Show me the pain!

... or "what does this look like in practice?"

Consider this snippet of code:

...
if (car.getDrivetrain().getEngine().getGasType() == GasType.DIESEL) {
   // TODO: do some cool stuff...
}
...

What stands out?

Consider this snippet of code:

...
if (car != null 
       && car.getDrivetrain() != null 
       && car.getDrivetrain().getEngine() != null 
       && car.getDrivetrain().getEngine().getGasType() == DIESEL) {
   // TODO: do some cool stuff...
}
...

Now what do you see?

Rating: LESS BAD

Consider this snippet of code:

...
if (car.getTypeOfGasUsed() == GasType.DIESEL) {
   // TODO: do some cool stuff...
}
...

That's a lot nicer!

Rating: GOOD

Look at this:

...
if (car.usesGasType(GasType.DIESEL)) {
   // TODO: do some cool stuff...
}
...

Do you see the difference?

Rating: BEST

Sounds Great

How do I get started?

Don't do this...

class Car {
   ...
   boolean willRunOn(GasType gasType) {
      return drivetrain != null 
                && drivetrain.getEngine() != null 
                && drivetrain.getEngine().getGasType() == gasType;
   }
   ...
}

Why not?

Do this...

class Car {
   ...
   boolean willRunOn(GasType gasType) {
      return drivetrain != null && drivetrain.willRunOn(gasType);
   }
   ...
}

class Drivetrain {
   ...
   boolean willRunOn(GasType gasType) {
      return engine != null && engine.willRunOn(gasType); 
   }
   ...
}

class Engine {
   ...
   boolean willRunOn(GasType gasType) {
      return correctGasType == gasType;
   }
   ...
}

same name: coincidence, NOT an interface

Downsides?

• Can have overly specific methods
• Lots of code up front to save pain on changes in the future

Do This

Not This

boolean willRunOn(GasType gasType);

boolean willRunOnDiesel();
boolean willRunOnPetrol();
boolean willRunOnJetFuel();
boolean willRunOnRedBull();
boolean willRunOnPropane();
...