Constructor in Java, Rules, Types, and Ways to Create Constructor | 2021

Constructor in Java
Constructor in Java
croe java topics

In this Tutorial we learn about constructor in java, default and Parameterized Constructor in java, Rules and Purpose of a Constructor, Constructor Calling, Difference Between Constructor and Method.

What is constructor in java?

It is one of the members of the class, just like method and variable. And its name must be the same as a class name, and it can not have any return type, not even void. Constructors are executed when we create an object

Rules For The Constructor in Java?

There are three rules to define for the constructor.

  1. The constructor name and class name must be the Same.
  2. It hasn’t any explicit return type, not even void.
  3. Constructors can’t be abstract, final, static, and also synchronized.

Read Also: Top Ways to do Method Overriding In Java?

Types of constructor in java:

These various types of constructors.

  1. Default constructor (no-arg constructor).
  2. Parameterized constructor.
types of constructor in java, types of constructor, how many types of constructor in java

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Default Constructor in Java ?

A default constructor is a select type of constructor. Whenever we create an object using new () keywords. the default constructor is automatically created by the compiler (Not by JVM).

Question:- how to call default constructor from parameterized constructor in java?

default constructor in java, default constructor, what is not true about default constructor,
what is not true about default constructor

Default constructors are used to initialize the resources or instance variables to default values. They do not take any Parameters. And the access modifiers of the default constructor are the same as the class.


Default constructor in java example

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Default constructor in java example, Default constructor

Note:- Why is its name a constructor? The simple answer is because it constructs the values at the time of object creation. When the class does not have any constructor. then the compiler will create a default constructor.

Parameterized Constructor in java?

The programmer or user creates these types of constructors. That’s why we called custom/user-defined or parameterized constructors.

Parameterized Constructor Example:

The primary purpose of a parameterized constructor is to initialize an instance variable to dynamic values or user-defined values at the time of object creation.

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Java Constructor Example.

When Global and Local variables have the same name.

Java Constructor Example.

Note:- These types of Constructors can be parameterized or non parameterized. Only one constructor can be live, parameterized. or default in the class but not Both together.

Use or Purpose of a Constructor?

In simple words, both constructors are used to initialize at the time of object creation. The significant difference between the default and the parameterized constructor. we don’t need to initialize the default constructor because the compiler automatically generates it. Still the parameterized constructor gives an option to make it custom values.

Ways to Call Constructor?

In Java, we have three different ways to call Constructor.

  • With the help of the “new” keyword.
  • Using this() keyword.
  • And using Super() Keyword.

Read Also:- Full Explained Aggregation, Composition, And Association In Java.

Difference Between Constructor and Method?

1They are used to initialize the states of the objectMethods used for exposing the behavior of the class objects.
2A constructor doesn’t have any return type.The method has a return type.
3They are invoking implicitly.They are invoking explicitly.
4When we don’t have in the class, the compiler generates a default constructor.The compiler does not provide the method.
5Make sure the constructor name and class name are the same.Sometimes Method names and the class name are the same or sometimes not.
Constructor and Method differences


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