ArrayList

Java Chapter 12 - ArrayList

ArrayList is a Java class that provides an automatic resizable array. Normal arrays are not dynamic and cannot be resized after they are created. The ArrayList class includes methods to add, remove, and search for elements. It can be implemented to do database and data structure functions.

12.1 ArrayList Methods

To use the ArrayList class, you must first import java.util.*

Use the following statements to work with the ArrayList class:

Statement	Description
ArrayList<String> myColors = new ArrayList<String>();	Declare a ArrayList of string elements named myColors.
ArrayList<Integer> myNumbers = new ArrayList<Integer>();	Declare a ArrayList of integer elements name myNumbers.
myColors.add("purple"); myColors.add("orange"); myColors.add("green");	Adds an item to the end of the ArrayList. In this case, "purple" is index 0, "orange" is index 1, and "green" is index 2.
myColors.size();	Returns the size of the ArrayList. In this case, the size is 3.
myColors.indexOf("green");	Searches the ArrayList for the string and returns its index of. "green" will return 2. If the string is not found, it will return -1.
myColors.get(1);	Returns the item at index 1. In this case, it returns "orange"
myColors.set(1,"yellow");	Replaces the item at position 1. In this case, "orange" is replaced with "yellow".
myColors.contains("red");	Returns true or false depending if "red" is contained in the ArrayList.
myColors.remove(x);	Removes the item at position x.
myColors.subList(x,y);	Returns a sub list of myColors from position x to position y-1.
myColors.removeRange(x,y);	Removes all elements inclusively between index x and y.
myColors.add(x, item);	Adds an item at position x.
myColors.clear();	Removes all elements in the ArrayList.

12.2 Example ArrayList of Strings

The following is an example program using an ArrayList of Strings:

PeriodicTable.java

import java.util.*;

public class PeriodicTable
{
    public static void main (String[] args)
    {
        ArrayList<String> Elements = new ArrayList<String>();

        Elements.add("hydrogen");   // add elements to the ArrayList
        Elements.add("lithium");
        Elements.add("beryllium");
        Elements.add(1,"helium");   // add helium between hydrogen & lithium

        System.out.println("Size = " + Elements.size());
        System.out.println("Element 2 = " + Elements.get(2));
        System.out.println("Index of beryllium = " + Elements.indexOf("beryllium"));
        System.out.println("Contains carbon?" + Elements.contains("carbon"));
        System.out.println("All Elements: " + Elements);
    }
}

Output

Size = 4
Element 2 = lithium
Index of beryllium = 3
Contains carbon? false
All Elements: [hydrogen, helium, lithium, beryllium]

12.3 Example ArrayList of Objects

The following is an example program using an ArrayList of objects (MonsterClass):

creepy.java

import java.util.*;

public class creepy
{
    static ArrayList<MonsterClass> Monsters = new ArrayList<MonsterClass>();

    public static void main (String[] args)
    {
        Monsters.add(new MonsterClass("Werewolf",100));
        Monsters.add(new MonsterClass("Vampire",150));
        Monsters.add(new MonsterClass("Sasquatch",200));

        System.out.println(Monsters.get(0).Species + " HP = " + Monsters.get(0).HP);
        Monsters.get(0).Damage();
        System.out.println(Monsters.get(0).Species + " HP = " + Monsters.get(0).HP);

        Monsters.remove(0);
    }
}

class MonsterClass
{
    public String Species;
    public int HP;

    MonsterClass (String NewSpecies, int NewHP)
    {
        Species = NewSpecies; HP = NewHP;
    }

    public void Damage()
    {
        HP = HP - 10;
    }
}

Output

Size = 4
Element 2 = lithium
Index of beryllium = 3
Contains carbon? false
All Elements: [hydrogen, helium, lithium, beryllium]