Difference between class & interface?

Answer 1

An interface is a contract. Any class that implements the interface must implement all the methods defined in the interface or else the contract is broken.

Answer 2

Interfaces are abstract classes basically. Interfaces are classes that only contain abstract methods.

Answer 3

a class is a model for similar objects, an interface is a model for similar behaviours of derived classes

Answer 4

it is also solution for multiple inherit in java