Week 2: Methods, strings and lists/15a Lists

An example of a program that creates a list and stores five strings in it:

import java.util.ArrayList;

public class Example {
    public static void main(String[] args) {

        // ArrayList datatype
        // each element: String datatype
        // list name: names
        // 'new' - initialise list object
        ArrayList<String> names = new ArrayList<>();

        names.add("Jack Java");
        names.add("Paula Python");
        names.add("Cinthia C");
        names.add("Randy Rust");
        names.add("Pia PHP");

        System.out.println(names);
    }
}


 

Program outputs:
[Jack Java, Paula Python, Cinthia C, Randy Rust, Pia PHP]




==============================================



List type
- List can store elements of various 'basic type'
- BUT type SPECIFICATION - CANT USE 'basic type'
- SPECIFICATION - need to use 'envelope class'

Basic type |	Correspoding envelope class
int	             Integer
double	         Double
char		     Character
boolean		     Boolean
float		     Float




ArrayList<String> participants = new ArrayList<>();
participants.add("Ann Attendee");

ArrayList<Integer> results = new ArrayList<>();
results.add(3);

ArrayList<Character> chars = new ArrayList<>();
chars.add('x');







==============================================


list elements




add
ArrayList<String> attendees = new ArrayList<>();
attendees.add("Ann Attendee");
System.out.println(attendees); //[Ann Attendee]


attendees.add("Alex Attendee");
attendees.add("Winry Winner");
System.out.println(attendees); //[Ann Attendee, Alex Attendee, Winry Winner]


Program outputs:
[Ann Attendee]
[Ann Attendee, Alex Attendee, Winry Winner]









get
ArrayList<String> attendees = new ArrayList<>();
attendees.add("Ann Attendee");
attendees.add("Alex Attendee");
attendees.add("Winry Winner");

System.out.println(attendees.get(0)); //Ann Attendee
System.out.println(attendees.get(2)); //Winry Winner



// create new empty list
ArrayList<Integer> numbers = new ArrayList<>();
// from i=1 to 10, populate list with the 'multiple of 10'
for (int i=1; i<=10; i++) {
    numbers.add(i * 10);
}

System.out.println(numbers);
System.out.println(numbers.get(0) + ", " + numbers.get(1));
System.out.println(numbers.get(9));



Program outputs:
Ann Attendee
Winry Winner
[10, 20, 30, 40, 50, 60, 70, 80, 90, 100]
10, 20
100












add AT SPECIFIC IDX
remove

ArrayList<Double> results = new ArrayList<>();
results.add(1.0);
results.add(2.5);
results.add(8.5);

System.out.println(results); //[1.0, 2.5, 8.5]


results.add(0, 9.9); // add to start
System.out.println(results); //[9.9, 1.0, 2.5, 8.5]

results.add(1, 10.0); // add to index 1
System.out.println(results); //[9.9, 10.0, 1.0, 2.5, 8.5]

results.remove(0);  // remove the first
System.out.println(results); //[10.0, 1.0, 2.5, 8.5]

results.remove(3); // remove from index 3
System.out.println(results); //[10.0, 1.0, 2.5]

Program outputs:
[1.0, 2.5, 8.5]
[9.9, 1.0, 2.5, 8.5]
[9.9, 10.0, 1.0, 2.5, 8.5]
[10.0, 1.0, 2.5, 8.5]
[10.0, 1.0, 2.5]