Question

Name the different types of constructors that a designer can provide in a class. Provide an example with a class showing many constructors.

Answer 1

By default, if you do not implement a constructor, the compiler will use an empty constructor (no parameters and no code). The following code will create an instance of the MyObject class using the default constructor. The object will have the default vauesfor all the attributes since no parameters were given.

MyObject obj = new MyObject();

Another type of constructor is one with no parameters (no-arg constructor). It is similar to the default, except you actually create this constructor. The contents of the the constructor may include anything. To call a no-arg constructor, use the same line of code as above. The constructor can look like the one below:

public MyObject() {
System.out.println("This is a no-arg constructor");
}

Lastly there is the parameterized constructor. This type of constructor takes in parameters as inputs to assign to values in the newly created object. You call a parameterized constructor as follows:

MyObject obj = new MyObject("Bob", 20);

The constructor will look like this:

public MyObject(String name, int age) {
this.name = name;
this.age = age;
}

In the constructor, the keyword "this" refers to the object, so this.name is a private global variable that is being set equal to the inputted value for name, in this case "Bob".

Hope this helps!