Insertion, Removal, and Search

Most AP-style list problems don't use a single ArrayList method in isolation — they chain them. First, search for an element's position. Then, depending on whether it was found, either insert a new value or remove an existing one.

The three operations work together:

• Search answers "where is it?" (returns an index, or -1).
• Insertion places a new element at a chosen position.
• Removal deletes an element at a given position.

On the AP exam, this combined pattern appears in FRQs about managing rosters, inventories, schedules — anywhere objects come and go based on lookup.

Manual sequential search

public int indexOfName(ArrayList<Student> list, String target) {
    for (int i = 0; i < list.size(); i++) {
        if (list.get(i).getName().equals(target)) {
            return i;
        }
    }
    return -1;
}

Returns the index of the first match, or -1 when not found. The standard AP CSA contract for search methods.

Insertion at a specific position

list.add(index, newItem);   // shifts existing elements right

Common positions: 0 (front), list.size() (back — same as add(item)), or somewhere in the middle based on logic.

Removal at a specific position

list.remove(index);   // shifts later elements left

Combined: search-then-remove

public void removeStudent(ArrayList<Student> list, String name) {
    int i = indexOfName(list, name);
    if (i != -1) {
        list.remove(i);
    }
}

The if (i != -1) guard is essential. Without it, passing -1 to remove throws an exception.

Combined: search-then-insert-after

public void insertAfter(ArrayList<Student> list, String target, Student newStudent) {
    int i = indexOfName(list, target);
    if (i != -1) {
        list.add(i + 1, newStudent);
    }
}

Inserting at i + 1 places the new element directly after the matched one. Edge case: if i + 1 == list.size(), the insertion happens at the end — which add handles naturally.