## StarMass

### Instructions

For this last exercise, let's compute the mass of all objects in a galaxy, according their type.

Firstly, let's add a mass property (it will be an integer) to all objects. I let you guess in which class to put it ;)  
You need to add the getter and setter for this property too. You will need to add a mass argument to all the constructors.

In the `Galaxy` class, we will add a new method `computeMassRepartition` which returns a Map. This map will have for key the Strings `Star`, `Planet` or `Other`. The values will be the sum of the mass of the object by their type.

### Usage

Here is a possible ExerciseRunner.java to test your function :

```java
public class ExerciseRunner {

    public static void main(String[] args) {
        Galaxy galaxy = new Galaxy();
        CelestialObject charron = new CelestialObject("Charron", -123.12, 392.238, 32.31, 157);
        CelestialObject lune = new CelestialObject("Lune", 3928.32, 327.239, -12.92, 3987);
        Star betelgeuse = new Star("Betelgeuse", 128.23, -12.82, 32.328, 1289.3, 538595);
        Star altair = new Star("Betelgeuse", 43894.34, -324.43, 9438.23, 123.54, 137273);
        Star bellatrix = new Star("Bellatrix", 584.34, 2103.32, -102.43, 413.2, 5483724);
        Planet naboo = new Planet("Naboo", 17.4389, 8349.1, 8943.92, betelgeuse, 32454);
        Planet tatooine = new Planet("Tatooine", 17.4389, 8349.1, 8943.92, betelgeuse, 2345);
        Planet mercure = new Planet("Mercure", 17.4389, 8349.1, 8943.92, altair, 19438);
        Planet venus = new Planet("Venus", 17.4389, 8349.1, 8943.92, altair, 9283);
        Planet mars = new Planet("Mars", 17.4389, 8349.1, 8943.92, altair, 2183);
        
        galaxy.addCelestialObject(lune);
        galaxy.addCelestialObject(charron);
        galaxy.addCelestialObject(mars);
        galaxy.addCelestialObject(mercure);
        galaxy.addCelestialObject(tatooine);
        galaxy.addCelestialObject(altair);
        galaxy.addCelestialObject(venus);
        galaxy.addCelestialObject(betelgeuse);
        galaxy.addCelestialObject(naboo);
        galaxy.addCelestialObject(bellatrix);
        
        System.out.println(galaxy.computeMassRepartition().toString());
    }
}
```

and its output :

```shell
$ javac *.java -d build
$ java -cp build ExerciseRunner 
{Star=6159592, Planet=65703, Other=4144}
$ 
```

### Notions

[InstanceOf](https://www.baeldung.com/java-instanceof)