public void set(int n, Annotations a) {
    a.throwIfMutable();
    set0(n, a);
  }
Sets the element at the given index. The given element must be immutable.

@param n {@code >= 0, < size();} which index
@param a {@code null-ok;} the element to set at {@code n}
android/android_framework/dex-maker/src/main/java/com/android/dx/rop/annotation/AnnotationsList.java