Sorting an ArrayList in AP CSA

The AP exam tests both using Collections.sort() for built-in sorting and implementing selection sort or insertion sort manually — usually on arrays. Know both.

Collections.sort() for ArrayLists

import java.util.ArrayList;
import java.util.Collections;

ArrayList nums = new ArrayList<>();
nums.add(5); nums.add(2); nums.add(8); nums.add(1);

Collections.sort(nums);   // ascending order
System.out.println(nums); // [1, 2, 5, 8]

Selection Sort (Arrays — AP Required)

Finds the minimum in the unsorted section and swaps it into position. O(n²) time.

int[] arr = {5, 2, 8, 1, 9};

for (int i = 0; i < arr.length - 1; i++) {
    int minIdx = i;
    for (int j = i + 1; j < arr.length; j++) {
        if (arr[j] < arr[minIdx]) {
            minIdx = j;
        }
    }
    // Swap arr[i] and arr[minIdx]
    int temp = arr[i];
    arr[i] = arr[minIdx];
    arr[minIdx] = temp;
}