Learning Data Structures & Algorithms in Java

Data Structures

• Enumeration
• BitSet
• Vector
• Stack
• Dictionary
• Hashtable
• Properties

Collection Interfaces

• Collections Interface
• List Interface
• Set
• SortedSet
• Map
• Map.Entry
• SortedMap
• Enumeration

Collection Classes

• AbstractCollection
• AbstractList
• AbstractSequentialList
• LinkedList
• ArrayList
• AbstractSet
• HashSet
• LinkedHashSet
• TreeSet
• AbstractMap
• HashMap
• TreeMap
• WeakHashMap
• LinkedHashMap
• IdentityHashMap

Collection Interfaces

Set

Interface Set<E> JavaDoc

Key Info

• A collection that contains no duplicate elements.

Collection Classes

LinkedList

HashMap

HashMap<K, V> extends AbstractMap<K, V> implements Map<K, V> Default Initial Capacity: 16, Load Factor: 0.75. JavaDoc

Key Info

• To access a value, you must know its key.
• Hashing is the technique of converting a large String to a small String that represents the same String. The shorter value helps in indexing and faster searches.
• It internally uses a LinkedList to store Key:Value pairs. It contains an array of Node, a class with four fields (int hash, K key, V value, Node next).
• They don't allow duplicate keys, but do allow duplicate values. They allow null values, but only a single null key. Likewise, multiple null values.
• This class makes no guarantee that it's order will be maintained over time. It is 'unsynchronised', also meaning that multiple threads can access it simultaneously.

Algorithmic Complexity

• Time Complexity: O(1) (Constant Time) for basic operations like get() and put(). Iteration over a HashMap is directly proportional to the capacity + size where the capacity is the number of buckets.
• Performance of a HashMap is dependent on it's Initial Capacity and it's Load Factor.
  • Initial Capacity: The number of buckets in the HashMap upon instantiation.
  • Load Factor: A measure of how full the hash table is allowed to get before it's capacity is automatically rehashed. Good Explanation.