Hey everyone im stuck on a java problem and i could use some help

Code java:

public class Split
{
private ArrayList<Integer> numbers;
public Split()
{
numbers = new ArrayList<Integer>();
numbers.add(1);
numbers.add(5);
numbers.add(21);
numbers.add(43);
numbers.add(60);
numbers.add(70);
numbers.add(80);
numbers.add(90);
numbers.add(100);
}
public ArrayList<Integer> splt(int n);
{
for(int i =0;i<numbers.size();i++){
if(i != n){
return 0;
}else if(i == n){
numbers.IndexOf(i);
}
}

what i need to do is type in a number, if its in the list i created above it splits the array at that position

example:

int = 70

output = firstlist is {1,5,21,43,60}

Secondlist is {70,80,90,100}

i tried searching for the input number in the list if it is not there it returns zero if it is it returns the position of the element in the list