the array like :

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

Also you for loop should be :

int[]c = merge(a,b);
for(int i=0; i<c.length; i++)
    System.out.print(c[i]+" ");

edited Dec 01 '13 at 20:04

answered Dec 01 '13 at 19:59

Alexis C.

91,686
21
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177

score 5 · Answer 3 · answered Dec 18 '14 at 14:03

5

  String a[] = { "A", "E", "I" };
  String b[] = { "O", "U" };
  List list = new ArrayList(Arrays.asList(a));
  list.addAll(Arrays.asList(b));
  Object[] c = list.toArray();
  System.out.println(Arrays.toString(c));

answered Dec 18 '14 at 14:03

Karan singh

51
1
1

2

I know the code is pretty clear but it's always best to provide explanation of what you're doing. Plain code with no explanation tends to get flagged for deletion around here. Also - welcome to SO – StormeHawke Dec 18 '14 at 14:09
Thanks @StormeHawke , I am new to this community....will take care in future.... the code was self explanatory so didn't provide comment for it. – Karan singh Dec 26 '14 at 10:21

score 3 · Answer 4 · edited Nov 20 '16 at 21:15

Please try this code, I hope it's useful for you

String a[] = new String[4];
    String b[] = new String[2];
    String[] ab = new String[a.length + b.length];
    int i, j, d, s = 0;
    @SuppressWarnings("resource")
    Scanner x = new Scanner(System.in);
    System.out.println("Enter the first array");

    for (i = 0; i < a.length; i++) {
        a[i] = x.next();
        for (d = i; d < a.length; d++) {
            ab[d] = a[i];
        }
    }

    System.out.println("Enter the second array");

    for (j = 0; j < b.length; j++) {
        b[j] = x.next();
        for (d = a.length + j; d < ab.length; d++)
            ab[d] = b[j];
    }
    System.out.println();
    System.out.println("The new array is !!");
    System.out.println("--------------------");
    for (s = 0; s < ab.length; s++) {
        System.out.print(ab[s] + " ");
    }

score 1 · Answer 5 · answered Jan 28 '18 at 04:05

class MerginTwoArray{
public static void mergingarr(int x[], int y[])
{
    int len=x.length+y.length;
    int arr[]=new int[len];
    //create a variable j which will begin zeroth index of second array
    int j=0;
    for(int i=0; i<arr.length; i++)
    {
        if(i<x.length)
        {
            arr[i]=x[i];
        }
        else
        {
            arr[i]=y[j];
            j++;
        }
    }
    for(int i:arr)
    {
        System.out.print(i+ " ");
    }
}
public static void main(String... args)
{
    mergingarr(new int[]{1,2,3}, new int[]{4,5,6});
}

}

Hope this is clear to you

score 1 · Answer 6 · edited Oct 25 '18 at 03:52

One more way of concatenating 2 arrays is:

System.out.println("Enter elements for a: ");
for (int i = 0; i < 5; i++) {
    int num = in.nextInt();
    a[i] = num;
}

System.out.println("Enter elements for b: ");
for (int i = 0; i < 5; i++) {
    int num = in.nextInt();
    b[i] = num;
}

void merge() {
    int c[] = new int[10];
    System.arraycopy(a, 0, c, 0, a.length);
    System.arraycopy(b, 0, c, a.length, b.length);

    System.out.println(Arrays.toString(c));  // merged array 
}

score 0 · Answer 7 · edited Jan 20 '16 at 12:52

You can use the following:

package array;

public class Combine {

public static void main(String[] args) {

 int[]a = {1,2,3,4};
 int[]b = {4,16,1,2,3,22};
 int[]c = new int[a.length+b.length];
 int count=0;

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

 for(int j=0;j<b.length;j++)
    {
       c[count++]=b[j];
    }

        for(int i=0;i<c.length;i++)
        System.out.print(c[i]+" ");
}

}

score 0 · Answer 8 · answered May 25 '16 at 07:45

Have a look at my solution (you can eventually sort it if need be):

public static int[] mergeAndSortIntArrays(int[] firstInt, int[] secondInt){

    List<Integer> merged = new ArrayList<>();

    for (int i=0; i<firstInt.length; i++){
        merged.add(firstInt[i]);
    }

    for (int i=0; i<secondInt.length; i++){
        merged.add(secondInt[i]);
    }

    Collections.sort(merged);
    int[] result=new int[merged.size()];
    for (int i=0; i<merged.size(); i++){
        result[i]=merged.get(i);
    }
    return result;
}

score 0 · Answer 9 · answered Sep 20 '16 at 06:37

   int a[] = {
        5, 10, 15, 25
    };
    int b[] = {
        12, 5, 7, 9
    };
    int c[] = new int[8];
    for (int i = 0; i < 4; i++) {
        System.out.println(a[i]);

    }
    System.out.println("**************");
    for (int j = 0; j < 4; j++) {
        System.out.println(b[j]);
    }
    //int[] c=merge(a,b);
    for (int i = 0; i < 4; i++) {

        c[i] = a[i];

    }
    for (int i = 0; i < 4; i++) {
        for (int k = 4; k < 8; k++) {
            c[k] = b[i];
        }

    }
    for (int i = 0; i < 4; i++) {
        System.out.println(c[i]);
    }

Some explanation would be nice. – TobiasR. Sep 20 '16 at 06:45 — TobiasR., Sep 20 '16 at 06:45

score 0 · Answer 10 · answered Jul 03 '19 at 08:58

Merge two array without arraylist.

    public class Main {


    static int a[] = {1, 2, 3, 4};
    static int b[] = {5, 6, 7, 8};

    public static void main(String[] args) {

        System.out.println("Hello World!");
        int totalLengh = a.length + b.length;

        int c[] = new int[totalLengh];

        int j = 0;
        for (int i = 0; i < totalLengh; i++) {

            if (i < a.length) {

                c[i] = a[i];

            } else {
                c[i] = b[j];
                j++;
            }

            System.out.println("" + c[i]);
        }
    }
}

Bablu kumar · Answer 11 · 2017-12-19T06:45:27.163

 public class MergeArrays {
    public static void main(String[]args){
         int[] a = {1, 2, 3};
         int[] b = {4, 5, 6};
         int[] c = new int[a.length+b.length];// Here length of int[] c will be 6
         int count = 0;

         //looping to store the value length of i
         for(int i = 0; i<a.length; i++) { 
             c[i] = a[i];
             count++;
          }
        //looping to store the value length of j
          for(int j = 0;j<b.length;j++) { 
             c[count++] = b[j];
          }
        //looping to retrieve the value of c
          for(int i = 0;i<c.length;i++) 
              System.out.print(c[i]);// Displaying looped value/output in single line at console 

    }
}

score -3 · Answer 12 · edited Sep 27 '16 at 20:21

public static void main(String[]args){

        int[]a = {1, 2, 3};
        int[]b = {4, 5, 6};
        int[]c ;
        c=merge(a,b);
        for(int i=0; i<c.length; i++)
            System.out.print(c[i]+" ");
    }
    public static int[]merge(int[]a, int[]b){
        int[]c = new int[a.length+b.length];
        int i;
        for(i=0; i<a.length; i++)
            c[i] = a[i];
        System.out.println(i);
        for(int j=0; j<b.length; j++)
            c[i++]=b[j];
        return c;
    }

Combine two integer arrays into one array in java

12 Answers12

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