How to solve these three methods in java on lists?

See more:

Java

I'm practicing programming in java with lists, because in a while this exam. i can't solve 3 methods

1st: Write a method, belonging to a hypothetical list of numbers, which concatenates the L2 list passed as an argument to the end of the current list.

2nd: Write a method, belonging to a hypothetical list of numbers, which searches for an element and returns a new list containing the numbers corresponding to the position in which the element appears in the given list. For example if L is 1 -> 15 -> 1 -> 9 -> 8 -> 1 and the element to search is 1, then the method returns the list of positions where 1 is present in the list L. The returned list, in this case is: 1 -> 3 -> 6 (I have separated 2 methods one, "search" and the other "modify") Here I wrote:

What I have tried:

1st method I wrote:

public void concatenazione(Lista L,Lista L2) {
    Nodo p=head;
    while(p.getLink()!=null) {
        p=p.setLink(p);
        p=p.getLink();
    }
}

2nd method I wrote:

public int ricerca(int ricerca) {
    Nodo p=head;
    int i=0;
    while(p.getLink()!=null) {      //Scorri la lista
        if(p.getElemento()==ricerca) {
            System.out.print(i++);
        }
        p=p.getLink();  //scorimento
        i++;
    }
    return i++;
}

public void modificare(Nodo L) {
    L=head;
    int disparo=0;
    while(L.getLink()!=null) {
        if(L.getElemento()/2==1) {
            L.setElemento(disparo);
            L.getLink().getLink();  //riferisce al prossimo nodo
            L.setElemento(disparo);
        }
        L=L.getLink();      //Scorimento
    }
}