Java 11_ArrayList

ArrayList

import arraylist libraries

import java.util.ArrayList; // The ArrayList library
import java.util.Iterator; // The Iterator Library
import java.util.Arrays; // The Arrays Library

Create an ArrayList variable

        // You don't have to declare the ArrayList size like you
        // do with arrays (Default Size of 10)
    
        // You can create the ArrayList on one line
        
        ArrayList arrayListTwo = new ArrayList();
        
        // You can also define the type of elements the ArrayList
        // will hold
        ArrayList<String> names = new ArrayList<String>();

Add elements to an ArrayList

        names.add("John Smith");
        names.add("Mohamed Alami");
        names.add("Oliver Miller");
        
        // add an element in a specific position
        names.add(2, "Jack Ryan");
        

Retrieve values in an ArrayList with get

        // arrayListName.size() returns the size of the ArrayList
        for( int i = 0; i < names.size(); i++)
        {
            System.out.println(names.get(i));
        }

Replace a value using the set method

        names.set(0, "John Adams");

Remove an item with remove

        names.remove(3);

You can also remove the first and second item with the removeRange method

 names.removeRange(0, 1);

Print out the ArrayList itself use the toString method

        System.out.println(names);

You can also use the enhanced for with an ArrayList

        for(String i : names)
        {
            System.out.println(i);
        }
        System.out.println(); 

Use an iterator to print out values in an ArrayList

        // Creates an iterator object with methods that allow
        // you to iterate through the values in the ArrayList
        Iterator indivItems = names.iterator();
        
        // When hasNext is called it returns true or false
        // depending on whether there are more items in the list
        
        while(indivItems.hasNext())
        {
            // next retrieves the next item in the ArrayList
            System.out.println(indivItems.next());
            
        }

Copy in Arrays

    // I create an ArrayList without stating the type of values
    // it contains (Default is Object)
    ArrayList nameOne = new ArrayList();

    // addAll adds everything in name to nameOne
    nameOne.addAll(names);
    System.out.println(nameCopy);

Contains returns a boolean value based off of whether the ArrayList contains the specified object

        if(names.contains(paulYoung))
        {
            System.out.println("Paul is here");
        }
        
        // containsAll checks if everything in one ArrayList is in
        // another ArrayList
        if(names.containsAll(nameOne))
        {
            System.out.println("Everything in nameOne is in names");
        }

Deletes everything in the ArrayList

        names.clear();
        
        // isEmpty returns a boolean value based on if the ArrayList 
        
               // is empty(check)
        if (names.isEmpty())
        {
            
            System.out.println("The ArrayList is empty");
            
        }

ToArray & ToString

    Object[] moreNames = new Object[4];

    // toArray converts the ArrayList into an array of objects
    moreNames = nameOne.toArray();
    
    // toString converts items in the array into a String
    System.out.println(Arrays.toString(moreNames));