Lecture on HashSet Collection in Java

Key Concepts

• Collections in Java

  • Collection is a root interface.
  • It is extended into multiple child interfaces: List, Set, and Queue.

• Child Interfaces

  • List Interface: Implemented by ArrayList and LinkedList.
  • Set Interface: Focus of today’s lecture.

Set Interface

• Set Interface Overview

  • Child interface of Collection.
  • Implemented by HashSet and LinkedHashSet.

• Characteristics of Set Interface

  • Duplicates are not allowed.
  • Insertion order is not preserved.

HashSet

• HashSet Class

  • A key class implementing Set interface.
  • Does not allow duplicate elements.
  • Does not maintain insertion order (elements stored in a random order).
  • Uses hashCode for element storage, enhancing search speed.

• Key Features of HashSet

  • No duplicates.
  • No insertion order.
  • Unordered (no index concept).
  • Supports heterogeneous data and allows null values.
  • Efficient for search operations.

Creating HashSet Objects

• Default Creation

  HashSet hs = new HashSet();
  // Default initial size: 16, Load factor: 0.75
  

• Custom Initial Size and Load Factor

  HashSet hs = new HashSet(100);
  HashSet hs = new HashSet(100, 0.90f);
  

  • Initial size specifies storage capacity.
  • Load factor (fill ratio) determines when to increase object size (default 0.75).

• Type Restriction

  HashSet<Integer> hs = new HashSet<>();
  // Stores only Integer objects
  

HashSet Operations

• Adding Elements

  hs.add(value);
  hs.addAll(collection);
  

• Removing Elements

  hs.remove(value);
  hs.removeAll(collection);
  

• Checking Elements

  hs.contains(value);
  hs.containsAll(collection);
  hs.isEmpty();
  

• Iteration

  • Using enhanced for loop or iterator.

  for (Object obj : hs) { ... }
  
  Iterator it = hs.iterator();
  while (it.hasNext()) { ... }
  

Limitations and Considerations

• Sorting and Shuffling
  • Not directly possible; requires conversion to ArrayList.

Set Operations

• Union, Intersection, Difference

  • Use methods like addAll(), retainAll(), removeAll() to perform set operations.

• Subset Checking

  hs.containsAll(otherSet);
  

Conclusion

• HashSet is valuable for scenarios needing fast search and no duplicates.
• Understand capabilities and limits, like lack of direct sorting.