Interfaces

Pure abstraction with interface keyword

Interview Relevant: Interface vs Abstract class
6 min read

Interfaces

Interfaces define contracts. Classes can implement multiple interfaces.

Code Examples

Multiple inheritance via interfaces

java
1
2interface Flyable {
3    void fly();
4}
5
6interface Swimmable {
7    void swim();
8}
9
10class Duck implements Flyable, Swimmable {
11    public void fly() {}
12    public void swim() {}
13}
14

Use Cases

  • Multiple inheritance
  • Strategy pattern
  • Dependency injection

Common Mistakes to Avoid

  • Using interfaces for state
  • Forgetting methods are public by default