Data Structures in Java: Arrays and Lists

Data Structures in Java

Arrays

• A fixed-size, homogeneous collection of elements
• Declared using the [] syntax, e.g. int[] myArray;
• Elements are accessed using an index, e.g. myArray[0]
• Supports various operations, such as:
  • Indexing (getting/setting elements)
  • Length (getting the number of elements)
  • Copying (creating a copy of the array)

Lists

• A dynamic, heterogeneous collection of elements
• Implemented using the java.util.List interface
• Supports various operations, such as:
  • Adding/removing elements
  • Indexing (getting/setting elements)
  • Iterating (traversing the list)
• Common implementations include:
  • ArrayList: a resizable array-based list
  • LinkedList: a linked list implementation

Sets

• An unordered, unique collection of elements
• Implemented using the java.util.Set interface
• Supports various operations, such as:
  • Adding/removing elements
  • Checking for element presence
  • Iterating (traversing the set)
• Common implementations include:
  • HashSet: a hash-based set implementation
  • TreeSet: a sorted set implementation

Maps

• A collection of key-value pairs
• Implemented using the java.util.Map interface
• Supports various operations, such as:
  • Putting/removing entries
  • Getting values by key
  • Iterating (traversing the map)
• Common implementations include:
  • HashMap: a hash-based map implementation
  • TreeMap: a sorted map implementation

Stacks and Queues

• A Last-In-First-Out (LIFO) data structure
• Implemented using the java.util.Stack class
• Supports various operations, such as:
  • Pushing/popping elements
  • Peeking (getting the top element)
• A First-In-First-Out (FIFO) data structure
• Implemented using the java.util.Queue interface
• Supports various operations, such as:
  • Enqueuing/dequeuing elements
  • Peeking (getting the front element)

Trees

• A hierarchical data structure
• Implemented using the java.util.TreeSet and java.util.TreeMap classes
• Supports various operations, such as:
  • Traversing (iterating over the tree)
  • Searching for elements
  • Inserting/removing elements

Arrays

• Fixed-size collection that stores homogenous elements, meaning all elements are of the same type.
• Declared using square brackets syntax, for example, int[] myArray;.
• Access elements via an index, starting from zero, like myArray[0].
• Capable of various operations including:
  • Indexing: Retrieve or modify elements directly by their index.
  • Length: Obtain the number of elements using the .length property.
  • Copying: Create a duplicate array using methods like System.arraycopy().

Lists

• Dynamic collections that can grow or shrink in size and can contain heterogeneous elements.
• Implemented through the java.util.List interface, allowing flexibility in data operations.
• Supports key operations such as:
  • Adding/Removing: Modify the list by inserting or deleting elements.
  • Indexing: Access elements by numerical index similar to arrays.
  • Iterating: Traverse the list using iterators or enhanced for-loops.
• Common implementations include:
  • ArrayList: Allows for resizable arrays, offering fast random access.
  • LinkedList: Utilizes a linked-node structure, optimizing for insertion and removal operations.

Sets

• Unordered collections that store unique elements, preventing duplicates.
• Implemented through the java.util.Set interface for unique element storage.
• Supports operations such as:
  • Adding/Removing: Modify the set contents easily.
  • Checking Presence: Determine if an element exists in the set.
  • Iterating: Navigate through the elements in the set.
• Common implementations include:
  • HashSet: Offers efficient storage and retrieval with hash-based structure.
  • TreeSet: Maintains sorted order of elements using a red-black tree.

Maps

• Collections of key-value pairs allowing for efficient data retrieval by key.
• Implemented through the java.util.Map interface for versatile pairing.
• Supports key operations such as:
  • Putting/Removing Entries: Modify pairs in the map dynamically.
  • Getting Values by Key: Retrieve corresponding values efficiently using keys.
  • Iterating: Navigate through map entries using entry sets.
• Common implementations include:
  • HashMap: Provides fast access and is unordered.
  • TreeMap: Keeps keys sorted based on natural ordering or a comparator.

Stacks and Queues

• Stack: A LIFO (Last-In-First-Out) data structure, where the most recently added element is the first to be removed.
  • Implemented using the java.util.Stack class.
  • Operations include:
    • Pushing/Popping: Add or remove elements at the top of the stack.
    • Peeking: Retrieve the top element without removing it.
• Queue: A FIFO (First-In-First-Out) structure, where the earliest added element is the first to be removed.
  • Implemented through the java.util.Queue interface.
  • Operations include:
    • Enqueuing/Dequeuing: Add or remove elements from the ends of the queue.
    • Peeking: Access the front element without dequeuing.

Trees

• Hierarchical data structures ideal for representing sorted or structured data.
• Implemented using java.util.TreeSet and java.util.TreeMap classes for efficient storage.
• Supports a variety of operations including:
  • Traversing: Iterating over tree elements typically using in-order, pre-order, or post-order methods.
  • Searching: Efficiently locating elements in logarithmic time.
  • Inserting/Removing: Managing the structure of the tree while maintaining its properties.

Understand the basics of arrays and lists in Java, including declaration, indexing, and operations. Learn about the differences between fixed-size homogeneous arrays and dynamic heterogeneous lists.