Interfaces: Declaration, Multiple Interface Implementation, and default/static Methods0%

Package Architecture, package Declaration, and import Statements

Interfaces: Declaration, Multiple Interface Implementation, and default/static Methods

Intermediate14 min read•Updated: 2026-10-22

🔌 Interfaces: Multiple Implementation & Default Methods

Introduction

An interface is a 100% abstract contract specifying what a class should do, without prescribing how. While Java forbids multiple class inheritance, a class can implement multiple interfaces, achieving complete architectural decoupling.

💻 Multiple Interface Implementation

1interface Printable {
2    void print(); // Public abstract by default
3}
4 
5interface Exportable {
6    void exportToPdf(String filename);
7 
8    // Default method (Java 8+): Provides default implementation without breaking existing classes!
9    default void logExportAudit() {
10        System.out.println("[AUDIT]: Document export event logged.");
11    }
12}
13 
14// Class implementing multiple interfaces:
15public class ReportCard implements Printable, Exportable {
16    private String studentName;
17    private double gpa;
18 
19    public ReportCard(String name, double gpa) {
20        this.studentName = name;
21        this.gpa = gpa;
22    }
23 
24    @Override
25    public void print() {
26        System.out.printf("Report Card: %s | GPA: %.2f%n", studentName, gpa);
27    }
28 
29    @Override
30    public void exportToPdf(String filename) {
31        System.out.println("Exported " + filename + " successfully.");
32        logExportAudit(); // Invokes default method
33    }
34 
35    public static void main(String[] args) {
36        ReportCard rc = new ReportCard("Aarav", 9.5);
37        rc.print();
38        rc.exportToPdf("Aarav_GradeCard.pdf");
39    }
40}

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Package Architecture, package Declaration, and import Statements

Interfaces: Declaration, Multiple Interface Implementation, and default/static Methods

Intermediate14 min read•Updated: 2026-10-22

Study Materials

🔌 Interfaces: Multiple Implementation & Default Methods

Introduction

💻 Multiple Interface Implementation

1interface Printable {
2    void print(); // Public abstract by default
3}
4 
5interface Exportable {
6    void exportToPdf(String filename);
7 
8    // Default method (Java 8+): Provides default implementation without breaking existing classes!
9    default void logExportAudit() {
10        System.out.println("[AUDIT]: Document export event logged.");
11    }
12}
13 
14// Class implementing multiple interfaces:
15public class ReportCard implements Printable, Exportable {
16    private String studentName;
17    private double gpa;
18 
19    public ReportCard(String name, double gpa) {
20        this.studentName = name;
21        this.gpa = gpa;
22    }
23 
24    @Override
25    public void print() {
26        System.out.printf("Report Card: %s | GPA: %.2f%n", studentName, gpa);
27    }
28 
29    @Override
30    public void exportToPdf(String filename) {
31        System.out.println("Exported " + filename + " successfully.");
32        logExportAudit(); // Invokes default method
33    }
34 
35    public static void main(String[] args) {
36        ReportCard rc = new ReportCard("Aarav", 9.5);
37        rc.print();
38        rc.exportToPdf("Aarav_GradeCard.pdf");
39    }
40}

Next Lesson

Package Architecture, package Declaration, and import Statements

Continue learning with hands-on practice, examples, and exercises in the upcoming topic.

Related Lessons

Previous Lesson	Next Lesson
Abstract Classes vs Concrete Classes	Package Architecture, package Declaration, and import Statements

Practice Quiz

Test your understanding of this lesson with 1 questions. Each question has one correct answer.

Previous Next