So, the class is being fully constructed in multiple lines of code. What I mean by that is, that, first of all, I will create an empty object, then I will call setter to set one parameter, then another setter to set another parameter, and so on.
Another drawback is that the class object now will be fully constructed in multiple lines. But it has some serious drawbacks of its own.įirst of all, since we are setting values in the setter methods, we are basically allowing the user to mutate the class variables. It does not have any limitations of the telescoping constructor pattern. This seems pretty clean, easy and very readable as well. Then, after we have created an object, we can call the appropriate setter methods to assign values to the class variables. Using this approach, we can create an object of the Person class without passing any values, as it has a no-arg default constructor. Let’s look at an example of this approach. The JavaBeans approach dictates that the class should have a public no-arg constructor and public setter and getter methods. To overcome these limitations, came another approach, known as the JavaBeans pattern. So, this approach had a lot of limitations. The compiler won’t complain, but the program will misbehave at runtime. Plus, with identical types of parameters (as in this example), the user might mistakenly reverse the order of two parameter values while passing them in the constructor.
JAVA CONSTRUCTOR OPTIONAL PARAMETERS CODE
Just imagine the code base of a class with 20 parameters with this approach. So, that is one disadvantage of this pattern.įurthermore, this was a small example so that you can grasp the concept easily, and so it only had 5 arguments. So, the user will have to call the constructor at line 18 and will have to pass middleName‘s default value as well, although he doesn’t need to set it. For this purpose, we will not be able to create a new constructor, as there is already one constructor with three String parameters. But, what if I want to set facebookId but not middleName. For example, if the user wants to set firstName, lastName and middleName, then he can call the constructor at line 22 and other parameters will be set to default values. Now, the user just needs to find a suitable constructor according to his use case, and use it. Eventually, the calls end up with the constructor which has all the parameters and in that constructor, we set all the values to the passed values. We have multiple constructors calling another constructor while setting one more argument with the default value. What happens here is chaining of constructor calls. We have a constructor with only the required parameters that we can call if we only want to set the required parameters, and the optional parameters will be set with default values. Let’s understand this pattern with an example.Īs you can see above, we have created multiple constructors with a different number of parameters. The first approach that was devised to get around this problem, was the Telescoping Constructor Pattern. So, let’s go ahead and look at the first approach. This will be the problem statement that we will be trying to solve in this blog. Now, our constructor can still work here, but if the user constructing an object of our class only needs to set 2 required arguments and not the 18 optional arguments, then he will have to still pass all the 20 arguments, where, for the ones he doesn’t want to set, he will be passing default values. Now, out of these 20 arguments, only 2 are my required arguments, and 18 are optional, i.e., those are not necessarily required to create the object of the class. I can still create a constructor for this class, but I will have to give 20 parameters to that constructor. Awesome! But, I want to construct an object of a class that has 20 arguments. Pretty simple, right? We can just have a constructor to do that. We want to construct an object of a class. So, let’s discuss the problem statement due to which the Builder Pattern came into existence. But before understanding that, we need to understand why did we come up with the Builder Pattern in the first place. In this blog, we are going to look at what the Builder Pattern is and how does it help us construct objects of classes easily.
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