http://stackoverflow.com/questions/19634692/java-arraylist-size-declaration-and-performance

Capacity Increase Benchmark

package de.jungblut.benchmark;

import java.util.ArrayList;

import com.google.caliper.Param;
import com.google.caliper.Runner;
import com.google.caliper.SimpleBenchmark;

public class PerfectSquaresBenchmark extends SimpleBenchmark {

  @Param
  InitType type;

  public enum InitType {
    DEFAULT, INIT
  };

  ArrayList<Integer> result;

  private int[] arr;

  @Override
  protected void setUp() throws Exception {

    arr = new int[5000000];
    for (int i = 0; i < arr.length; i++) {
      arr[i] = i + 1;
    }
    newList();
  }

  public void newList() {
    switch (type) {
      case DEFAULT:
        result = new ArrayList<>();
        break;
      case INIT:
        result = new ArrayList<>(5_000_000);
        break;
      default:
        break;
    }
  }

  public void perfectSquares(int[] arr) {
    for (int i = 0; i < arr.length; i++) {
      double root = Math.sqrt(arr[i]);
      int irt = (int) Math.floor(root);
      if (irt * irt == arr[i]) {
        result.add(arr[i]);
      }
    }
  }

  public void timeAppend(int reps) {
    for (int rep = 0; rep < reps; rep++) {
      newList();
      perfectSquares(arr);
      System.out.println(result.size());
    }

  }

  public static void main(String[] args) {
    Runner.main(PerfectSquaresBenchmark.class, args);
  }
}