class Ideone {
  public static void main (String[] args) throws java.lang.Exception {
    Integer a[] = {1,2,3,4,5,6,7};
    int b[] = {1,2,3,4,5,6,7};

    Arrays.sort(a, (x,y) -> y-x);
    //Arrays.sort(b, (x,y) -> y-x);

    System.out.println(Arrays.toString(a));
    System.out.println(Arrays.toString(b));
  }
}

Main.java:11: error: no suitable method found for sort(int[],(x,y)->y - x)
    Arrays.sort(b, (x,y) -> y-x);
          ^
    method Arrays.<T#1>sort(T#1[],Comparator<? super T#1>) is not applicable
      (inference variable T#1 has incompatible bounds
        equality constraints: int
        upper bounds: Object)
    method Arrays.<T#2>sort(T#2[],int,int,Comparator<? super T#2>) is not applicable
      (cannot infer type-variable(s) T#2
        (actual and formal argument lists differ in length))
  where T#1,T#2 are type-variables:
    T#1 extends Object declared in method <T#1>sort(T#1[],Comparator<? super T#1>)
    T#2 extends Object declared in method <T#2>sort(T#2[],int,int,Comparator<? super T#2>)
Note: Some messages have been simplified; recompile with -Xdiags:verbose to get full output
1 error

b = IntStream.of(b)
    .boxed()
    .sorted(Comparator.reverseOrder())
    .mapToInt(i -> i)
    .toArray();

Primitive.sort(b, (i1, i2) -> Double.compare(i2, i1), false);