Java Programming · Module 7 of 10

Interfaces and abstract classes

Define contracts with interfaces and partial blueprints with abstract classes.

📖 Key ideas

An interface lists methods a class promises to implement.
class Car implements Vehicle, Serializable: a class can implement many interfaces.
An abstract class cannot be instantiated and can mix implemented and abstract methods.
Interfaces can have default methods with a body (Java 8+).
Program to interfaces: List<String> list = new ArrayList<>();

💡 Real-life example: An interface is a job description; any person (class) who meets it can take the job.

interfaceContract of methods

implementsFulfils an interface

abstract classClass that cannot be instantiated

default methodInterface method with a body