2. Collection hierarchy in java ( Part 1: Interfaces ) How2Do

Collection hierarchy in java.

Collection hierarchy in java refers to the relationship between different classes and interfaces in a collection framework. The Java Collections Framework provides a set of interfaces and classes that define various types of collections and their behaviors. The collection hierarchy in Java is based on a few key interfaces and their respective implementing classes.

At the top of the hierarchy is the Collection interface, which represents a group of objects. This interface provides basic operations for manipulating and querying collections, such as adding, removing, and checking the presence of elements. The Collection interface is extended by two main sub interfaces: List and Set.

Interfaces Of Collection In java:

1. Iterable Interface :

The Iterable interface in Java is a fundamental interface in the Java Collections Framework. It serves as the foundation for classes that represent a group of elements and enables them to be iterated over using an enhanced for loop or through the use of iterators.

Here are some key characteristics and features of the Iterable interface:

Iteration Capability: The primary purpose of the Iterable interface is to provide the ability to iterate over a collection of elements. It achieves this by defining a single method, iterator(), which returns an Iterator object.
Enhanced for Loop Support: By implementing the Iterable interface, a class enables the use of the enhanced for loop, also known as the for-each loop, which simplifies the process of iterating over elements in a collection.
Iterator Support: The iterator() method of the Iterable interface returns an Iterator object, which allows sequential access to the elements in the collection. The Iterator provides methods such as hasNext(), next(), and remove(), which facilitate iteration and element manipulation.
Multiple Iterations: The Iterable interface allows multiple iterations over the elements of a collection. Each call to iterator() returns a new Iterator, allowing independent traversal of the elements.
Usage with Custom Classes: Implementing the Iterable interface is useful when creating custom classes that represent collections of objects. By doing so, instances of those classes can be used with the enhanced for loop and other APIs that accept Iterable objects.
Integration with Java APIs: Many core Java classes and APIs, such as the Java Collections Framework, rely on the Iterable interface. This enables seamless integration and compatibility with various Java libraries and utilities.

By implementing the Iterable interface, classes gain the ability to provide a way for their elements to be iterated over, making them compatible with enhanced for loops and other iteration-based operations in Java. It facilitates a standardized approach to working with collections, enhancing code readability and promoting code reusability.

2. Collection Interface :

The Iterable interface of Collection hierarchy in java is a fundamental interface in the Java Collections Framework. It serves as the foundation for classes that represent a group of elements and enables them to be iterated over using an enhanced for loop or through the use of iterators.

Here are some key characteristics and features of the Iterable interface:

Iteration Capability: The primary purpose of the Iterable interface is to provide the ability to iterate over a collection of elements. It achieves this by defining a single method, iterator(), which returns an Iterator object.
Enhanced for Loop Support: By implementing the Iterable interface, a class enables the use of the enhanced for loop, also known as the for-each loop, which simplifies the process of iterating over elements in a collection.
Iterator Support: The iterator() method of the Iterable interface returns an Iterator object, which allows sequential access to the elements in the collection. The Iterator provides methods such as hasNext(), next(), and remove(), which facilitate iteration and element manipulation.
Multiple Iterations: The Iterable interface allows multiple iterations over the elements of a collection. Each call to iterator() returns a new Iterator, allowing independent traversal of the elements.
Usage with Custom Classes: Implementing the Iterable interface is useful when creating custom classes that represent collections of objects. By doing so, instances of those classes can be used with the enhanced for loop and other APIs that accept Iterable objects.
Integration with Java APIs: Many core Java classes and APIs, such as the Java Collections Framework, rely on the Iterable interface. This enables seamless integration and compatibility with various Java libraries and utilities.

3. List Interface :

The List interface of Collection hierarchy in java is a part of the Java Collections Framework and provides an ordered collection of elements that allows duplicates. It is designed to represent a sequence of objects in which each element has an index associated with it.

Here are some key characteristics and features of the List interface:

Ordered Collection: Elements in a List are ordered based on their index position, which means they maintain the insertion order. The first element is at index 0, the second element at index 1, and so on.
Duplicates Allowed: Unlike some other collection types, List allows duplicate elements. This means you can store multiple elements with the same value in a List.
Access by Index: List provides methods to access elements based on their index. You can retrieve an element by its index using the get(int index) method.
Dynamic Size: Lists in Java automatically resize themselves to accommodate new elements. You can add elements to a List using the add(E element) method, which appends the element to the end of the List.
Modifiable: List allows you to modify elements by their index. You can change the value of an element at a specific index using the set(int index, E element) method.
Iteration: Lists can be easily iterated over using the enhanced for loop or by utilizing an Iterator or ListIterator. These iterators provide methods for traversing and manipulating the elements of a List.
Implementations: Java provides several classes that implement the List interface, such as ArrayList, LinkedList, and Vector. Each implementation has its own characteristics in terms of performance, memory usage, and specific use cases.

The List interface provides a flexible and powerful way to work with ordered collections of elements in Java, allowing you to perform various operations such as adding, removing, searching, and sorting elements based on their index.

4. Queue Interface :

The Queue interface of Collection hierarchy in java is a part of the Java Collections Framework and represents a collection that orders elements in a specific manner for processing. It follows the First-In-First-Out (FIFO) principle, where elements are added at the end of the queue and removed from the front.

Here are some key characteristics and features of the Queue interface:

Ordering: The Queue interface maintains the order of elements based on the FIFO principle. The element that has been in the queue the longest is the first one to be removed.
Addition and Removal: Elements are added to the end of the queue using the add(E element) or offer(E element) method. To remove an element from the front of the queue, you can use the remove() or poll() method. These methods also return the removed element.
Retrieval: The Queue interface provides methods to retrieve the element at the front of the queue without removing it. The peek() method returns the element, or null if the queue is empty. The element() method is similar to peek() but throws an exception if the queue is empty.
Size and Empty Check: The size() method returns the number of elements in the queue, while the isEmpty() method checks if the queue is empty.
Implementation Choices: Java offers various classes that implement the Queue interface, such as LinkedList, PriorityQueue, and ArrayDeque. Each implementation has its own characteristics and performance trade-offs.
Blocking Queues: Java also provides specialized implementations of the Queue interface called BlockingQueue. These implementations support thread-safety and blocking operations, allowing threads to wait until the queue becomes non-empty or non-full.
Iteration: The Queue interface does not provide direct iteration over its elements. To iterate through the elements, you can convert the Queue to an array or use an Iterator or ListIterator provided by the specific implementation class.

The Queue interface is useful in scenarios where you need to process elements based on their arrival order. It is commonly used in tasks such as event handling, task scheduling, and implementing algorithms like breadth-first search. By following the FIFO principle, the Queue interface provides a simple and efficient way to manage and process elements in a specific order.

5. Set Interface :

The Set interface of Collection hierarchy in java is a part of the Java Collections Framework and represents a collection of unique elements, where duplicates are not allowed. It provides a mathematical set abstraction and offers various methods for adding, removing, and manipulating elements.

Here are some key characteristics and features of the Set interface:

Uniqueness of Elements: The Set interface ensures that each element in the collection is unique. It does not allow duplicates, meaning that if you attempt to add an element that is already present, it will not be added again.
No Defined Ordering: Unlike some other collection types, such as List, Set does not guarantee a specific order of elements. The elements are stored in an internal structure that optimizes for efficient membership operations.
Add and Remove Operations: Elements can be added to a Set using the add(E element) method. If the element is successfully added, the method returns true; otherwise, if the element already exists, it returns false. The remove(Object element) method removes a specific element from the Set.
Membership Testing: The Set interface provides methods to test if a given element is present in the Set. The contains(Object element) method returns true if the Set contains the specified element; otherwise, it returns false. The isEmpty() method checks if the Set is empty.
Set Operations: The Set interface supports various set operations, such as union, intersection, and difference. For example, you can perform these operations between two sets using methods like addAll(Collection<? extends E> c), retainAll(Collection<?> c), and removeAll(Collection<?> c).
Iteration: The elements of a Set can be iterated over using an enhanced for loop or by utilizing an Iterator. The Set interface provides the iterator() method, which returns an Iterator object for traversing the elements.
Implementation Choices: Java provides several classes that implement the Set interface, such as HashSet, TreeSet, and LinkedHashSet. Each implementation has its own characteristics in terms of performance, ordering, and specific use cases.

The Set interface in Java is a powerful tool for managing collections of unique elements. It ensures that each element appears only once within the Set and provides methods for adding, removing, and testing membership. The lack of a defined order makes Sets ideal for scenarios where uniqueness is a priority, and the efficient lookup of elements is required.

6. Deque Interface :

The Deque interface of Collection hierarchy in java is a part of the Java Collections Framework and represents a double-ended queue, which allows insertion and removal of elements from both ends. “Deque” stands for “double-ended queue.”

Here are some key characteristics and features of the Deque interface:

Double-Ended Operations: The Deque interface supports operations to insert and remove elements from both the front and the back of the queue. This flexibility allows for efficient insertion and removal at both ends.
Queue and Stack Functionality: The Deque interface provides methods to add elements to the end of the deque (addLast(E e) or offerLast(E e)) and retrieve and remove elements from the front of the deque (removeFirst() or pollFirst()). These methods enable the Deque to function as both a queue and a stack.
Stack-Like Operations: The Deque interface also supports stack-like operations, such as pushing elements to the front of the deque (addFirst(E e) or offerFirst(E e)) and popping elements from the front of the deque (removeFirst() or pollFirst()). These methods allow the Deque to be used as a stack, following the Last-In-First-Out (LIFO) principle.
Random Access: The Deque interface provides methods to access elements at specific positions within the deque, such as getFirst() and getLast(), which return the first and last elements, respectively.
Size and Empty Check: The size() method returns the number of elements in the deque, while the isEmpty() method checks if the deque is empty.
Iteration: The Deque interface allows iteration over its elements using an enhanced for loop or by utilizing an Iterator or ListIterator. These iterators provide methods for traversing and manipulating the elements of the deque.
Implementation Choices: Java provides several classes that implement the Deque interface, such as ArrayDeque and LinkedList. Each implementation has its own characteristics in terms of performance, memory usage, and specific use cases.

The Deque interface offers a flexible and efficient way to manage and manipulate collections of elements, allowing for insertion and removal at both ends. Its versatility enables it to be used as both a queue and a stack, making it suitable for various scenarios where elements need to be accessed from either end.

7. SortedSet Interface :

The SortedSet interface of Collection hierarchy in java is a subinterface of the Set interface, which extends it to provide a sorted collection of unique elements. It maintains the elements in a sorted order according to their natural ordering or a custom comparator.

Here are some key characteristics and features of the SortedSet interface:

Ordering of Elements: The SortedSet interface guarantees that the elements are stored in a sorted order. The exact order is determined by either the natural ordering of the elements (if they implement the Comparable interface) or a custom comparator provided during the SortedSet instantiation.
Unique Elements: Like the Set interface, the SortedSet interface does not allow duplicate elements. Each element in the SortedSet must be unique according to the comparison logic defined by the natural ordering or the custom comparator.
Sorted Operations: The SortedSet interface provides additional methods specifically related to sorted operations. For example, methods like first() and last() return the first and last elements in the sorted set, respectively. Methods like headSet(E toElement) and tailSet(E fromElement) return views of the sorted set that are restricted to elements less than or equal to the specified element or greater than or equal to the specified element, respectively.
Range Operations: The SortedSet interface allows performing range-based operations on the sorted set. Methods like subSet(E fromElement, E toElement) and subSet(E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) return views of the sorted set that include elements within the specified range. The inclusiveness of the range boundaries can be controlled through the method parameters.
Comparator Control: The SortedSet interface provides methods like comparator() and subSet() to obtain and modify the comparator used for ordering the elements. If the natural ordering is used, the comparator() method returns null.
Implementation Choices: Java provides several classes that implement the SortedSet interface, such as TreeSet and ConcurrentSkipListSet. Each implementation has its own characteristics in terms of performance, concurrency support, and specific use cases.

The SortedSet interface in Java offers a powerful way to work with collections of elements in a sorted manner. It provides a range of methods for accessing, manipulating, and iterating over the sorted set. By enforcing a sorted order, the SortedSet interface allows for efficient search, retrieval, and range-based operations on the elements.

8. Map Interface :

The Map interface of Collection hierarchy in java is a part of the Java Collections Framework and represents a collection of key-value pairs, where each key is unique. It allows for efficient lookup and retrieval of values based on their associated keys.

Here are some key characteristics and features of the Map interface:

Key-Value Pairs: The Map interface represents a collection of key-value pairs, where each key is associated with a corresponding value. Both keys and values can be of any object type.
Unique Keys: The keys in a Map must be unique. If an attempt is made to add a duplicate key, it will replace the existing key-value pair with the new one.
Efficient Lookup: The primary purpose of a Map is to provide efficient lookup and retrieval of values based on their associated keys. You can retrieve the value associated with a key using the get(Object key) method.
Key-Value Manipulation: The Map interface provides methods to add, remove, and modify key-value pairs. The put(K key, V value) method adds a key-value pair to the Map, remove(Object key) removes a specific key-value pair, and replace(K key, V value) modifies the value associated with a given key.
Iteration: The elements of a Map can be iterated over using methods like keySet(), values(), and entrySet(). The keySet() method returns a Set containing all the keys in the Map, values() returns a Collection containing all the values, and entrySet() returns a Set containing all the key-value pairs as Map.Entry objects.
Implementation Choices: Java provides several classes that implement the Map interface, such as HashMap, TreeMap, and LinkedHashMap. Each implementation has its own characteristics in terms of performance, ordering, memory usage, and specific use cases.
Null Keys and Values: Most Map implementations allow null values, and some also allow null keys (such as HashMap and LinkedHashMap). However, TreeMap does not allow null keys.

The Map interface in Java provides a powerful way to store, access, and manipulate key-value pairs. It is widely used in various applications and algorithms where efficient data retrieval based on keys is crucial. By enforcing unique keys and providing efficient lookup methods, the Map interface enables developers to work with associative data structures efficiently.

9. SortedMap Interface :

The SortedMap interface of Collection hierarchy in java is a subinterface of the Map interface, which extends it to provide a sorted collection of key-value pairs. It maintains the elements in a sorted order based on the natural ordering of the keys or a custom comparator.

Here are some key characteristics and features of the SortedMap interface:

Ordering of Keys: The SortedMap interface guarantees that the keys are stored in a sorted order. The exact order is determined by either the natural ordering of the keys (if they implement the Comparable interface) or a custom comparator provided during the SortedMap instantiation.
Unique Keys: Like the Map interface, the SortedMap interface does not allow duplicate keys. Each key in the SortedMap must be unique according to the comparison logic defined by the natural ordering or the custom comparator.
Sorted Operations: The SortedMap interface provides additional methods specifically related to sorted operations. For example, methods like firstKey() and lastKey() return the first and last keys in the sorted map, respectively. Methods like headMap(K toKey) and tailMap(K fromKey) return views of the sorted map that are restricted to keys less than or equal to the specified key or greater than or equal to the specified key, respectively.
Range Operations: The SortedMap interface allows performing range-based operations on the sorted map. Methods like subMap(K fromKey, K toKey) and subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) return views of the sorted map that include key-value pairs within the specified range. The inclusiveness of the range boundaries can be controlled through the method parameters.
Comparator Control: The SortedMap interface provides methods like comparator() and subMap() to obtain and modify the comparator used for ordering the keys. If the natural ordering is used, the comparator() method returns null.
Implementation Choices: Java provides several classes that implement the SortedMap interface, such as TreeMap and ConcurrentSkipListMap. Each implementation has its own characteristics in terms of performance, concurrency support, memory usage, and specific use cases.

The SortedMap interface in Java offers a powerful way to work with key-value pairs in a sorted manner. It provides a range of methods for accessing, manipulating, and iterating over the sorted map. By enforcing a sorted order based on the keys, the SortedMap interface allows for efficient search, retrieval, and range-based operations on the key-value pairs.