D.4.8 Standard Library Collections Notes

Java Default Collections and LinkedList

Java Default Collections

Java provides a rich Collections Framework in the java.util package, offering pre-built and well-optimised data structures such as:

• List (implementations ArrayList, LinkedList, Vector)
• Set (implementations HashSet, TreeSet, LinkedHashSet)
• Queue/Deque (implementations, ArrayDeque, LinkedList

These collections are designed to handle common programming needs without requiring developers to manually implement data structures.

Advantages of Java Default Collections Library Usage

Efficiency

1. Optimised Performance: Library collections are implemented by experts and are optimised for speed and memory usage.
2. Time-Saving: Developers can use these collections without having to write and debug their own implementations.

Reliability

1. Well-Tested: Library collections are thoroughly tested and used by millions of developers, reducing the likelihood of bugs.
2. Consistency: They provide consistent behaviour across different projects and platforms.

Flexibility:

The Library offers multiple implementations of the same data structure, allowing developers to select the one that best suits their needs.

Initialisation of Java Collections

When you create a Java collection such as a LinkedList, you must specify the type of elements it will hold using generics:

LinkedList<String> fruits = new LinkedList<>();   // stores Strings
LinkedList<Integer> numbers = new LinkedList<>(); // stores Integers

1. The type inside < > defines the kind of elements that can be added to the collection.
2. You cannot directly use primitive types (like int, double, char) in generics.

Hence, we need Java Wrapper Classes that convert primitive data types into objects, allowing them to be stored in collections.

LinkedList<Integer> numbers = new LinkedList<>();
numbers.add(5); // you can still use primitive as wrapper object due to **autoboxing**

Common Operations of LinkedList

The standard library provides methods to perform common operations on LinkedLists.

import java.util.LinkedList;

public class Main {
    public static void main(String[] args) {
        
        // initialisation
        LinkedList<String> fruits = new LinkedList<>();

        // add elements
        fruits.add("Apple"); // add at the end
        fruits.add("Orange");
        fruits.add(1, "Banana"); // insert at index 1

        System.out.println("After adding: " + fruits);

        // removing elements
        fruits.remove("Orange"); // remove by value
        fruits.remove(0); // remove by index

        System.out.println("After removing: " + fruits);

        // add more elements
        fruits.add("Orange");
        fruits.add("Grapes");
        System.out.println("After adding again: " + fruits);
        // testing accessing and modifying
        String secondFruit = fruits.get(1); // get element at index
        System.out.println("Element at index 1: " + secondFruit);

        fruits.set(1, "Pineapple"); // replace element at index
        System.out.println("After replacing: " + fruits);

        // Checking size and emptiness
        int size = fruits.size(); // number of elements
        System.out.println("Size: " + size);

        boolean empty = fruits.isEmpty(); // check if empty
        System.out.println("Emptiness: " + empty);
    }
}