For working professionals
For fresh graduates
More
6. JDK in Java
7. C++ Vs Java
16. Java If-else
18. Loops in Java
20. For Loop in Java
45. Packages in Java
52. Java Collection
55. Generics In Java
56. Java Interfaces
59. Streams in Java
62. Thread in Java
66. Deadlock in Java
73. Applet in Java
74. Java Swing
75. Java Frameworks
77. JUnit Testing
80. Jar file in Java
81. Java Clean Code
85. Java 8 features
86. String in Java
92. HashMap in Java
97. Enum in Java
100. Hashcode in Java
104. Linked List in Java
108. Array Length in Java
110. Split in java
111. Map In Java
114. HashSet in Java
117. DateFormat in Java
120. Java List Size
121. Java APIs
127. Identifiers in Java
129. Set in Java
131. Try Catch in Java
132. Bubble Sort in Java
134. Queue in Java
141. Jagged Array in Java
143. Java String Format
144. Replace in Java
145. charAt() in Java
146. CompareTo in Java
150. parseInt in Java
152. Abstraction in Java
153. String Input in Java
155. instanceof in Java
156. Math Floor in Java
157. Selection Sort Java
158. int to char in Java
163. Deque in Java
171. Trim in Java
172. RxJava
173. Recursion in Java
174. HashSet Java
176. Square Root in Java
189. Javafx
Java, one of the most widely used programming languages, offers various features enabling developers to write robust and flexible code. One such attribute is interfaces. Java interfaces play a crucial role in achieving flexibility and extensibility in software development. This blog post will explore their concept, understand their purpose, and delve into their syntax and implementing interface in java examples. So, let's demystify Java interfaces and discover how they can enhance your programming skills.
Java Interfaces provide a way to define a contract that classes must adhere to. They are a set of methods that a class implementing the interface must exhibit. By using interfaces, you can achieve total abstraction, multiple inheritance, and loose coupling in your code. They serve as a blueprint for classes and allow you to create program instructions that are more modular, reusable, and easily maintainable.
In Java, an interface is a collection of abstract methods, constants, and nested types. It defines a contract that specifies what methods a class implementing an interface must have. An interface declaration is similar to a class declaration but uses the interface keyword instead of the class keyword.
Generally, an interface can be thought of as a repository for the method signatures that will be used to implement in the code section. The degrees of abstraction get raised.
After a brief introduction to Java's interfaces, we will now discuss their necessity and advantages over the traditional use of abstract classes.
There are different types of Interfaces in Java that are used for various purposes. Their uses are listed below.
1. Achieving Abstraction: Interfaces allow you to achieve total abstraction, where you define a contract without specifying the implementation details. This enables you to separate the interface from the implementation, making your code more modular and maintainable.
2. Java Interfaces Can Have Multiple Inheritance: Java classes can only inherit from a single superclass, but interfaces can implement multiple interfaces. This allows you to receive behavior from multiple sources, enhancing code reusability and flexibility.
3. Achieving Loose Coupling: Interfaces facilitate loose coupling between components of your code. By depending on them rather than concrete classes, you can easily swap implementations without affecting the clients that use those interfaces.
4. Creating Contracts: Interfaces provide a way to define contracts that classes must adhere to. By using these, you can ensure that classes implementing the interface provide specific functionality, making your code more reliable and predictable.
Class | Interface | |
Instantiation | Can be instantiated using the ‘new’ keyword | It cannot be instantiated |
Inheritance | Supports single inheritance | Supports multiple inheritance |
Abstract Methods | Can have abstract and non-abstract methods | Can only have abstract methods |
Constructors | Can have constructors | Cannot have constructors |
Java Interface Variables | Can have instance variables | Can have only constants (static final variables) |
Method Implementation | Can provide method implementations | Can only declare method signatures (no implementation) |
Access Modifiers | Can have different access modifiers | Methods are implicitly public |
Type of Relationship | Represents a blueprint or implementation of behavior | Represents a contract that classes must adhere to |
Object Creation | Can create objects of the class | It cannot create objects directly but can be implemented by classes to create objects |
Extensibility | Can extend other classes | Can extend other interfaces |
Interface Implementations | Classes can implement multiple interfaces | Interfaces can extend multiple interfaces |
Total abstraction refers to the concept of hiding implementation details and only exposing the essential functionality or behavior to the user. In Java, interfaces provide a way to achieve total abstraction. Let's understand this with an example:
Let's create a class called Rectangle that implements the Shape interface:
In this example, the Rectangle class implements the Shape interface, achieving total abstraction by hiding the internal details about area and perimeter calculations, allowing users to interact through the interface.
Multiple inheritance refers to the ability of a class to inherit characteristics and behaviors from more than one parent class. In Java, a class can take over from only one superclass but can implement multiple interfaces, allowing for different inheritances.
See the example below:
In this example, the Bird class implements both the Flyable and Swimmable interfaces, allowing it to inherit the behavior defined in both. The Bird class provides its own implementation for the fly() and swim() methods.
By using interfaces, Java allows for achieving a form of multiple inheritance. A class can implement many interfaces, enabling it to inherit and execute desired behaviors from different sources.
Loose coupling is a design principle that promotes a modular and flexible software architecture, where components or modules are independent of each other and interact through well-defined interfaces. Java interfaces play a crucial role in achieving this.
Consider a scenario where you have two classes: OrderProcessor and PaymentGateway. The former class needs to communicate with the latter to process payments. By using interfaces, you can achieve loose coupling between OrderProcessor and PaymentGateway.
Let's see how this can be implemented:
In this example, the PaymentGateway interface defines the contract for processing payments. The OrderProcessor class has a dependency on this through its constructor. This allows for loose coupling, as the OrderProcessor class doesn't need to know the specific implementation of the payment gateway. It can interact with any class that executes the PaymentGateway interface, providing flexibility and modularity.
The use of interfaces decouples the OrderProcessor class from the concrete implementation of the payment gateway, making the code more maintainable, extensible, and testable.
Use the ‘interface’ keyword to declare an interface. It is employed to offer complete abstraction. By default, all fields in an interface are public, static, and final, and all the methods are declared with an empty body. All of the methods declared must be implemented by a class that executes the interface. Use the keyword ‘implements’ to apply an interface. The following syntax is an example of a Java interface.
Interfaces may be declared as members of another abstract type or class. An interface of this type is referred to as a member interface or nested interface. When declared outside of any other class, an interface in a class can only have the public and default access specifiers.
This class-declared interface has four possible states: default, public, protected, or private. We refer to the interface as c_name when implementing it.i_name, where i_name is the name of the interface itself and c_name is the name of the class in which it is nested.
Using interfaces in Java offers several advantages:
While interfaces provide numerous benefits, there are a few considerations to keep in mind:
1. The default methods: With the release of JDK 8, Java interfaces gained additional features that enhanced their capabilities. The most notable characteristic is the introduction of default methods, which allow interfaces to provide method implementations. Here's an example:
Output:
2. Static Methods: Static methods in interfaces can be invoked independently without an object, another capability added in JDK 8.
Output:
An interface can also extend another interface, enabling the creation of hierarchical relationships. When one extends the other, it inherits the methods and constants from the parent interface. Here's an example:
Output:
When implementing an interface in Java, write it as implementation classes because the interface contains numerous abstract methods. If the implementation is unable to implement all abstract methods, designate the implementation class as abstract and finish implementing the remaining methods in the subsequent child classes that are formed. Multiple child classes may be declared, but at the very end, all abstract methods have been fully implemented.
When using Java interfaces, following certain best practices to ensure clean, maintainable, and effective code is important. Some are listed below.
Java interfaces enable modularity, reusability, and loose coupling by providing a contract that classes must adhere to. Understanding how to use the interfaces effectively can enhance your programming skills and help you build more robust and maintainable Java applications. So embrace their power and add great potential to your Java code.
1. How can I implement multiple interfaces in a Java class?
Answer: To implement multiple interfaces, separate them with commas in the class declaration and provide the required method implementations for each interface.
2. How can interfaces help achieve abstraction in Java?
Answer: Interfaces define a contract that classes must adhere to, allowing for abstraction by separating the interface from the implementation details. This promotes loose coupling and modularity.
3. How can interfaces support polymorphism in Java?
Answer: Interfaces enable polymorphism by allowing objects of different classes to be treated as instances of a common interface. This allows for flexible and interchangeable usage of objects based on their shared behaviors defined by the interface.
Take the Free Quiz on Java
Answer quick questions and assess your Java knowledge
Author
Talk to our experts. We are available 7 days a week, 9 AM to 12 AM (midnight)
Indian Nationals
1800 210 2020
Foreign Nationals
+918045604032
1.The above statistics depend on various factors and individual results may vary. Past performance is no guarantee of future results.
2.The student assumes full responsibility for all expenses associated with visas, travel, & related costs. upGrad does not provide any a.