Predicates vs if statements

Question

I have seen in some projects that people use Predicates instead of pure if statements, as illustrated with a simple example below:

    int i = 5;     // Option 1     if (i == 5) {         // Do something         System.out.println("if statement");     }      // Option 2     Predicate<Integer> predicate = integer -> integer == 5;     if (predicate.test(i)) {         // Do something         System.out.println("predicate");     } 

What's the point of preferring Predicates over if statements?

Answer 1

Using a predicate makes your code more flexible.

Instead of writing a condition that always checks if i == 5, you can write a condition that evaluates a Predicate, which allows you to pass different Predicates implementing different conditions.

For example, the Predicate can be passed as an argument to a method :

public void someMethod (Predicate<Integer> predicate) {     if(predicate.test(i)) {         // do something         System.out.println("predicate");     }     ... } 

This is how the filter method of Stream works.

Answer 2

For the exact example that you provided, using a Predicate is a big over-kill. The compiler and then the runtime will create:

1. a method (de-sugared predicate)
2. a .class that will implement java.util.Predicate
3. an instance of the class created at 2

all this versus a simple if statement.

And all this for a stateless Predicate. If your predicate is statefull, like:

 Predicate<Integer> p = (Integer j) -> this.isJGood(j); // you are capturing "this" 

then every time you will use this Predicate, a new instance will be created (at least under the current JVM).

The only viable option IMO to create such a Predicate is, of course, to re-use it in multiple places (like passing as arguments to methods).