How to Sort Multiple ArrayLists Together in Java?

Question

What are the best ways to sort multiple ArrayLists together in Java?

List<String> list1 = Arrays.asList("apple", "orange", "banana");
List<Integer> list2 = Arrays.asList(3, 1, 2);

Map<String, Integer> combined = new HashMap<>();
for (int i = 0; i < list1.size(); i++) {
    combined.put(list1.get(i), list2.get(i));
}

List<Map.Entry<String, Integer>> entryList = new ArrayList<>(combined.entrySet());
entryList.sort(Map.Entry.comparingByKey()); // Sort by keys

List<String> sortedKeys = new ArrayList<>();
List<Integer> sortedValues = new ArrayList<>();
for (Map.Entry<String, Integer> entry : entryList) {
    sortedKeys.add(entry.getKey());
    sortedValues.add(entry.getValue());
}

Answer

Sorting multiple ArrayLists together in Java can be achieved through various methods that ensure data integrity and consistency across lists. This technique involves creating a combined structure that retains the relationships between the elements of the lists being sorted.

import java.util.*;

public class MultiListSort {
    public static void main(String[] args) {
        List<String> names = Arrays.asList("Alice", "Bob", "Charlie");
        List<Integer> scores = Arrays.asList(90, 95, 85);

        List<Pair> pairs = new ArrayList<>();
        for (int i = 0; i < names.size(); i++) {
            pairs.add(new Pair(names.get(i), scores.get(i)));
        }

        pairs.sort(Comparator.comparing(Pair::getName)); // Sort by name

        for (Pair pair : pairs) {
            System.out.println(pair.getName() + " : " + pair.getScore());
        }
    }
}

class Pair {
    private String name;
    private int score;

    public Pair(String name, int score) {
        this.name = name;
        this.score = score;
    }

    public String getName() {
        return name;
    }

    public int getScore() {
        return score;
    }
}

Causes

ArrayLists need to be sorted based on a corresponding relationship, such as names and their associated IDs.
Inconsistent sorting when sorting lists independently may lead to a mismatch in data.

Solutions

Combine the ArrayLists into a single data structure like a Map or a List of custom objects.
Sort that combined structure and separate them back into individual lists after the sorting is done.

Common Mistakes

Mistake: Sorting lists independently without maintaining data integrity.

Solution: Always combine lists into a cohesive structure before sorting.

Mistake: Assuming the order of elements in separate lists matches after sorting.

Solution: Ensure to use data structures that preserve correlation between elements of different lists.

Helpers

Java sort ArrayLists
sort multiple ArrayLists in Java
Java ArrayList sorting techniques
combine ArrayLists and sort Java