How to merge two arrays into one in Java

Javaarray Merging arrays

Directory (?) [+]

1. A apache-commons
2. Two systemarraycopy
3. Three arrayscopyof
4. Four arraynewinstance

Http://freewind.me/blog/20110922/350.html

In Java, how do you merge two String[] into one?

It seems to be a very simple question. But how to write the code efficiently and concisely is still worth thinking about. Here are four methods, please refer to the selection.

First, Apache-commons

This is the simplest way. In Apache-commons, there is a ArrayUtils.addAll(Object[], Object[]) way to get our line done:

String[] both = (String[]) ArrayUtils.addAll(first, second);

Everything else needs to be packaged by invoking the methods provided in the JDK.

For convenience, I will define a tool method concat that can combine two numbers together:

static String[] concat(String[] first, String[] second) {}

For general purposes, I will use generics to define it, where possible, so that not only String[] can it be used, but other types of arrays can also be used:

static <T> T[] concat(T[] first, T[] second) {}

Of course, if your JDK doesn't support generics, or you can't use them, you can replace T with a manual String .

Second, system.arraycopy () [Java]View Plaincopyprint?

1. Static string[] Concat (string[] A, string[] b) {
2. String[] c= new string[a.length+b.length];
3. System.arraycopy (A, 0, C, 0, a.length);
4. System.arraycopy (b, 0, C, A.length, b.length);
5. return C;
6. }

Static string[] Concat (string[] A, string[] b) {   string[] c= new string[a.length+b.length];   System.arraycopy (A, 0, C, 0, a.length);   System.arraycopy (b, 0, C, A.length, b.length);   return c;}

Use the following:

String[] both = concat(first, second);

Third, arrays.copyof ()

In Java6, there is a method Arrays.copyOf() that is a generic function. We can use it to write a more general method of merging:

[Java]View Plaincopyprint?

1. Public static <T> t[] Concat (t[] First, t[] second) {
2. T[] result = arrays.copyof (First, first.length + second.length);
3. System.arraycopy (second, 0, result, first.length, second.length);
4. return result;
5. }

public static <T> t[] Concat (t[] First, t[] second) {  t[] result = arrays.copyof (First, first.length + second.le Ngth);  System.arraycopy (second, 0, result, first.length, second.length);  return result;}         

If you want to merge multiple, you can write this:

[Java]View Plaincopyprint?

2. Public static <T> t[] Concatall (t[] First, t[] ... rest) {
4. int totallength = first.length;
6. For (t[] array:rest) {
8. Totallength + = Array.Length;
10. }
12. T[] result = arrays.copyof (first, totallength);
14. int offset = first.length;
16. For (t[] array:rest) {
18. System.arraycopy (Array, 0, result, offset, array.length);
20. Offset + = Array.Length;
22. }
24. return result;
26. }

public static <T> t[] Concatall (t[] First, t[] ... rest) {  int totallength = first.length;  For (t[] array:rest) {    totallength + = Array.Length;  }  T[] result = arrays.copyof (first, totallength);  int offset = first.length;  For (t[] array:rest) {    system.arraycopy (array, 0, result, offset, array.length);    Offset + = Array.Length;  }  return result;}

Use the following:

String[] both = concat(first, second);String[] more = concat(first, second, third, fourth);

Iv. array.newinstance

You can also use Array.newInstance to generate an array:

[Java]View Plaincopyprint?

2. Private static <T> t[] Concat (t[] A, t[] b) {
4. final int alen = a.length;
6. final int blen = b.length;
8. if (alen = = 0) {
10. return B;
12. }
14. if (Blen = = 0) {
16. return A;
18. }
20. final t[] result = (t[]) Java.lang.reflect.Array.
22. Newinstance (A.getclass (). Getcomponenttype (), Alen + Blen);
24. System.arraycopy (A, 0, result, 0, Alen);
26. System.arraycopy (b, 0, result, Alen, Blen);
28. return result;
30. }

How to merge two arrays into one in Java