Java Interfaces– Complete Guide

1. What is an Interface in Java?

An interface in Java is a blueprint of a class that only contains method signatures (no implementation). It is used to achieve abstraction and multiple inheritance in Java.

💡 Key Points:

• No method implementation – Only method declarations.
• Implemented by classes – Classes provide the actual implementation of the methods.
• Supports multiple inheritance – A class can implement multiple interfaces.

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2. Creating a Java Interface

Step 1: Define an Interface

interface WordPress {
    void publishPost(String title, String content);  // Abstract method
}

🔹 Explanation:

• This interface defines the publishPost() method.
• Any class that implements this interface must provide an implementation.

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Step 2: Implement the Interface

WordPressAPI implements WordPress {
    private String apiUrl;
    private String username;
    private String password;

    public WordPressAPI(String apiUrl, String username, String password) {
        this.apiUrl = apiUrl;
        this.username = username;
        this.password = password;
    }

    @Override
    public void publishPost(String title, String content) {
        // Simulating an API request (Replace this with real API call)
        System.out.println("Connecting to WordPress API at: " + apiUrl);
        System.out.println("Authenticating as: " + username);
        System.out.println("Publishing Post:");
        System.out.println("Title: " + title);
        System.out.println("Content: " + content);
        System.out.println("Post published successfully!");
    }
}

🔹 Explanation:

• WordPressAPI implements the WordPress interface.
• It provides the actual implementation of publishPost().

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Step 3: Using the Interface

class Main {
    public static void main(String[] args) {
        // WordPress API credentials (Replace with real values)
        String apiUrl = "https://example.com/wp-json/wp/v2/posts";
        String username = "admin";
        String password = "password";

        // Creating an instance of WordPressAPI
        WordPress myBlog = new WordPressAPI(apiUrl, username, password);

        // Publishing a blog post
        myBlog.publishPost("My First Post", "This is the content of my blog post.");
    }
}

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3. How It Works

✅ Step 1: The WordPress interface defines the method but does not implement it.
✅ Step 2: The WordPressAPI class implements the interface and provides the real functionality.
✅ Step 3: The Main class uses the WordPressAPI class via the WordPress interface.

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4. Benefits of Using Interfaces

✅ Loose Coupling

• The Main class does not depend on the actual implementation (WordPressAPI).
• If we need a different WordPress API implementation, we can easily replace it.

✅ Multiple Implementations

• We can create another class (WordPressMockAPI) to simulate API responses for testing.

✅ Flexibility & Scalability

• New API implementations can be added without modifying existing code.