What is the difference between an abstract class and an interface?

An abstract class allows its subclasses to override the methods defined in it. It is never instantiated and a class can inherit from a single class, as Java doesn't support for Multiple Inheritance. It may contain both abstract and non-abstract methods.

An interface has public, abstract methods and may have public, static and final variables (read only). It introduces multiple inheritance by a class implementing several interfaces.

An example:

interface Movable
{
abstract move ();
}
abstract class Mammal
{
void getHeight(float height)
{ ... }
abstract eat();
}
abstract class Vehicle
{
void getSizeofSeat(float seatSize)
{ ... }
abstract engineType();
}
class Student extends Mammal implements Move
{
......
getheight(height);
void eat()
{.......}
void move();
}
class Car extends Vehicle implements Move
{
......
getSizeofSeat(float seatSize
void engineTypr()
{.......}
void move();
}

Hence Student and Car is not related but they can still implement the Move interface.

Moreover,an abstract class can have concrete methods while an interface cannot.