Static Factory Method is creating a new object everytime its invoked

Question

In Effective Java its mentioned that "Unlike constructors static factory methods are not required to create a new object each time they're invoked".

class Car{
     String color;
     Boolean spoiler;

     public Car(String s){
        color=s;
        spoiler = false;
     }

     public static Car redCar(){
        return new Car("red");
    }
  }

In Main Class:

    Car c2 = Car.redCar();
    Car c3 = Car.redCar();        

c2 and c3 are different objects. I did not get the context of "not required to create a new object each time invoked".

Answer 1

Because that's what you do:

public static Car redCar(){
    return new Car("red");
}
        //  ^ here

If you want to return the same value you can do something like:

private static final Car RED_CAR = new Car("red");

public static Car redCar(){
    return RED_CAR;
}

The point is that calling new Car() will always return a new instance. Calling Car.newInstance() means that the Car class can decide what to do.

For example:

private static final Map<String, Car> CARS = new HashMap<>();

public static Car newInstance(final String colour){
    return CARS.computeIfAbsent(colour, Car::new);
}

This uses the Car constructor as a method reference to the new Map.computeIfAbsent method, which calls it if a Car of that colour is not already present in the Map. This is a naive (not threadsafe) cache implementation.

So:

final Car one = Car.newInstance("red");
final Car two = Car.newInstance("red");
System.out.println(one == two) // true