Reduce complexity of an if statement containing lots of if statements

Question

I have a method for which I need to reduce the cyclomatic complexity. But am unsure how to go about it.

public boolean isEqual(Car car) { if (this.id != car.id) return false; if (this.reg != car.reg) return false; if (this.vin != car.vin) return false; if (this.make != car.make) return false; if (this.model != car.model) return false; return true; }

There are more if statements like that in the method but I have only included a few. How can I reduce the complexity? Sorry if not correctly formatted as I have written this on my mobile.

Complexity in what sense?

Maroun
– Maroun

2015-02-25 19:09:51 +00:00
Commented Feb 25, 2015 at 19:09 — Maroun
– Maroun, Commented Feb 25, 2015 at 19:09
@maroun maroun. In terms of the different paths it can take

Waz
– Waz

2015-02-25 19:31:16 +00:00
Commented Feb 25, 2015 at 19:31 — Waz
– Waz, Commented Feb 25, 2015 at 19:31
Are you using Java 8?

Maroun
– Maroun

2015-02-26 07:57:31 +00:00
Commented Feb 26, 2015 at 7:57 — Maroun
– Maroun, Commented Feb 26, 2015 at 7:57

krillgar · Accepted Answer · 2015-02-25 19:14:16Z

There really is no way to make it that much cleaner. As Maroun questioned in the comments, there isn't really that much complexity. However, you can get rid of the "if" statements, and it would be a little easier to read this way:

public boolean isEqual(Car car) { return this.Id == car.id && this.reg == car.reg && this.vin == car.vin && this.make == car.make && this.model == car.model; }

You can continue to add as many as you need there. This will act somewhat like your "if" statements, as the second it finds a "false" result, it will stop checking any others, and just return the false result.

Alan Hay · Accepted Answer · 2015-02-25 21:08:56Z

You could use a 3rd party library such as Apache Commons lang which has utility methods like:

public boolean isEqual(Car car) { return new EqualsBuilder().reflectionEquals(this, car); }

http://commons.apache.org/proper/commons-lang/apidocs/org/apache/commons/lang3/builder/EqualsBuilder.html

However ask if you really need to compare all fields: CarA and CarB can surely only be equal if they have the same id (or vin or registration).

public boolean isEqual(Car car) { //return this.reg= other.reg;? //return this.vin= other.vin;? return this.id = other.id; }

reflectionEquals is somewhat slower than doing .append(lhs, rhs) with each of the fields on which equality is measured though

Ricardo Silva · Accepted Answer · 2015-02-25 19:13:16Z

you can do:

 public boolean isEqual(Car car) { return !(this.id != car.id || this.reg != car.reg || this.vin != car.vin || this.make != car.make || this.model != car.model); }

user949300 · Accepted Answer · 2015-02-25 19:18:16Z

Some would write it this way, a bit clearer (@krillgar suggested this too)

public boolean isEqual(Car car) { return (this.id == car.id) && (this.reg == car.reg) && ... }

However, if even this seems too long, you should split it up into smaller tests for "sameness".

public boolean isEqual(Car car) { return this.sameMakeAndModel(car) && this.sameRegistrationInfo(car) && ... } boolean sameMakeAndModel(Car car) { return (this.make == car.make) && (this.model == car.model) && ... check engine size, colors? } boolean sameRegistrationInfo(Car car) { return (this.vin == car.vin) && (this.reg == car.reg) && ... }

Whether these sub-tests should be public, protected or private is TBD.

p.s. Out of paranoia, add a test that the car argument is non-null!

The "danger" of this approach is repetition of checking properties throughout the different methods. Granted, in this scenario, an extra boolean compare isn't that big of a deal, but if the OP continues this pattern in more complex scenarios, it could result in a lot of overhead.

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