How to fill an array with a vararg with repeat?

Question

I'm looking for an algorithm to fill an array of a specific size with the contents of a vararg, repeating the last element of the vararg until the array is full.

public static <T> T[] fillWithRepeat(int length, T... elements) {
    // make array of length "length" and fill with contents of "elements"
}

Does anyone know a good algorithm for this?

If you don't want to write the loop yourself, use [Arrays.fill](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Arrays.html#fill(java.lang.Object%5B%5D,int,int,java.lang.Object)) — Hulk, Jan 23 '19 at 14:48
I always appreciate when users quickly accept answers, even when its not mine ;-) — GhostCat, Jan 23 '19 at 15:18

GhostCat · Answer 1 · 2019-01-23T14:56:00.417

4

As the question doesn't include any attempt of solving the problem itself, I assume homework, thus the answer is pseudo code only:

create a new array results of length length
iterate index from 0 to length
establish an index2 variable that runs from 0 to elements.length
assign ressult[index] = elements[index2]
either increase index2, or when it reaches elements.length-1, keep it at that value

For creating a "generic" array, see here.

And of course, user Hulk is correct (again), there are utility methods Arrays.fill() and for newer Javas Array.copyOf() that you should consider using.

edited Jan 23 '19 at 14:56

answered Jan 23 '19 at 14:48

GhostCat

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One thing, I can't create an array of a generic type. – HYBR1D Jan 23 '19 at 14:49
Only the last element in the vararg should be repeated, though. – HYBR1D Jan 23 '19 at 14:50
1

@HYBR1D see also [Arrays.copyOf](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Arrays.html#copyOf(T%5B%5D,int)) - you want to copy most of the array, and then fill the remainder – Hulk Jan 23 '19 at 14:52

score 1 · Accepted Answer · answered Jan 23 '19 at 14:55

Here's the algorithm. It also caters for the Generic instantiation problem when you will need to instantiate an array of type T

public static <T> T[] fillWithRepeat(int length, T... elements) {

    List<T> output = new ArrayList<>(Arrays.asList(elements));
    for(int i = 0; i < length - elements.length; i++){
        output.add(elements[elements.length - 1]);
    }

    return output.toArray(elements);
}

How to fill an array with a vararg with repeat?

2 Answers2