Error in the interlayer method elements with Mergesort in a List<Integer>

Question

This part of the algorithm has the function of bridging the elements of a List<Integer> (list of normal integers) using the Mergesort sorting algorithm. ERROR ON LINE 7

private static List intercalar(List<Integer> list, int l, int h, int r){
    int i = l, j = h, /*marcador do topo*/t = 0; 
    List<Integer> topo = Arrays.asList(); 

    while(i < h && j < r){ // O(n/2) = 
        if(list.get(i) < list.get(j)){ 
            topo.add(t, list.get(i)); **ERRO AQUI**
            i++; 
        } else { 
            topo.add(t, list.get(j));
            j++; 
        } 
        t++;
    } 

    //anexa o restante das cartas(as cartas q ficaram sozinhas)
    while(i < h){
        topo.add(t, list.get(i));
        t++;
        i++;
    }
    while(j < r){
        topo.add(t, list.get(j));
        t++;
        j++;
    } 

    for(i = l, t = 0 ; i < r ; i++, t++) {
        list.set(i, topo.get(t));
    } 
    return list;
} 

Displays the following error :

java.util.Unsupportedoperationexception:null (in java.util.Abstractlist)

Answer 1

Arrays.asList(); 

It works as follows, if you have an object vector you want to allocate in a list as for example:

int[] vet = new int[]{1,2,3,4,5};
List<int> list1 = Arrays.asList(vet);

In this case I have put a size 5 vector in a list, in your case you are not allocating anything in the list, so it is giving error because your list is empty. Something else I’ve been watching your code and I’ve seen that you’re trying to manipulate the list as if it were a map :

 topo.add(t, list.get(i)); **ERRO AQUI**
    i++; 
 } else { 
    topo.add(t, list.get(j));

Switch to this:

 topo.add(list.get(i)); **ERRO AQUI**
    i++; 
 } else { 
    topo.add(list.get(j));

Or just use it:

List<int> topo = new ArrayList<int>();