2.1.1 Collection Interfaces Explained

Collection interfaces in Java provide a framework for storing and manipulating groups of objects. Understanding these interfaces is crucial for effectively managing collections of data in Java SE 11.

Key Concepts

1. Collection Interface

The Collection interface is the root interface of the collection hierarchy. It defines the basic operations that all collections should support, such as adding, removing, and querying elements.

Example

        Collection collection = new ArrayList<>();
        collection.add("Apple");
        collection.add("Banana");
        collection.remove("Apple");
        System.out.println(collection); // Output: [Banana]
    

2. List Interface

The List interface extends the Collection interface and represents an ordered collection of elements. It allows duplicate elements and provides methods to access elements by their index.

Example

        List list = new ArrayList<>();
        list.add("Apple");
        list.add("Banana");
        list.add("Cherry");
        System.out.println(list.get(1)); // Output: Banana
    

3. Set Interface

The Set interface also extends the Collection interface and represents a collection of unique elements. It does not allow duplicate elements and does not guarantee any specific order.

Example

        Set set = new HashSet<>();
        set.add("Apple");
        set.add("Banana");
        set.add("Apple"); // Duplicate element, will not be added
        System.out.println(set); // Output: [Apple, Banana]
    

4. Queue Interface

The Queue interface extends the Collection interface and represents a collection designed for holding elements prior to processing. It follows the FIFO (First-In-First-Out) principle.

Example

        Queue queue = new LinkedList<>();
        queue.add("Apple");
        queue.add("Banana");
        System.out.println(queue.poll()); // Output: Apple
    

5. Map Interface

The Map interface is not a true collection, but it maps keys to values. It does not extend the Collection interface but is part of the collection framework. It allows unique keys and can have duplicate values.

Example

        Map map = new HashMap<>();
        map.put("fruit1", "Apple");
        map.put("fruit2", "Banana");
        System.out.println(map.get("fruit1")); // Output: Apple
    

Examples and Analogies

Think of the Collection interface as a general container for objects, similar to a box that can hold various items. The List interface is like a numbered list where each item has a specific position.

The Set interface is like a bag that can only hold one of each type of item, ensuring no duplicates. The Queue interface is like a line at a store, where the first person in line is the first to be served.

The Map interface is like a dictionary, where each word (key) has a definition (value) associated with it. By mastering these collection interfaces, you can efficiently manage and manipulate collections of data in your Java SE 11 applications.