Difference between a no-arg constructor and a default constructor in Java

parameterized constructor in java
zero argument constructor java
non default constructor java
difference between default and parameterized constructor
difference between copy constructor and parameterized constructor
why default constructor is needed in java
constructor and destructor in java
difference between default constructor and copy constructor

Actually I can not understand that what is the difference between a no-arg constructor and a default constructor.

import javax.swing.*;

public class Test extends JFrame {
   public Test() {
     super();
     this.setSize(200,200);
     this.setVisible(true);
   }
   public static void main(Sting[] arg) {
       Test cFrame = new Test();
   }
}

Does this invoke the default constructor of this class while creating Test object called cFrame?


The default constructor is a no-args constructor that the Java compiler inserts on your behalf; it contains a default call to super(); (not supper()) which is the default behavior. If you implement any constructor then you no longer receive a default constructor.

JLS-8.8.9. Default Constructor says (in part),

If a class contains no constructor declarations, then a default constructor with no formal parameters and no throws clause is implicitly declared.

If the class being declared is the primordial class Object, then the default constructor has an empty body. Otherwise, the default constructor simply invokes the superclass constructor with no arguments.

What is the difference between a default constructor and a no-arg , No-argument Constructor in java: As a developer we can create our own constructor with no arguments is known as no-argument constructor. It  Answer to your question is No. Java won't provide a default constructor if you write any kind of constructor in class. One difference between them is that the body of default constructor will always be empty whereas we can insert our own code in no-arg constructor.


The default constructor is a constructor that the Java compiler adds to your code if no explicit constructor is available. The default constructor invokes the super class constructor with no args.

If you have added your own constructor (no matter whether it's without parameters or with parameters) the compiler will not add the default constructor in this case.

Differences between Default constructor and no argument , Default ConstructorA default constructor is a 0 argument constructor which contains a no-argument call to the super class constructor.To assign  A Java developer can choose to explicitlyimplement a no-arguments constructor that is similar to the default constructor (such as accepting no arguments and having no throwsclause). In this post, I


What is a default constructor ?

It is a constructor that is added by the compiler if you have not defined a constructor.

If your class has a constructor already then the compiler will not add the default constructor.

So in your case you have the constructor,

public Test(){
     super();
     this.setSize(200,200);
     this.setVisible(true);
   }

So there is no default constructor now to be invoked by the JVM.

What are the differences between default constructor and , Check out this post to learn more about the difference between the no-arguments constructor and the default constructor in Java. Default Constructor. A default constructor is a 0 argument constructor which contains a no-argument call to the super class constructor. To assign default values to the newly created objects is the main responsibility of default constructor. Compiler writes a default constructor in the code only if the program does not write any constructor in


Answer is No. Reference variable cFrame will call non-arg constructor Test(), not default constructor. While Test() constructor will further find and call non-arg constructor of JFrame class(Parent) and so on Every class must have at least one constructor. If not declared explicitly, java compiler provides a non-parameterised constructor, i.e, default constructor. This default constructor calls its parent class’s non-parameterised constructor It initializes class variables to their default values.

Eg:

Class Base {}

Class Derived extends Base {} // Default constructor of class "Derived" will automatically calls non-arg constructor of class "Base" and intialzes value to the variables

While non-arg constructor is defined by a programmer only. It can also intializes the variables. One more point to add here is that super() call is automatically added by the java compiler, if doesn’t find super() in derived class.

Eg:

Class Base {

int y;
    public Base() {
    }
    public int getY() {
    return y;
    }

}

public class Derived extends Base {
 private int x;

 public Derived() { //super() will be automatically used
 }

 public int getX() {
 return x;
 }

 public void setX(int x) {
 this.x = x;
 }
}

Derived d = new Derived();
 System.out.println("Base x value => " + d.getX());

System.out.println("Base y value => " + d.getY());

Result:

Base x value => 0 // Default value to its primitive datatype(In this case: int)

Base y value => 0

Explicit No-Arguments Constructor Vs. Default Constructor, Almost all Java developers know that compiler adds a default constructor or better known as a no-argument constructor in every Java class, but  A constructor which takes no arguments is known as the default constructor. A constructor which takes one or more arguments is known as parameterized constructor. The compiler inserts a default no-arg constructor after compilation if there is no explicit constructor defined in a class.


Answer to your question is No. Java won't provide a default constructor if you write any kind of constructor in class.

One difference between them is that the body of default constructor will always be empty whereas we can insert our own code in no-arg constructor.

Why Default or No Argument Constructor is Important , No-argument constructor: A constructor that has no parameter is known as default constructor. If we don't define a constructor in a class, then compiler creates  1. A constructor which takes no arguments is known as default constructor. A constructor which takes one or more arguments is known as parameterized constructor. 2. Compiler inserts a default no-arg constructor after compilation, if there is no explicit constructor defined in class.


Constructors in Java, java file) as it is inserted during compilation and present in the bytecode(.class file). default constructor. Are no-arg constructor and default constructor same? This  Difference between the Constructors and Methods Java is a pure OOPS concept based programming language. Hence in Java, all the variables , data and the statements must be present in classes.


Java - Default constructor with example, Types of Constructor. In Java, constructors can be divided into 3 types: No-Arg Constructor; Default Constructor; Parameterized  Default constructor does not have any parameters and is used to set (initialize) class data members. Since, there is no argument used in it, it is called "Zero Argument Constructor". In a class, if there is no default constructors defined, then the compiler inserts a default constructor with an empty body in the class in compiled code.


Java Constructors (With Examples), This is explained in more detail in the section about constructor parameters. Default, no-arg  There are two types of constructors in Java: no-arg constructor, and parameterized constructor. Note: It is called constructor because it constructs the values at the time of object creation. It is not necessary to write a constructor for a class. It is because java compiler creates a default constructor if your class doesn't have any.