Collection Framework

The java.util package contains numerous data structure classes for handling data. These data structure classes are collectively known as the Collection Framework.

Data Structures #

• A data structure is a structure that can store data.
• For example, just as you use a bookshelf to store books, you need methods to manage various types of data in different ways. Data structures and the Collection Framework provide these methods.

Collection Framework #

• The most fundamental interface in the Collection Framework is the Collection interface.
  • The Collection interface signifies the presence of data.
  • The Collection interface allows duplicates and does not remember the order in which data was stored.
  • Key methods of the Collection interface include add(), size(), and iterator().
  • Since Collection does not remember the storage order, it cannot provide functionalities like "give me the first element" or "give me the second element."
  • Collection returns an Iterator interface, which allows retrieving stored data one by one.
    • The Iterator has a hasNext() method to check if there are more elements to retrieve and a next() method to retrieve an element.

Set Data Structure #

• An interface representing a data structure that does not allow duplicates.
  • It inherits from the Collection interface.
  • The add method of the Set interface returns false if the element already exists and true if it's a new element.

List Data Structure #

• Represents a data structure that allows duplicates and remembers the order.
  • Similar to the Set interface, it inherits from the Collection interface.
  • Since List remembers the order, it has a get method to retrieve the n-th element.

Map Data Structure #

• It is a data structure that holds Key-Value pairs.
  • When storing data, it uses the put(key, value) method to store key-value pairs together.
  • To retrieve a desired value, it uses the get() method, which takes the key as a parameter.
  • All Keys stored in a Map must not have duplicate values.
  • Due to this characteristic of Keys, Map has a keySet() method that returns a Set containing information about all its Keys.

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