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Mastering Constructors in Java: Types and Examples

The constructor in Java is known as the member function of a certain class that gets invoked when the object of the class gets made. In this post, you will get a clear understanding of the constructor in Java, its importance, types, and examples.

You will also gain a detailed understanding of the uses, challenges, and variety of other things. So, let’s begin.

What are Constructors in Java?

The constructor in Java is known as a block of code that constructs the value and state during the object creation. It’s called every time when an object is made with a new keyword. Even when you don’t specify any constructor present in the code, Java will call in a default constructor. This “default constructor” will assign all the default values and states, such as null, 0, and many more, to the object.

Why Constructor in Java is Important?

The constructor in Java is vital because it helps in initializing the objects of the class with the initial values.

Once you know ‘what is constructor in Java’, you will also understand that these constructors get automatically invoked when the objects get made.

When a constructor is not declared for the class, the C++ compiler will generate the default constructor.

Types of Constructors in Java

There are various types of constructors in Java are:

  • No-Argument Constructor
  • Parameterized Constructor
  • Default Constructor 

let’s learn about them in a detailed manner.

1. No-Argument Constructor

The no-argument constructors are pretty in the class. It also comes with a constructor definition without parameters or arguments. They receive the call when an object present in the class is created.

These are types of constructors in Java that declare the variables for all the other member functions. To understand this constructor well, here is an illustration:

class Rectangle
{
 double length;
double breath;
 
Rectangle()
{
 length = 15.5;
breath = 10.67;
}
 double calculatedArea()
{return length*breath}
}
class Rectangle_Main {
  public static void main(String[] args) {
          double area;
          Rectangle myrec = new Rectangle ();
          area = myrec.calculatedArea();
          System.out.printIn(“The area of the Rectangle:” +area);
   }
}
Output: The area of the Rectangle is 165.385

2. Parameterized Constructor

These types of constructors in Java contain parameters in the constructor declaration and definition. You can easily pass over one argument through the parameterized constructor.

To have a better understanding of this constructor in Java, here is an example:

class Square
{
double length;
double breadth;
Rectangle()
{
  length = 10;
 breadth = 20;
}
Rectangle(double l, double b)
{
  length = l;
 breadth = b;
}
double calculatedArea()
{return length*breadth;}
}
class Rectangle_Main {
  public static void main(String[] args) {
          double area;
Rectangle myrec = new Rectangle (41,56)
area = myrec.calculateArea()
System.out.println(“The area of the Rectangle: “+area);
   }
}
Output: The area of the rectangle is 2296.0

3. Default Constructor

The default constructor in Java gets created automatically during the time of object creation when no constructor gets declared in the class. This is a type of constructor that you will not find in the program.

It is created without declaration and definition automatically in the class. To have a good understanding of it, here is an example of java contructor:

class Rectangle
{
double length = 10;
double breadth = 30;
 
double calculateArea()
{return length*breadth;}
}
class Rectangle_Main {
  public static void main(String[] args) {
  double area;
//object creation makes the default constructor in Java without the visible construct description
          Rectangle myrec = new Rectangle();
          area = myrec.calculatedArea();
          System.out,println(“The area of the Rectangle: “ +area);
}
The Output: The area of the rectangle is 300.0

What is Default Constructor in Java

The constructor in Java utilized for initializing the instance variables with the default values is known as the default constructor. These types of constructors in Java do not have any parameters.

The compiler makes the default constructor in Java for the class when you don’t get it done on your own. When you write the constructor with parameters or no parameters, the compiler will not make a default constructor.

When a constructor doesn’t get defined in the program, the compiler automatically makes a constructor by itself.

When an object of a specific class is made, it utilizes the constructor to initialize the variables with all the default values.

Constructor Overloading in Java

The constructor overloading in Java is done when one constructor that has a different type of parameter list can easily reside in a specific class. Every constructor in Java conducts a different task.

They get differentiated by a compiler through a number of parameters under the argument list and also their types.

Parameterized Constructor in Java

The parameterized constructor in Java is a type of constructor that can easily take arguments in the form of inputs.
Mastering Constructors in Java: Types and Examples
When the object is declared in this type of constructor in Java, the initial values get passed to the constructor as arguments. The normal way might not work.

The constructors are called implicitly and explicitly. If you call the method explicitly, then you can also call it a shorthand function.

Use of Constructor in Java

By now, you already know what a constructor is in Java, but do you know it has several uses? Let’s find out!

1. Initialize the Object

The constructor in Java is mainly utilized for initializing the object with the initial or default state. The default value is for the primitives and might not be what you need.

2. Informs About Dependencies

Another use of constructor in Java is that it can inform about all the dependencies. In simple words, with the help of the constructor, you can request a user of a particular class for the dependencies.

Rules for Creating Java Constructor

Before using the constructor in Java, it’s important to keep in mind the rules for creating them. These rules are:

  • The constructor of a certain class should have the same name as the class it resides in.
  • The constructor in Java cannot be synchronized, static, final, or abstract.
  • To control the access of constructor declaration, the access modifiers can be used.

Java Constructor Example

Once you can gain a good understanding of ‘what is constructors in Java,’ it becomes clear how exactly it’s used and what’s the reason behind their usage.

But in this section, a Java constructor example will provide you with a detailed understanding.

“ class Circle {
     private String name;
// constructor
Circle ()
  System.out.println(“Constructor Called:”);
  Name = “Programiz” ;
}
   public static void main(String[] args) {
       //constructor get invoked when
       //making an object of the Main Class
    Main obj = new Main ();
       System.out.println( “The name is” + obj.name);
   }
}
Output: The constructor is known as Programiz

In this Java constructor example, a constructor called “Circle” is made, and inside that constructor, the value of the name variable gets initialized.

Difference Between Constructor and Method in Java

Image Source:

Now that we have understood what is a constructor in java, let’s look at the difference between java constructor and methods. This table will provide you with a clear understanding:

Constructor Method
A constructor’s name remains the same as the class it resides in The constructor’s name can be different from the class
There is no return type in a constructor Method needs to have return type
The constructor in Java gets involved implicitly by the system Methods get invoked explicitly by the programmer
The constructors get executed when the objects are created Methods get executed when you call it explicitly.

 

Challenges Faced

Just like there are Advantages and Disadvantages of Arrays in C, C++, and Java, you will also find several benefits and challenges in Java constructors. Now that we have understood what is java constructors and how they works, let’s comprehend the challenges, which are there:

  • Constructors might not return any value.
  • The constructor is always public. This means when a class is created, the constructor will call it automatically.
  • It’s not possible to inherit the constructor.

Conclusion

The article provides a detailed explanation of what is Java constructors, their types, uses, etc. Make sure to go through all the points to have a good understanding of them.

FAQ's

The constructors in Java are known as a block of code that constructs the value and state during the object creation.
There are 3 different types of constructors in Java:
  • No-Argument Constructor
  • Parameterized Constructor
  • Default Constructor
In short, yes, you can. But you have to be careful when doing it. The compiler will provide a no-parameter default constructor automatically when there is no constructor.
No, you cannot override a constructor.
You can use the constructors to set the initial state of a specific object that contains the initial values for the instance variables.
Yes, you can declare the constructor as private. Declaring a constructor as private means you don’t want to create an object of a specific class.
The constructors manipulate and make objects in Java by creating an instance of a class, which is known as instantiating a class.

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