Java – using collections Sort()

I have to write a method to sort integers and doubles

public ArrayList<Number> sortDescending(ArrayList<Number> al){
    Comparator<Number> c=Collections.reverSEOrder();
    Collections.sort(al,c);
    return al;
}

public ArrayList<Number> sortAscending(ArrayList<Number> al){
    Collections.sort(al);
    return al;
}

The problem is that in sortascending, the following error occurs:

Solution

You need to use the general upper limit of the number intersecting the comparable < T >:

public <T extends Number & Comparable<T>> ArrayList<T> sortDescending(ArrayList<T> al){
    Comparator<T> c=Collections.reverSEOrder();
    Collections.sort(al,c);
    return al;
}

public <T extends Number & Comparable<T>> ArrayList<T> sortAscending(ArrayList<T> al){
    Collections.sort(al);
    return al;
}

All JDK numbers (such as float, integer, etc.) match this type

For inexperienced people, syntax < T extends a & B is the way you bind t to a and B For reference only, there is no grammar of "or" logic (it doesn't make sense if you consider it)