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Java OOP
course content

Course Content

Java OOP

Java OOP

1. How to Work With IDE?
Installing JavaInstalling IntelliJ IDEA (MacOS)Installing IntelliJ IDEA (Windows)Code Editor Main FeaturesDebuggerPackagesHow to do Tasks?
2. OOP
What is OOP? OOP Principles: Inheritance Challenge: InheritanceOOP Principles: PolymorphismChallenge: PolymorphismOOP Principles: EncapsulationOOP Principles: Abstraction Challenge: Abstraction
3. Interface
What is Interface?Challenge: InterfaceAbstract Class vs InterfaceDefault MethodsStatic MethodsSummary

book
Default Methods

Abstract class vs Interface: The Interface Strikes Back!

Previously, methods with implementations could only exist in abstract classes, but starting from Java 8, they also appeared in interfaces.

Let's take a look at the syntax for declaring a default method:

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We need default methods for the same purposes as regular methods in Java. We use them when we need an implementation in the method and when we want to implement only the interface without additional classes. Let's consider a small example using default methods:

java

Main

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package com.example;

public class Main {
    public interface Greeting {
        default void sayHello() {
            System.out.println("Hello from the interface!");
        }

        void greet(String name);
    }

    public static class GreetingImpl implements Greeting {
        @Override
        public void greet(String name) {
            System.out.println("Hello, " + name + "!");
        }
    }

    public static void main(String[] args) {
        GreetingImpl greetingImpl = new GreetingImpl();
        greetingImpl.sayHello(); // Output: Hello from the interface!
        greetingImpl.greet("Alice"); // Output: Hello, Alice!
    }
}

In this example, the interface Greeting contains a default method sayHello() with a default implementation. The class GreetingImpl implements this interface and overrides the greet() method. In the main method, an instance of GreetingImpl is created and both methods are called.

question mark

What is the purpose of a default method in a Java interface?

Select the correct answer

Everything was clear?

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Thanks for your feedback!

SectionΒ 3. ChapterΒ 4
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