Try It Yourself - SyntaxStudy Editor

HTML / CSS / JS

import java.util.List;

// Interface defining a contract
interface Printable {
    void print();                            // implicitly public abstract
}

interface Saveable {
    boolean save(String destination);
}

// Interface extending multiple interfaces
interface Document extends Printable, Saveable {
    String getTitle();
    int    getPageCount();
}

// Concrete implementation
class PdfDocument implements Document {
    private final String title;
    private final List<String> pages;

PdfDocument(String title, List<String> pages) {
        this.title = title;
        this.pages = pages;
    }

@Override public String getTitle()     { return title; }
    @Override public int    getPageCount() { return pages.size(); }

@Override public void print() {
        System.out.println("=== PDF: " + title + " ===");
        for (int i = 0; i < pages.size(); i++) {
            System.out.printf("Page %d: %s%n", i + 1, pages.get(i));
        }
    }

@Override public boolean save(String destination) {
        System.out.printf("Saving '%s' to %s%n", title, destination);
        return true;  // success
    }
}

public class InterfaceDemo {

// Programming to the interface — works for any Document implementation
    static void processDocument(Document doc) {
        System.out.println("Processing: " + doc.getTitle()
            + " (" + doc.getPageCount() + " pages)");
        doc.print();
        doc.save("/tmp/" + doc.getTitle().replaceAll("\\s+", "_") + ".pdf");
    }

public static void main(String[] args) {
        PdfDocument doc = new PdfDocument(
            "Java Guide",
            List.of("Introduction to Java", "Data Types", "Control Flow")
        );
        processDocument(doc);
    }
}