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Efficient Algorithms Inside Java’s Core Libraries

How Java’s Standard Libraries Stay Fast and Efficient?

Skilled Coder
4 min readFeb 14, 2025

Java’s standard libraries use smart, optimized algorithms to ensure efficiency and performance. Here’s a look at some lesser-known but powerful algorithms that keep Java running smoothly.

TimSort (Used in Arrays.sort() for Objects)

Library: java.util.Arrays

A hybrid sorting algorithm derived from Merge Sort and Insertion Sort. TimSort takes advantage of real-world data that often has ordered runs and performs exceptionally well on partially sorted data.

Why It’s Efficient?

  • Best case O(n): If the array is already sorted, it performs a single pass.
  • Average case O(n log n): It uses Merge Sort for the main sorting and Insertion Sort for small segments.
  • Optimized for real-world data: Unlike pure QuickSort or MergeSort, it adapts dynamically based on input data.
import java.util.Arrays;

public class TimSortExample {
public static void main(String[] args) {
Integer[] arr = {5, 2, 9, 1, 5, 6};
Arrays.sort(arr); // Internally uses TimSort for objects
System.out.println(Arrays.toString(arr));
}
}

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Skilled Coder
Skilled Coder

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