Records, Lists & Tuples (OCR AS Computer Science): Revision Note

Records

What is a record?

• A record is a row in a file and is made up of fields

• They are used in databases as shown in the example below

• The above example contains 3 records, where each record has 3 fields. A record can be declared as follows

Example in Pseudocode

personDataType = record
 integer ID
 string firstName
 string surname
endRecord 

Example in Python

class Person:
    def __init__(self, ID, firstName, surname):
        self.ID = ID
        self.firstName = firstName
        self.surname = surname

# Creating an instance of the Person record
person_record = Person(1, "Tony", "Smith")

# Accessing the fields of the Person record
print("ID:", person_record.ID)
print("First Name:", person_record.firstName)
print("Surname:", person_record.surname)

• In the code above, a class is defined called “Person” with an ‘__init__’ method that initialises the fields of the record

• Create an instance of the “Person” record called ‘person_record’ with an ID of 1, first name “Tony”, and surname “Smith”

• Finally access and print the values of the fields using dot notation (‘object.field’)

Example in Java

public class Person {
    private int ID;
    private String firstName;
    private String surname;

    public Person(int ID, String firstName, String surname) {
        this.ID = ID;
        this.firstName = firstName;
        this.surname = surname;
    }

    public int getID() {
        return ID;
    }

    public String getFirstName() {
        return firstName;
    }

    public String getSurname() {
        return surname;
    }

    public void setID(int ID) {
        this.ID = ID;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public void setSurname(String surname) {
        this.surname = surname;
    }
}

• Define a class called ‘Person’ with private fields for ID, firstName, and surname

• Then a constructor that allows you to set these fields when creating an instance of the record

• Additionally, provide getter and setter methods for each field to access and modify their values

• To use the record in Java, create an instance of ‘Person’ class and set or retrieve the field values using the provided methods

• For example:

public class Main {
    public static void main(String[] args) {
        Person personRecord = new Person(1, "Tony", "Smith");

        // Accessing the fields of the Person record
        int ID = personRecord.getID();
        String firstName = personRecord.getFirstName();
        String surname = personRecord.getSurname();

        System.out.println("ID: " + ID);
        System.out.println("First Name: " + firstName);
        System.out.println("Surname: " + surname);
    }
}

• This creates an instance of the ‘Person’ record called ‘personRecord’ with an ID of 1, first name “Tony”, and surname “Smith”

• Then uses the getter methods to retrieve the field values and print them to the console

Lists

What is a list?

• A list is a data structure that consists of a number of items where the items can occur more than once

• Lists are similar to 1D arrays and elements can be accessed in the same way

• The difference is that list values are stored non-contiguously

• This means they do not have to be stored next to each other in memory, which is different to how data is stored for arrays

• Lists can also contain elements of more than one data type, unlike arrays

Example in Pseudocode

list pets = ["dog", "cat", "rabbit", "fish"]

Example in Python

pets = ["dog", "cat", "rabbit", "fish"]

Example in Java

import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<String> pets = new ArrayList<>();
        
        // Adding elements to the pets list
        pets.add("dog");
        pets.add("cat");
        pets.add("rabbit");
        pets.add("fish");

        // Printing the elements in the pets list
        for (String pet : pets) {
            System.out.println(pet);
        }
    }
}

Manipulating Lists

There are a range of operations that can be performed involving lists in the table below:

Tuples

What is an Tuple?

• A tuple is an ordered set of values of any type

• It is immutable, this means that it can’t be changed

• Elements, therefore, can’t be added or removed once it has been created

• Tuples are initialised using regular brackets instead of square brackets

• Elements in a tuple are accessed in a similar way to elements in an array, with the exception that values can’t be changed

Example in Pseudocode

tuple1 = (1, 2, 3)

Example in Python

person = ("John", 25, "USA")

print(person)

When should Arrays, Records, Lists & Tuples be used?