How to concatenate 2 or more strings as one inside a string array in Java?

Question

I'd like to concatenate 2 or more consecutive strings into one string in an array according to two variables x and y meaning that starting from the x:th element, concatenate, until we have concatenated y elements. For example, if an Array 'A' has elements as:

A = {"europe", "france", "germany", "america"};
x=2;y=2;
//Here, I want to concatenate france and germany as :
A = {"europe", "france germany", "america"};
//Or 
x=2,y=3;

A= {"europe", "france germany america"};

Like this. Anyone know How This can be done without complex programming?

Answer 1

Probably the most concise way is:

1. Construct an array of the right size:

   String[] result = new String[A.length - (y-1)];
   

2. Copy the start and the end of the array using System.arraycopy:

   System.arraycopy(A, 0, result, 0, x-1);
   System.arraycopy(A, x+y-1, result, x+1, A.length-(x+1));
   

3. Build the concatenated string:

   result[x-1] = String.join(" ", Arrays.asList(A).subList(x-1, x-1+y));
   

(Note: out by one errors may be present, owing to the date of writing)

Answer 2

Here is a working script, though I don't know how simple you would consider it to be. The algorithm is to simply walk down the input array, copying over strings to the output, until we reach the first entry as determined by the x value. Then, we concatenate the y number of terms to a single string. Finally, we finish by copying over the remaining terms one-by-one.

public static String[] concatenate(String[] input, int x, int y) {
    List<String> list = new ArrayList<>();
    // just copy over values less than start of x range
    for (int i=0; i < x-1; ++i) {
        list.add(input[i]);
    }

    // concatenate y values into a single string
    StringBuilder sb = new StringBuilder("");
    for (int i=0; i < y; ++i) {
        if (i > 0) sb.append(" ");
        sb.append(input[x-1+i]);
    }
    list.add(sb.toString());

    // copy over remaining values
    for (int i=x+y-1; i < input.length; ++i) {
        list.add(input[i]);
    }
    String[] output = new String[list.size()];
    output = list.toArray(output);

    return output;
}

String[] input = new String[] {"europe", "france", "germany", "america"};
int x = 2;
int y = 3;
String[] output = concatenate(input, x, y);
for (String str : output) {
    System.out.println(str);
}

Demo