인터페이스는 인터페이스 그 이상입니다. 행동입니다.

interface Moveable
{
void move(String newAddress);
}

interface Driveable
{
void drive(Driver driver);
}

interface Transport
{
void addStuff(Object stuff);
Object removeStuff();
}

class Wheel implements Moveable
{
...
}

class Car implements Moveable, Drivable, Transport
{
...
}

class Skateboard implements Moveable, Driveable
{
...
}

static interface WallBuilder
{
void buildWall();
}

static class WorkerRobot implements WallBuilder
{
void buildWall()
 {
…
 }
}
static class GuardRobot implements WallBuilder
{
void buildWall()
 {
…
 }
}
static class WateringCan
{
…
}

물 뿌리개는 벽을 만들 수 없습니다(WallBuilder 인터페이스를 구현하지 않음).

public static void main(String[] args)
{
 //add all robots to a list
 ArrayList robots = new ArrayList();
 robots.add(new WorkerRobot());
 robots.add(new GuardRobot());
 robots.add(new WateringCan());

 //build a wall if you can
 for (Object robot: robots)
 {
  if (robot instanceof WallBuilder)
  {
   WallBuilder builder = (WallBuilder) robot;
   builder.buildWall();
   }
  }
 }
}