Image: Interface in JAVA
Image: Interface in JAVA

As complex as it may be to wrap your head around this concept, this article will unravel the world of Interfaces in Java for you with practical examples.

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An interface is a set of methods that you would want your class to implement. These methods are public and abstract by default(you don’t have to explicitly use the “abstract” keyword), and any class implementing your interface will need to provide implementations of those methods.

The intuition behind using an interface in Java

Assume you are the head baker of a reputed baking chain, and you want to give instructions to the other bakers under you on the steps they need to follow to bake a cake. You leave them a checklist of things to be done to bake a cake. This is essentially an interface- a checklist! It is a set of methods that you want a class to implement in order to accomplish a certain task.

Polymorphism in JAVA is an essential feature that must be known by the coding students. Read it now through the article.

interface BiscuitBakingService{

 public void mixIngredients();

 public void bakeBiscuit();

 public void frostBiscuit();

}

Example:- biscuit baking service example in java interface

Now, each baker under the head baker may have his/her own way to carry out each of the different tasks, depending on whether they are baking a Cream biscuit or a Truffle biscuit. So, they can implement these methods in their own ways.

Here is another example to understand where interfaces are essential –

Assume you are building out a version of the Angry Birds game. Angry Birds is a fun game where the birds can be put on a slingshot, to protect their eggs from certain pigs. Your task: you have a few different kinds of birds, and you need to make them fly.

Where are java interfaces essential?

  • We could implement it in the following way- using a Bird class as a parent class, and extending specific bird classes from the parent Bird class-

Example-

class Bird{
 //some properties of a bird
 String colour;
 String size;
 public void fly()
 {
   System.out.println("I can fly!");
 }
}
class Bluebird extends Bird
{
public void fly()
 {
 System.out.println("I can fly very far and high!");
 }
}
class Canary extends Bird{
public void fly()
 {
    System.out.println("I can't fly all that high..");
 }
}

This seems alright so far, but suppose now you decide you want to make a space-themed version of Angry Birds, where you introduce a rocket, and you want to make the rocket fly. Oops! The rocket is not a bird, so you cannot extend the Bird class from the Rocket class. And this is where Interfaces come in. With an interface, you can abstract out the fly method to a new class-like object(the interface), and make all your relevant classes implement this interface.

Every Java class is an example of encapsulation because we write everything within the class only that binds variables and methods together and hides their complexity from other classes. Another example of encapsulation is a capsule. Basically, a capsule encapsulates several combinations of medicine. Read more about it in the article by Eduriefy.

interface Flyable{
 public void fly();
}
class Canary extends Bird implements Flyable{
public void fly()
 {
    System.out.println("I can't fly all that high..");
 }
}
class Rocket implements Flyable{
 public void fly()
 {
   System.out.println("I am zooming out into space!");
 }
}

This way, you can abstract out the flying property of an object from its definition by using an Interface. I hope you are now beginning to see the utility of interfaces.

Significant Java interface points

  • One of the fundamental ideas of Java programming, interfaces are heavily utilized in Java design patterns.
  • An interface gives guidelines for what and how a class should perform. In Java, an interface essentially consists of a collection of methods that a class may or may not use.
  • It is also capable of carrying out a task. Interfaces do not have bodies in their methods.
  • Classes implement these abstract methods before using them.
  • In Java, we primarily employ interfaces as a technique to achieve abstraction and multiple inheritances.
  • Other classes must adhere to a set of specifications provided by an interface.
  • A Java program can implement several Java interfaces.
  • A Java class can implement numerous Java interfaces. An interface’s methods are all implicitly public and abstract. Since these methods are abstract, just their method signatures are present.
  • The IS-A relationship of inheritance between two classes is also represented via a Java interface.
  • Multiple interfaces may be inherited by or extended by an interface.
  • In our class, we can implement multiple interfaces.
  • Since Java 8, static and default methods are permitted in interfaces.
  • Since Java 9, private methods may also be included in an interface. The details about this have been discussed in the coding courses. 

Algorithms in JAVA Interface

Problem:- 

interface triangle{

 void getArea(int length, int breadth);

}

// implement the triangle interface

class Rectangle implements Polygon {

  // implementation of the abstract method

  public void getArea(int length, int breadth) {

    System. out.println(“The area of the rectangle is ” + (length * breadth));

  }

}

class Main {

  public static void main(String[] args) {

    Rectangle r1 = new Rectangle();

    r1.getArea(7, 4);

  }

}

Solution:- 

The area of the rectangle is 28.

Java’s interface and class differences

  • An interface object cannot be instantiated or created, in contrast to a class.
  • An interface’s methods should all be marked as abstract.
  • A class can have constructors but an interface cannot.
  • Instance fields are incompatible with interfaces. Only fields that are both static and final can be found in it.
  • An interface is implemented by a class; it cannot be expanded or inherited by a class.
  • A class or another interface cannot implement an interface.

What a Java Interface Should Have

The following characteristics of an interface include

  • Implicitly, an interface is abstract. The keyword abstract is not required when declaring an interface.
  • We don’t need to use the abstract keyword when declaring methods inside an interface because every method of an interface is implicitly abstract.
  • An interface’s methods are all implicitly public.
  • An interface’s variables are all public, static, and final. In other words, instance variables cannot be declared in interfaces; only constants may.

Benefits of a Java Interface

  • To achieve data abstraction, user interfaces.
  • They are also used to provide Java’s multiple inheritance feature.
  • They are also used by us to achieve lax coupling.

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Opportunities in JAVA and Salary

Once you acquaint yourself with the knowledge of JAVA and other coding courses online you can get many opportunities in big companies. Some of them are as follows:-

  • JAVA Stack Developer- 20k to 25k per month.
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Frequently Asked Questions (FAQs)

Question:- WHAT IS an interface in Java give example?

Answer:- An interface is a fully abstract class. It includes a group of abstract methods (methods without a body). We use the interface keyword to create an interface in Java. For example, interface Language { public void getType(); public void getVersion().

Question:- What are Java interface types?

Answer:-Interfaces in Java. Singleton Class in Java. LinkedList in Java. Convert a String to Character Array in Java.

Question:- What is the purpose of interfaces in Java?

Answer:- An interface in Java is a specification of method prototypes. Whenever you need to guide the programmer or make a contract specifying how the methods and fields of a type should be you can define an interface.

Question:- What is the difference between class and interface?

Answer:- A class describes the attributes and behaviors of an object. An interface contains behaviors that a class implements. A class may contain abstract methods and concrete methods. An interface contains only abstract methods.

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