Java · Theory

Sorting Collections

Theory

214/270

Sorting Collections

Sorting Collections belongs to the Collections story. List = ordered, duplicates OK (ArrayList). Set = unique (HashSet). Map = key → value (HashMap). Pick by need, not by what you revised last.

For Sorting Collections: ArrayList is the daily List: get(i) is fast, add at end is fast. HashMap lookup by key is average O(1). HashSet is unique values, no duplicates.

Use Sorting Collections with generics: List<String>, Map<String, Integer>. Iterate with for-each or iterator. Don’t use a raw array when the size must grow.

Let's take this on the board with one tiny Main class — no extra files. Sorting Collections — sort uses String's natural compare (case-insensitive here). Start from main, go line by line, and stop at each print. That output is the proof for Sorting Collections.

Exam tip

One class, many Comparators — that's the power.

Example

import java.util.*;
public class Main {
  public static void main(String[] args) {
    List<String> names = Arrays.asList("Ravi", "Asha", "Neha");
    names = new ArrayList<>(names);
    names.sort(String::compareToIgnoreCase);
    System.out.println(names);
  }
}

Sorting Collections — sort uses String's natural compare (case-insensitive here).

Short notes

DefSorting Collections — List = order + duplicates OK. Set = unique. Map = key → value.
RuleSorting Collections — pick it only when that structure matches the problem.
RememberSorting Collections — generics List<String>. ArrayList for daily lists. HashMap for lookup.
TrapSorting Collections — using arrays for everything that must grow, or mixing List/Set/Map.

import java.util.*; public class Main { public static void main(String[] args) { List<String> names = Arrays.asList("Ravi", "Asha", "Neha"); names = new ArrayList<>(names); names.sort(String::compareToIgnoreCase); System.out.println(names); } }

Sorting Collections

Example

Short notes

Questions

Sorting Collections

Example

Short notes

Questions