taylorialcom/ DataStructures

Introduction to ArrayLists

An ArrayList is a class that encapsulates an array and provides a number of convenient methods to simplify storing collections of like data.

Introduction

Examples

Consider the following two methods. Both of these methods reverse the order of the elements of an ArrayList<String>, and yet they are quite different.

public static ArrayList<Double> reverse1(ArrayList<Double> data) {
  ArrayList<Double> temp = new ArrayList();
  for(int i = data.size()-1; i >= 0; i--){
    temp.add(data.get(i));
  }
  return temp;
}

public static ArrayList<Double> reverse2(ArrayList<Double> data) {
  for(int i=0; i < data.size()/2; i++){
    int j = data.size()-1-i;
    Double temp = data.get(i);
    data.set(i, data.get(j));
    data.set(j, temp);
  }
  return data;
}