Constructor in Java || Types of Constructors (Default, No-arg, Parameterized) - In Details

- 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. - In short constructor and method are different. - Constructor has same name as the class and looks like this in a java code. - Note that the constructor name matches with the class name and it doesn’t have a return type. 0:00 - Introduction 05:10 - Default Constructor 05:32 - No-arg Constructor 07:42 - Parameterized Constructor === How does a constructor work === - To understand the working of constructor, lets take an example. lets say we have a class Demo. - When we create the object of Demo like this: Demo d = new Demo() - The new keyword here creates the object of class Demo and invokes the constructor to initialize this newly created object. -Here we have created an object d class Demo and then we displayed the instance variable name of the object. - As you can see that the output is "Learning and Teaching Coding" which is what we have passed to the name during initialization in constructor. - This shows that when we created the object d the constructor got invoked. - - In this example we have used this keyword, which refers to the current object, object d in this example. === Types of Constructors === [1] Default constructor : - If you do not implement any constructor in your class, Java compiler inserts a default constructor into your code on your behalf. - This constructor is known as default constructor. - You would not find it in your source code(the java file) as it would be inserted into the code during compilation and exists in .class file. [2] no-arg constructor : - Constructor with no arguments is known as no-arg constructor. - The signature is same as default constructor, however body can have any code unlike default constructor where the body of the constructor is empty. - Although you may see some people claim that that default and no-arg constructor is same but in fact they are not, even if you write public Demo() { } in your class Demo it cannot be called default constructor since you have written the code of it. [3] Parameterized constructor : - Constructor with arguments(or you can say parameters) is known as Parameterized constructor. - In this example we have a parameterized constructor with two parameters id and name. While creating the objects obj1 and obj2 I have passed two arguments so that this constructor gets invoked after creation of obj1 and obj2. #LearningandTeachingCoding