Removing the last element of an ArrayList

Question

I'm new to Java and I'm stuck with an exercise I've been trying to solve for over a week now and I don't know what I'm doing wrong.

I need to delete the last elements of an ArrayList, an integer in this case.

The problem is that when I run the test, it still returns the old values.

public static void removeLastOccurrence(int x, ArrayList<Integer> list) {
    if (list != null && !list.isEmpty()) {
       list.remove(list.size()-1);
    }
}

I also tried using list.remove(list.lastIndexOf(x));

But it still returns the same list when I run this test.

public class UTest{
    @Test
    public void testMultipleLast() {
        ArrayList<Integer> input = new ArrayList<Integer>(asList(1,1,3,5,7,1,5,9,1));
        ArrayList<Integer> result = new ArrayList<Integer>(asList(1,1,3,5,7,1,5,9));
        Solution.removeLastOccurence(1, input);
        assertEquals(result, input);
    }
}

Would be nice if someone could help and tell me what I'm missing as it's getting quite frustrating as I've the feeling that I'm just missing a small piece of the puzzle.

Answer 1

Your test should be like below. In the test code in the original post, you are not actually invoking the method that you are trying to test.

public class UTest
{
  @Test
  public void testMultipleLast() {
     ArrayList<Integer> input = new ArrayList<Integer>(asList(1,1,3,5,7,1,5,9,1));
     ArrayList<Integer> result = new ArrayList<Integer>(asList(1,1,3,5,7,1,5,9));

     // int x = ?
     ArrayList<Integer> actual = SomeClass.removeLastOccurrence(x, input)
     assertEquals(result, actual);
  }
 }

and the removeLastOccurrence() method can do the following

if(list != null && !list.isEmpty()){
    list.remove(list.size() - 1);
}

Answer 2

You have to use :

list.remove(list.size()-1);

And return your new list so you can use :

public static ArrayList<Integer> removeLastOccurrence(int x, ArrayList<Integer> list) {
    if (list != null && !list.isEmpty()) {
       list.remove(list.size()-1);
    }
    return list;
}

Answer 3

It's because you are not removing any elements.

list.get(list.size()-1);

does not remove elements.

use

list.remove(list.size()-1)

instead.

Answer 4

According to Java ArrayList API with get(int index) method you just obtain the element in index position in your ArrayList. This is the method you are looking for:

public static void removeLastOccurrence(int x, ArrayList<Integer> list) {
    if (list != null && !list.isEmpty()) {
        list.remove(list.size()-1);
    }
}

Answer 5

If you pass your list as argument to the method it becomes a local variable. Therefore you are not removing the element from your input list but only from the local variable list . The solution is to return that local list from your method or to remove the element directly from your "input" list using the same code. The x parameter in your original method is unnecessary.