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| layout | pattern | |||
|---|---|---|---|---|
| title | Facade | |||
| folder | facade | |||
| permalink | /patterns/facade/ | |||
| pumlid | BSP15eCm20N0gxG7CEoz3ILKqvTW7dpq-hhehERTJ7fMJU-l7PYn4ZbVPMlOyvEXBeT13KMEGQtdnM2d7v-yL8sssJ8PKBUWmV64lYnSbHJoRqaVPUReDm00 | |||
| categories | Structural | |||
| tags |
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Provide a unified interface to a set of interfaces in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use.
Real world example
How does a goldmine work? "Well, the miners go down there and dig gold!" you say. That is what you believe because you are using a simple interface that goldmine provides on the outside, internally it has to do a lot of stuff to make it happen. This simple interface to the complex subsystem is a facade.
In plain words
Facade pattern provides a simplified interface to a complex subsystem.
Wikipedia says
A facade is an object that provides a simplified interface to a larger body of code, such as a class library.
Programmatic Example
Taking our goldmine example from above. Here we have the dwarven mine worker hierarchy
public abstract class DwarvenMineWorker {
private static final Logger LOGGER = LoggerFactory.getLogger(DwarvenMineWorker.class);
public void goToSleep() {
LOGGER.info("{} goes to sleep.", name());
}
public void wakeUp() {
LOGGER.info("{} wakes up.", name());
}
public void goHome() {
LOGGER.info("{} goes home.", name());
}
public void goToMine() {
LOGGER.info("{} goes to the mine.", name());
}
private void action(Action action) {
switch (action) {
case GO_TO_SLEEP:
goToSleep();
break;
case WAKE_UP:
wakeUp();
break;
case GO_HOME:
goHome();
break;
case GO_TO_MINE:
goToMine();
break;
case WORK:
work();
break;
default:
LOGGER.info("Undefined action");
break;
}
}
public void action(Action... actions) {
for (Action action : actions) {
action(action);
}
}
public abstract void work();
public abstract String name();
static enum Action {
GO_TO_SLEEP, WAKE_UP, GO_HOME, GO_TO_MINE, WORK
}
}
public class DwarvenTunnelDigger extends DwarvenMineWorker {
private static final Logger LOGGER = LoggerFactory.getLogger(DwarvenTunnelDigger.class);
@Override
public void work() {
LOGGER.info("{} creates another promising tunnel.", name());
}
@Override
public String name() {
return "Dwarven tunnel digger";
}
}
public class DwarvenGoldDigger extends DwarvenMineWorker {
private static final Logger LOGGER = LoggerFactory.getLogger(DwarvenGoldDigger.class);
@Override
public void work() {
LOGGER.info("{} digs for gold.", name());
}
@Override
public String name() {
return "Dwarf gold digger";
}
}
public class DwarvenCartOperator extends DwarvenMineWorker {
private static final Logger LOGGER = LoggerFactory.getLogger(DwarvenCartOperator.class);
@Override
public void work() {
LOGGER.info("{} moves gold chunks out of the mine.", name());
}
@Override
public String name() {
return "Dwarf cart operator";
}
}
To operate all these goldmine workers we have the facade
public class DwarvenGoldmineFacade {
private final List<DwarvenMineWorker> workers;
public DwarvenGoldmineFacade() {
workers = new ArrayList<>();
workers.add(new DwarvenGoldDigger());
workers.add(new DwarvenCartOperator());
workers.add(new DwarvenTunnelDigger());
}
public void startNewDay() {
makeActions(workers, DwarvenMineWorker.Action.WAKE_UP, DwarvenMineWorker.Action.GO_TO_MINE);
}
public void digOutGold() {
makeActions(workers, DwarvenMineWorker.Action.WORK);
}
public void endDay() {
makeActions(workers, DwarvenMineWorker.Action.GO_HOME, DwarvenMineWorker.Action.GO_TO_SLEEP);
}
private static void makeActions(Collection<DwarvenMineWorker> workers,
DwarvenMineWorker.Action... actions) {
for (DwarvenMineWorker worker : workers) {
worker.action(actions);
}
}
}
Now to use the facade
DwarvenGoldmineFacade facade = new DwarvenGoldmineFacade(); facade.startNewDay(); // Dwarf gold digger wakes up. // Dwarf gold digger goes to the mine. // Dwarf cart operator wakes up. // Dwarf cart operator goes to the mine. // Dwarven tunnel digger wakes up. // Dwarven tunnel digger goes to the mine. facade.digOutGold(); // Dwarf gold digger digs for gold. // Dwarf cart operator moves gold chunks out of the mine. // Dwarven tunnel digger creates another promising tunnel. facade.endDay(); // Dwarf gold digger goes home. // Dwarf gold digger goes to sleep. // Dwarf cart operator goes home. // Dwarf cart operator goes to sleep. // Dwarven tunnel digger goes home. // Dwarven tunnel digger goes to sleep.
Use the Facade pattern when
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