Question

What is difference between abstract class and interface?

Answer 1

An interface is an empty shell, there are only the signatures (name / params / return type) of the methods. The methods do not contain anything. The interface can't do anything. It's just a pattern.

Answer 2

Abstract classes, unlike interfaces, are classes. There are more expensive to use because there is a lookup to do when you inherit from them.

Abstract classes look a lot like interfaces, but they have something more : you can define a behavior for them. It's more about a guy saying "these classes should look like that, and they got that in common, so fill in the blanks!".

Answer 3

interface example:

Answer 4

// I say all motor vehicles should look like that :
interface MotorVehicle
{
void run();

int getFuel();
}

// my team mate complies and write vehicle looking that way
class Car implements MotorVehicle
{

int fuel;

void run()
{
print("Wrroooooooom");
}


int getFuel()
{
return this.fuel;
}
}

Answer 5

abstract example:

Answer 6

// I say all motor vehicles should look like that :
abstract class MotorVehicle
{

int fuel;

// they ALL have fuel, so why let others implement that ?
// let's make it for everybody
int getFuel()
{
return this.fuel;
}

// that can be very different, force them to provide their
// implementation
abstract void run();


}

// my team mate complies and write vehicle looking that way
class Car extends MotorVehicle
{
void run()
{
print("Wrroooooooom");
}
}