Java Collection Implementations
1. Introduction
The Java Collections Framework is a unified architecture for representing and manipulating collections. It provides a set of interfaces and classes that allow developers to manage groups of objects efficiently.
2. Key Concepts
2.1 Interfaces
The main interfaces of the Java Collections Framework are:
- Collection
- List
- Set
- Map
2.2 Implementations
Common implementations include:
- ArrayList - A resizable array implementation of the List interface.
- LinkedList - A doubly-linked list implementation of the List interface.
- HashSet - A hash table implementation of the Set interface.
- TreeSet - A red-black tree implementation of the Set interface.
- HashMap - A hash table implementation of the Map interface.
- TreeMap - A red-black tree implementation of the Map interface.
3. Collection Types
3.1 Lists
Lists are ordered collections that allow duplicates. The most commonly used implementations are:
- ArrayList
- LinkedList
3.2 Sets
Sets are collections that do not allow duplicates. Common implementations include:
- HashSet
- LinkedHashSet
- TreeSet
3.3 Maps
Maps are collections that map keys to values. Key characteristics include:
- Each key is unique.
- Values can be duplicated.
4. Best Practices
When using collections in Java, consider the following best practices:
- Choose the right collection type based on your needs.
- Prefer interfaces over implementations for variable declarations.
- Be cautious with null values in collections.
5. FAQ
What is the difference between List and Set?
A List allows duplicate elements and maintains the order of insertion, while a Set does not allow duplicates and does not guarantee any specific order.
Which collection should I use for fast lookups?
Use a HashMap or HashSet for fast lookups as they provide average O(1) time complexity for search operations.
Can I store null values in a HashMap?
Yes, you can store null values, but only one null key is allowed.