How does the removal of elements from ArrayList occur and how does its size change in this case?

When removing an element from the middle or beginning of a list, elements with higher indices shift to the left, filling the vacated position.

// Example of removing an element by index
ArrayList<String> list = new ArrayList<>(Arrays.asList("A", "B", "C", "D"));
list.remove(1); // Removing element "B"
// Now the list: ["A", "C", "D"]

When removing an element by value, the first occurrence of that element is found, and a similar shift occurs.

// Example of removing an element by value
ArrayList<String> list = new ArrayList<>(Arrays.asList("A", "B", "C", "B"));
list.remove("B"); // Removing the first occurrence of "B"
// Now the list: ["A", "C", "B"]

Removing an element from the end of the list does not require shifting elements. The size simply decreases.

// Example of removing an element from the end
ArrayList<String> list = new ArrayList<>(Arrays.asList("A", "B", "C"));
list.remove(list.size() - 1); // Removing element "C"
// Now the list: ["A", "B"]

In any case, upon successful removal of an element, the logical size of the list (returned by the size() method) decreases by one. The array underlying the ArrayList does not physically shrink immediately, but during the next addition, memory may be reallocated (capacity increase) if the current capacity is insufficient.