About Java Polymorphism super ()

I have investigated polymorphism again, so I will summarize it. This time I want to deepen and understand super ()

** Target **

--Someone who writes Java somehow

super () is the constructor of the parent class

** Conclusion **

I will try it with a concrete example

Concrete example

`Person.java`


public class Person {
    Person() {
        System.out.println("I am a human." + );
    }
}

`Student.java`


public class Student extends Person {
    Student() {
        System.out.println("I am a student.");
    }
}

`Main.java`


public class Main {
    public static void main() {
        new Student();
    }
}

I am a human.
I am a student.

Commentary

The constructor of the Student class does not have a description to output "Human.", But it is displayed. In other words, the constructor of the Student class that inherits Person

`Person.java`


public class Student extends Person {
    Student() {
        super();
        System.out.println("I am a student.");
    }
}

It looks like this.

(It's not actually done, but if you write it explicitly, it looks like this. When you create an instance of an inherited class, the constructor of the parent class is called automatically)

This super () is the constructor of the parent class.

Add argument

Then add the arguments to the constructor of the parent class

`Person.java`


public class Person {

    private String name;

    Person(String name) {
        this.name = name;
        System.out.println(name + "is.");
    }
}

`Main.java`


public class Main {
    public static void main() {
        new Student();
    }
}

Yes. There is a compilation error. This is because the constructor of the Person class requires an argument. In such a case, you need to call super () with an argument in the Student class.

`Student.java`


public class Student extends Person {
    Student(String name) {
        super(name);
        System.out.println("I am a student.");
    }
}

`Main.java`


public class Main {
    public static void main() {
        new Student("Yamada");
    }
}

This is Yamada.
I am a student.

Student inherits from Person, so it also has a name field

`Main.java`


public class Main {
    public static void main() {
        Student student = new Student("Yamada");
        System.out.println(student.name);
    }
}

This is Yamada.
I am a student.
Yamada