Array Lists

YESSSS

• An empty list
• To access it, you use special methods
• The data type between the carets <> must be classes (which are usually uppercase)
• Make sure to import it with import java.util.ArrayList;

Class	Not a class
Integer	int
Character	char
Boolean	boolean
String	-
Scanner	-

Instancing

// Making an arraylist variable;
ArrayList<Integer> arrayList = new Arraylist<Integer>();
 
// You can also ignore the type when instancing the array list
ArrayList<Integer> arrayList = new Arraylist<>();

Methods

• add()
• get()
• indexOf()
• remove()
• size()
• set(int i, T replace)
• contains(T other)

Add

arrayList.add(10); // Adds 10 to the array; now size 1
arrayList.add(20); // Adds 20 to the array; now size 2
arrayList.add(0, 1); // Adds 1 at index 0;
arrayList.add(4, 1); // Runtime error, because the array is only of size 3; it's biggest index is 2 and adding another element could at most be index 3. 

String s1 = "Yay";
String s2 = "Boo";
String s3 = s1;
arrayList.add(s1);
arrayList.add(s2);
arrayList.add(s3);
// The arraylist will have 3 "references" but only 2 unique "objects". Changing s1 will change s3. 

Get

int index1 = arrayList.get(1); // Gets the item at index 1 (arrayLists are also indexed from 0 onwards);

Index of

System.out.println(arrayList); // printing arraylists works!
int indexOf10 = arrayList.indexOf(10); // Will find the occurance of 10 in array lists

Remove

// Removes the item in index 2. Everything on the right of index 2 is shifted
arrayList.remove(2);

Size

// Gets the size of the array. Like length or length() in arrays and strings.
arrayList.size();

Set

// Sets index 0 to the value of 1000.
arrayList.set(0, 1000);

Contains

ArrayList<String> myList = new ArrayList<String>();
String s1 = "Hello";
String s2 = "World!";
String s3 = "Hello";
 
myList.add(s1);
myList.add(s2);
// Will be TRUE since s3.equals(s1) should be true even though their addresses are not the same. 
// .contains uses .equals 
System.out.println(myList.contains(s3))

todo CONFIRM

Using them in methods

public static int maxValue(ArrayList<Integer> myList) {
	...
}