Vocab

Array

collection of similar data types

Elements

each variable in an array

Index and Array Length

Index: what value/position is assigned to each element
Array length: how many elements in the array

Introductions

A reference type
Array cannot be modified while ArrayLists can change size dynamically

Methods

add(int index, element) ...

Traversing ArrayLists

For Loop
While Loop
Enhanced ForLoop

Searching

The locating of data within linear structures
Searching a structure involves control structures - iterationnal and selection - loop with an if statement
For loops are optimal for linear searching because each element needs to be specified sequentiallly with no need to trcak the index after its executed
Order matters sometimes in searching

Sorting

Sorting sorts the ArrayList in a specified order (ascending or descending)
Collections.sort[(list.name)] - sort in ascending order
Collections.sort[(ArrayList,Collections.reverseOrder())] - sort in ascending order

HW

Create an ArrayList that includes 2 of the 4 factors listed below.

Sort an ArrayList in descending order and swap the first and last elements Find and display the hashCode of an Arraylist before and after being sorted Return "ascending" if the list is sorted in ascending order, return "descending" if it is descending, and return "neither" if neither Replace 3 elements in an ArrayList with another ArrayList and reverse the order of the new list

Return "ascending" if the list is sorted in ascending order, return "descending" if it is descending, and return "neither" if neither

import java.util.*;
import java.util.Collections;

public class Main  {

  public static void main(String args[]){
    ArrayList<Integer> numbers = new ArrayList<Integer>();
    numbers.add(2);
    numbers.add(6);
    numbers.add(3);
    numbers.add(7);

    /*Unsorted List: ArrayList content before sorting*/
    System.out.println("Before Sorting:");
    for(Integer num: numbers){
      System.out.println(num);
    }

    /* Sorting in decreasing order*/
    Collections.sort(numbers, Collections.reverseOrder());

    /* Sorted List in reverse order*/
    System.out.println("In descending order:");
    for(Integer num: numbers){
      System.out.println(num);
    }

    Collections.swap(numbers, 0, 3);
    System.out.println("Swap first and last:");
      System.out.println(numbers);
  }
}

Main.main(null);

Before Sorting:
2
6
3
7
In descending order:
7
6
3
2
Swap first and last:
[2, 6, 3, 7]

Check if ArrayList is ascending or descending

class Main1
{
    public static boolean isSorted(int[] num)
    {
        if (num == null || num.length <= 1) {
            return true;
        }
 
        for (int i = 0; i < num.length - 1; i++)
        {
            if (num[i] > num[i + 1]) {
                return false;
            }
        }
 
        return true;
    }
 
    public static void main(String[] args)
    {
        int[] num = { 1, 2, 3, 4, 5 };
        System.out.println(isSorted(num));        // true
    }
}

Main1.main(null)

true