Should toString() ever return null? [duplicate]

Question

Should the method toString() in java ever return null if no conversion could be done or should it return an empty string in that case instead?

Answer 1

null is not String so it is not allowed to return here. Check Java Docs:

Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

it should return a meaningful string representation of the object. I wrote an example of how to use it and why it is useful:

public class Car {
    private String make;
    private int year;
    public Car(String make, int year) {
        this.make = make;
        this.year = year;
    }    

    @Overrride
    public String toString() {
        return "Car Make:" + make + "; Built Year: " + year;
    }
}

Example:

Car myCar = new Car("Nissan", 1999);
Car yourCar = new Car("BMW", 2018);
System.out.println(myCar);  // call toString() implicitly
System.out.println(yourCar);

It will print 2 lines and you can easily read the text and know which is your car!

Car Make:Nissan; Built Year: 1999
Car Make:BMW; Built Year: 2018