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up vote 2 down vote favorite

I have this code that duplicates a byte array 5 times. 

class Multiple {
    public static void main(String[] args) {
        byte[] result = new byte[] {0x41,0x42,0x43,0x44};
        int len = result.length;
        byte[] multipled = new byte[len*5];
        for (int i = 0; i < 5; i++) {
            for (int j = 0; j < len; j++) {
                multipled[i*len + j] = result[j];
            }
        } 
        System.out.println(new String(multipled));
        System.out.println(new String(result));
    }
}

Example:

ABCDABCDABCDABCDABCD
ABCD

The code uses multiple loops and assignment, can it be better or shorter?

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migrated from stackoverflow.com Apr 12 at 20:32

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2 Answers 2

up vote 4 down vote accepted

It can be made shorter:

public static void main(String[] args) {
    byte[] result = new byte[] {0x41, 0x42, 0x43, 0x44};
    byte[] multipled = new byte[result.length * 5];
    for (int i = 0; i < multipled.length; i++)
        multipled[i] = result[i % result.length];
    ...
}
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@NexusDuck using new String in this case is necessary, because an array's toString just prints the object address, not the content. –  David Wallace Apr 11 at 20:03
    
@DavidWallace I had no idea. Disregard my comment then –  NexusDuck Apr 11 at 20:05
up vote 2 down vote

This operation is worth defining as a function for clarity and reuse.

To copy an array, use System.arraycopy(). 

public static byte[] repeat(byte[] array, int times) {
    byte[] repeated = new byte[times * array.length];
    for (int dest = 0; dest < repeated.length; dest += array.length) {
        System.arraycopy(array, 0, repeated, dest, array.length);
    }
    return repeated;
}
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