Collections

Collections in Java refer to a group of objects or elements that are stored in a structured and organized way. The collections framework in Java provides a set of interfaces and classes to handle different types of collections.

Some of the commonly used interfaces in the collections framework are:

List: An ordered collection of elements that allows duplicate entries.

Set: An unordered collection of unique elements.

Map: A collection that stores key-value pairs.

The collections framework provides several classes that implement these interfaces. For example:

ArrayList: Implements the List interface using an array to store elements.

LinkedList: Implements the List interface using a linked list to store elements.

HashSet: Implements the Set interface using a hash table to store elements.

TreeMap: Implements the Map interface using a red-black tree to store key-value pairs.

Java also provides a class called Collections that contains various methods to manipulate collections. Some of the commonly used methods are:

sort(): Sorts the elements in a collection.

reverse(): Reverses the order of elements in a collection.

shuffle(): Randomly shuffles the elements in a collection. Strings and StringBuffer are also important classes in Java. Strings are immutable, meaning their values cannot be changed after they are created. StringBuffer, on the other hand, is mutable and allows for the modification of its contents. StringBuffer is typically used when there is a need to concatenate or manipulate strings frequently, as it is more efficient than creating multiple string objects.