Inheritence and constructors
- Every class (including abstract classes) must have a constructor.
- If you don't type the constructor, Java will create one for you
- You do not call a constructor. It runs when you use the keyword
new - Constructors do not have return types; they are not methods
- It's common to have a no-argument constructor
- You can also create a constructor that takes parameters
What if I don't create a constructor?
You'll get one anyway. Subclasses receive a default constructor that contains a call to the superclass's constructor. If you don't program this then Java will.
Example 1: Default constructor
public Lawyer() {
super(); // calls Employee() constructor
}
Example 2: A constructor that takes arguments replaces the default constructor.
Employee(int) replaces the default Employee().
The subclasses' default constructors are now trying to call a non-existent default Employee constructor.
super(parameters);
public class Lawyer extends Employee {
public Lawyer(int years) {
super(years); // calls Employee c'tor
}
...
}
Do constructors get inherited?
Constructors are not inherited. If we add a constructor to the Employee class, our subclasses do not compile. The error:
Lawyer.java:2: cannot find symbol
symbol : constructor Employee()
location: class Employee
public class Lawyer extends Employee {
^
The short explanation: Subclasses don't inherit the overridden constructors. Once you write a constructor that requires parameters in the superclass, you must now write constructors for your subclasses as well.
Subclasses don't inherit the Employee(int) constructor.