What do you mean by constructor in Java?

Asked By: Iakes Stumpferl | Last Updated: 29th April, 2020
Category: technology and computing programming languages
4.5/5 (38 Views . 20 Votes)
Constructor is a block of code that initializes the newly created object. A constructor resembles an instance method in java but it's not a method as it doesn't have a return type. Constructor has same name as the class and looks like this in a java code.

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Keeping this in view, what is a constructor in Java?

A Java constructor is special method that is called when an object is instantiated. In other words, when you use the new keyword. The purpose of a Java constructor is to initializes the newly created object before it is used. This Java constructors tutorial will explore Java constructors in more detail.

Also, how do you define a constructor? A constructor is a special method of a class or structure in object-oriented programming that initializes an object of that type. A constructor is an instance method that usually has the same name as the class, and can be used to set the values of the members of an object, either to default or to user-defined values.

Also Know, what is constructor in Java with example?

Difference between constructor and method in Java

Java Constructor Java Method
A constructor is used to initialize the state of an object. A method is used to expose the behavior of an object.
A constructor must not have a return type. A method must have a return type.

What is the default constructor in Java?

In both Java and C#, a "default constructor" refers to a nullary constructor that is automatically generated by the compiler if no constructors have been defined for the class. A programmer-defined constructor that takes no parameters is also called a default constructor in C#, but not in Java.

38 Related Question Answers Found

Can a constructor be private?

Yes, class can have a private constructor. It is needed as to disallow to access the constructor from other classes and remain it accessible within defined class. A singleton is a design pattern that allows only one instance of your class to be created, and this can be accomplished by using a private constructor.

Why are constructors used?

The purpose of constructor is to initialize the object of a class while the purpose of a method is to perform a task by executing java code. Constructors cannot be abstract, final, static and synchronised while methods can be.

What is constructor and its types?

A constructor is a special type of function with no return type. We define a method inside the class and constructor is also defined inside a class. A constructor is called automatically when we create an object of a class. We can't call a constructor explicitly. Let us see the types of constructor.

How do you constructor?

How to Create Constructors in Java
  1. A constructor doesn't have a return type.
  2. The name of the constructor must be the same as the name of the class.
  3. Unlike methods, constructors are not considered to be members of a class. (That's important only when it comes to inheritance.)
  4. A constructor is called when a new instance of an object is created.

How many constructors can a class have?


You can have 65535 constructors in a class(According to Oracle docs). But IMPORTANTLY keep this in your mind. We achieve this only by CONSTRUCTOR OVERLOADING ( https://beginnersbook.com/2013/05/constructor-overloading/ ). You can create many constructors but with different signatures.

Why constructor has no return type?

So the reason the constructor doesn't return a value is because it's not called directly by your code, it's called by the memory allocation and object initialization code in the runtime. Its return value (if it actually has one when compiled down to machine code) is opaque to the user - therefore, you can't specify it.

What is an interface?

In computing, an interface is a shared boundary across which two or more separate components of a computer system exchange information. The exchange can be between software, computer hardware, peripheral devices, humans, and combinations of these.

Is a constructor a method?

Technically, a constructor usually is a method. New values of an object type are created via constructors. Constructors shall be instance methods, defined via a special form of method contract, which defines the method contract as a constructor for a particular object type.

What is string in Java?

String is a sequence of characters, for e.g. “Hello” is a string of 5 characters. In java, string is an immutable object which means it is constant and can cannot be changed once it has been created.

What is super keyword in Java?


super is a keyword. It is used inside a sub-class method definition to call a method defined in the super class. Private methods of the super-class cannot be called. Only public and protected methods can be called by the super keyword. It is also used by class constructors to invoke constructors of its parent class.

What is parameterized constructor?

A constructor having a specific number of parameters(arguments) is called a parameterized constructor. The parameterized constructor is used to provide different values to the objects, you can also provide the same values.

What is return type in Java?

Return type in Java. In Java, Return is a keyword which is used to exit from the method only with or without a value. Return type may be a primitive type like int, float, double, a reference type, or void type which represents "return nothing". i.e, they don't give anything back.

What is overloading in Java?

Method Overloading is a feature that allows a class to have more than one method having the same name, if their argument lists are different. It is similar to constructor overloading in Java, that allows a class to have more than one constructor having different argument lists.

What are methods in Java?

A Java method is a collection of statements that are grouped together to perform an operation. Now you will learn how to create your own methods with or without return values, invoke a method with or without parameters, and apply method abstraction in the program design.

What is static in Java?


In Java, a static member is a member of a class that isn't associated with an instance of a class. Instead, the member belongs to the class itself. As a result, you can access the static member without first creating a class instance. The value of a static field is the same across all instances of the class.

What is this keyword in Java?

Keyword THIS is a reference variable in Java that refers to the current object. The various usages of 'THIS' keyword in Java are as follows: It can be used to refer instance variable of current class. It can be used to invoke or initiate current class constructor. It can be passed as an argument in the method call.

What is Polymorphism in Java?

Polymorphism in Java is a concept by which we can perform a single action in different ways. We can perform polymorphism in java by method overloading and method overriding. If you overload a static method in Java, it is the example of compile time polymorphism. Here, we will focus on runtime polymorphism in java.