[WainWright]

I can imagine many ways to do this but the simplest one I have is to simply sort the array in ascending order and then subtract the last element from the first.

Code

Arrays.sort(numbers);//Arrays.parallelSort(numbers);
return numbers[4] - numbers[0];//return numbers[numbers.length - 1] - numbers[0];

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I don't know if performance would be better to manually find the largest and smallest or not. Sometimes the methods Oracle provides are more efficient.

[Enchanter]

In Java8 you can do

Code

public static int getMaxAd(int[] arr){
        return Arrays.stream(IntStream.range(0, arr.length - 1).toArray())
                  .map(x -> arr[x + 1] - arr[x])
                  .max().getAsInt();
    }

So

Code

int max = getMaxAd(numbers);