Isn't this one automatically put by the compiler if I don't put it in a subclass's constructor?
That means I don't even need to care about it? In some articles they put it out.
And if I've got one constructor with arguments, will this be the constructor, or does it take a constructor without argument list?
Firstly some terminology:
So all classes have at least one constructor.
Subclasses constructors may specify as the first thing they do which constructor in the superclass to invoke before executing the code in the subclass's constructor.
If the subclass constructor does not specify which superclass constructor to invoke then the compiler will automatically call the accessible no-args constructor in the superclass.
If the superclass has no no-arg constructor or it isn't accessible then not specifying the superclass constructor to be called (in the subclass constructor) is a compiler error so it must be specified.
For example:
public class Base { }
public class Derived extends Base { }
This is fine because if you add no constructor explicitly Java puts in a public default constructor for you.
public class Base { }
public class Derived extends Base { public Derived(int i) { } }
Also fine.
public class Base { public Base(String s) { } }
public class Derived extends Base { }
The above is a compilation error as Base has no default constructor.
public class Base { private Base() { } }
public class Derived extends Base { }
This is also an error because Base's no-args constructor is private.
If the super class constructor has no arguments Java automatically calls it for you. If it has arguments you'll get an error.
src: http://java.sun.com/docs/books/tutorial/java/IandI/super.html
Calling the no-arguments super constructor is just a waste of screen space and programmer time. The compiler generates exactly the same code, whether you write it or not.
class Explicit() {
Explicit() {
super();
}
}
class Implicit {
Implicit() {
}
}
Update (December 2018):
Writing an explicit super() helps navigating the source code in the IDE.
As of December 2018, neither Eclipse nor IntelliJ provide any means of comfortably navigating from the constructor of the derived class to the constructor of the base class.
Default parent constructor is called from child default constructor even if you do not call it.
Main
public class Main {
public static void main(String[] args) {
A a = new B();
}
}
A
public class A {
public A() {
System.out.println("A");
}
}
B
public class B extends A {
public B() {
System.out.println("B");
}
}
Prints
A
B
Any class constructor always calls "super()" if there is not explicitly called super([arguments]), only we keep in mind access of super class constructor while programming... when we not extends any specific class automatic extends java.lang.Object class
abstract class Book
{
String title;
String author;
Book(String t,String a){
title=t;
author=a;
}
abstract void display();
}
If super class can have a No-args constructor .It is good to have a no argument constructor otherwise you have to pass super constructor with parameter .
If the superclass has no no-arg constructor or it isn't accessible then not specifying the superclass constructor to be called (in the subclass constructor) is a compiler error so it must be specified
class MyBook extends Book{
int price ;
public MyBook(String t,String a,int price){
super(t,a);
this.price=price;
}
public void display(){
System.out.println("Title: "+title);
System.out.println("Author: "+author);
System.out.println("Price: "+price);
}
}
