[Mini tutorial] Comparing enums (the right way)

[Botre]

An enum type member is implicitly static and final, it will always reference the same object.

 

I never ever want to see enum comparison with the equals method again. Use "==".

 

Let's create a simple Animal enum:

enum Animal {

DOG, CAT, MOUSE;

}

And a Cage class:

class Cage {

private final Animal animal;

public Cage(final Animal animal) {
this.animal = animal;
}

public final Animal getAnimal() {
return animal;
}

}

The following will thrown a null pointer exception:

Since the first cage's animal is null, calling the equals() method on it will throw an exception!

new Cage(null).getAnimal().equals(new Cage(Animal.DOG).getAnimal()); 

The following will return false:

The first cage's animal is still null, however "==" is not a class method but an operator that allows null on both sides.

You are not calling a method on null, therefore no exception will be thrown

new Cage(null).getAnimal() == new Cage(Animal.DOG).getAnimal();

The following will return true: 

new Cage(Animal.DOG).getAnimal().equals(new Cage(Animal.DOG).getAnimal());

The following will also return true:

An enum type member is implicitly static and final, it will always reference the same object.

You can safely use the "==" operator! AND ALWAYS SHOULD

new Cage(Animal.DOG).getAnimal() == new Cage(Animal.DOG).getAnimal();

Edited August 12, 2016 by Botre

[liverare]

Your justification is convincing, but I'm not comfortable running comparisons against non-primitive/non-wrapped-primitive-object types. Maybe I'll break the habit.

Edited September 10, 2016 by liverare

[Sysm]

Y yu no scriptor? 

[Transporter]

Wise words from lord Botre.