Driver.java

import java.util.*;
import java.io.*;

public class Driver {
    public static void main(String[] args) {
        /*
          ArrayList<String> a = new ArrayList<String>();
          ArrayList<String> b = new ArrayList<String>();
    
          public void fillTime(int n) {
          long startA = System.currentTimeMillis();
          for (int i=0; i<n; i++)
          a.add("x");
          long endA = System.currentTimeMillis();
          long elapsedA = endA-startA;
          System.out.println("a.add('x') "+n+" times takes "+elapsedA);
        
          long startB = System.currentTimeMillis();
          for (int i=0; i<n; i++)
          b.add(0,"x");
          long endB = System.currentTimeMillis();
          long elapsedB = endB-startB;
          System.out.println("b.add(0,'x') "+n+" times takes "+elapsedB);
          System.out.println();
          }
        */

        //a.add("x") was quicker
        //number of strings | time a   |  time b
        //----------------------------------------
        //       10         |     0    |    0
        //      100         |     0    |    0
        //     1000         |     0    |    1
        //     10000        |     1    |    26
        //     100000       |     2    |   853
        //    1000000       |     5    |  124702
        //    10000000      |    104   |  n/a




        /* 2
          ArrayList<String> a = new ArrayList<String>();
          ArrayList<String> b = new ArrayList<String>();

          public void rmvTime(int n) {
          for (int i=0; i<n; i++) {
          a.add("x");
          b.add("x");}
        
          int aS = a.size();
          int bS = b.size();
        
          long startB = System.currentTimeMillis();
          for (int i=bS-1; i>=0; i--) 
          b.remove(i);
          long endB = System.currentTimeMillis();
          long elapsedB = endB-startB;
          System.out.println("b.remove(<end>) "+n+" times takes "+elapsedB);

          long startA = System.currentTimeMillis();
          for (int i=0; i<aS; i++) 
          a.remove(0);
          long endA = System.currentTimeMillis();
          long elapsedA = endA-startA;
          System.out.println("a.remove(0) "+n+" times takes "+elapsedA);
          System.out.println();
          }
        */

        //b.add(<end>) was quicker
        //number of strings |  time a  |  time b
        //----------------------------------------
        //       10         |     0    |    0
        //      100         |     0    |    0
        //     1000         |     1    |    0
        //     10000        |    23    |    1
        //     100000       |    453   |    1
        //    1000000       |   9382   |    2
        //    10000000      |   n/a    |   25
        
        



        ArrayList<Integer> a = new ArrayList<Integer>();
        for (int i=0; i<22; i++)
            a.add(i*7);
        
        System.out.println(a);
        //reverse
        for (int i=0; i<(a.size()/2); i++) {
            int temp = (int)a.get(a.size()-1-i);
            a.set(a.size()-1-i,a.get(i));
            a.set(i,temp);
        }
        
        System.out.println(a);
    }
}