How many types of interfaces are there in Java?

Carol 115 Published: 12/23/2024

How many types of interfaces are there in Java?

I'd be happy to help!

In the world of Java programming, interfaces play a crucial role in defining the behavior and structure of an object-oriented program. An interface is a abstract construct that defines a contract or a protocol for its implementations. It's like a blueprint or a set of instructions on how to behave.

Now, let's talk about the different types of interfaces in Java! There are several types, but I'll cover at least 10:

Functional Interface: A functional interface is an interface that has exactly one abstract method (SAM). These interfaces can be used as lambda expressions or method references. Think of them like a mini-program within your program.

Example: java.util.function.Predicate<T> is a functional interface that takes in an input and returns a boolean value indicating whether the input meets certain criteria.

Marker Interface: A marker interface is simply an empty interface with no methods or fields. Its sole purpose is to identify objects that implement this interface, usually for some specific functionality or attribute.

Example: java.lang.Cloneable is a marker interface used to indicate that an object can be cloned.

Pure Virtual Interface (PVI): A PVI is an interface with no concrete methods and only abstract methods. It provides a blueprint for other interfaces or classes to follow.

Example: java.awt.print.PrinterJob has no concrete methods, but it's a PVI because its implementations must provide their own logic.

Concrete Interface: A concrete interface is one that has at least one concrete method (i.e., not abstract). These interfaces can be implemented directly or extended by other interfaces or classes.

Example: java.lang.Runnable has a single concrete method run(), which is meant to be overridden by its implementations.

Abstract Interface: An abstract interface is an interface with only abstract methods, meaning they must be implemented by any class that implements the interface.

Example: java.awt.print.Pageable has several abstract methods related to printing pages.

Composite Interface: A composite interface combines multiple interfaces into a new interface, allowing for easier reuse and inheritance.

Example: java.sql.Statement is an interface that inherits from both java.sql.PreparedStatement and java.sql.ResultSet.

Tagged Interface: A tagged interface is one where you can use Java's annotation system to attach metadata or tags to the interface itself or its methods.

Example: javax.persistence.Entity is a tagged interface used in JPA (Java Persistence API) to identify an entity bean.

Parameterized Interface: A parameterized interface is one that takes one or more type parameters, similar to Java generics.

Example: java.util.Map<K, V> is a parameterized interface for maps, where K represents the key type and V represents the value type.

Multicast Interface: A multicast interface allows multiple classes to implement the same method signature with different implementations.

Example: java.awt.event.MouseListener has several methods (like mouseClicked()) that can be implemented differently by various mouse listener classes.

Extension Interface: An extension interface is one that provides default or template code for its implementations, which can then customize it as needed.

Example: javax.swing.table.TableModel has abstract methods and some implementation-specific logic, allowing custom models to inherit from this interface.

These are just a few of the many types of interfaces in Java. Understanding each type's unique characteristics will help you write more effective and reusable code.

What are the interfaces in collection in Java?

I'd be happy to help you with that!

In Java, an interface is a abstract class that is designed purely to provide a contract or a blueprint for other classes to implement its methods and variables. Interfaces are used to define a common protocol that multiple classes can adhere to.

There are several interfaces in the collection framework of Java, which are used to provide additional functionality beyond the basic operations provided by the core interfaces like List, Set, and Map.

Here's a list of some key interfaces in the collection framework:

Iterable: This interface is used to create an object that can be iterated over. It provides a method called iterator(), which returns an iterator for the object. ListIterator: This interface extends Iterator and provides additional methods to navigate a list, such as previous() and nextIndex(). Collection: This is one of the most fundamental interfaces in Java's collection framework. It defines methods like add(), contains(), and size(). All collections (like List, Set, etc.) must implement this interface. List: This interface extends Collection and provides a way to access elements by their index. It includes methods like get(index), set(index, element) and add(index, element). Set: Similar to the List interface, but allows for duplicate elements only if they are equal using the equals() method from the Object class. Map: This interface is used to represent a collection of key-value pairs. It includes methods like put(key, value), get(key) and remove(key). SortedMap and SortedSet: These interfaces extend their unsorted counterparts (Map and Set) but also require the elements to be sorted according to some natural ordering or a Comparator provided by the programmer. Queue: This interface defines a first-in, first-out (FIFO) collection of objects that provides methods like offer() and peek() for adding and removing elements. Deque: This interface extends Queue and adds additional operations for inserting and removing elements at arbitrary positions in the queue using addFirst(), removeFirst(), addLast(), and removeLast(). Comparator: This interface defines a way to compare two objects based on some criteria, often used when sorting or searching collections of objects.

These interfaces provide a way for developers to work with collections in Java, ensuring that they are designed with certain requirements or constraints in mind. They also allow for code reuse and polymorphism by providing a standardized way of working with different types of data structures.