6.14. Constructors With Parameters¶

Take a look at this simple Celebrity class:

class Celebrity{
  String name;

  public Celebrity(){
    System.out.println("A new celebrity has been created!");
  }

  public void setName(String n){
    name = n;
  }
}

I bet you noticed that there are a lot of similarities between the structure of the constructor and our method setName. For example, I notice that both of them start with the modifier public. I also notice that both of them have a name, followed by a set of parentheses. Does that mean it’s possible to include parameters in our constructors too?

You betcha! In fact, in many cases you will want to include parameters in your constructor because it makes instantiating an object with a specific state a lot easier. For example, I could assign our name instance variable to a value of my choosing if I write my constructor like this:

class Celebrity{
  String name;

  public Celebrity(String n){
    name = n;
    System.out.println("A new celebrity has been created!");
  }

  public void setName(String n){
    name = n;
  }
}

Think of what this allows me to do. I can now make as many Celebrity objects as I would like, all with different states! Don’t believe me? Take a look at this main method where I instantiate three very different Celebrity objects using the Celebrity class defined above:

class Main{
  public static void main(String[] args){
    Celebrity bey = new Celebrity("Beyonce");
    Celebrity rihrih = new Celebrity("Rihanna");
    Celebrity juice = new Celebrity("Juice WRLD");
  }
}

If we didn’t include parameters within our constructor, we would have to write a lot more code. Remember our dot operator?

class Main{
  public static void main(String[] args){
    Celebrity bey = new Celebrity();
    bey.name = "Beyonce";
    Celebrity rihrih = new Celebrity("Rihanna");
    rihrih.setName("Rihanna");
    Celebrity juice = new Celebrity("Juice WRLD");
    juice.setName = "Juice WRLD";
  }
}

You can add as many parameters to your constructors as you would like! Here is an example of a Celebrity constructor that contains all the parameters:

class Celebrity{
  String name;
  int age;
  String type;
  boolean isAlive;

  public Celebrity(String n, int a, String t, boolean d){
    name = n;
    age = a;
    type = t;
    isAlive = d;
    System.out.println("A new celebrity has been created!");
  }
}

class Main{
  public static void main(String[] args){
    Celebrity bey = new Celebrity("Beyonce", 39, "Singer", true);
    Celebrity rihrih = new Celebrity("Rihanna", 32, "Singer", true);
    Celebrity juice = new Celebrity("Juice WRLD", 21, "Rapper", false);
  }
}

Once thing is bothering me about my constructor’s parameters though; their names suck! If I look at this code 5 years from now, I’m probably not going to remember what I was thinking when I wrote “n”, “a”, “t”, and “d”. I know that I can name parameters whatever I would like but I gotta think about what makes my program easier to read, both for me and other programmers reviewing my code.

But honestly, it feels like I already chose the best names when I declared the instance variables of this class. Is there a way that I can name my parameters the same thing and not confuse my computer?

AP CSA

6.14. Constructors With Parameters¶