Interface vs Abstract Class

When to use which

Interview Relevant: Very common interview question
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Interface vs Abstract Class

Choosing between interface and abstract class depends on design needs.

  • Interface ā†’ multiple inheritance
  • Abstract class ā†’ shared state + behavior
  • Interface ā†’ contract
  • Abstract ā†’ partial implementation

Code Examples

Interface vs abstract class usage

java
1
2interface Flyable {
3    void fly();
4}
5
6abstract class Bird {
7    abstract void sound();
8    void eat() {}
9}
10

Use Cases

  • Design decisions
  • Framework APIs

Common Mistakes to Avoid

  • Using abstract class when interface fits
  • Ignoring multiple inheritance limitation