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Java > Learn Java > What exactly the work of constructor( default, parameterized)...
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What exactly the work of constructor( default, parameterized) especially about instance variables initialization. Suppose user initialize the instance variables explicitly. Then what is the use of parameterized constructor over here.. Please reply me

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Constructor is used to initialize an object at the time of creation. A default constructor is provided by the compiler itself if no constructor is provided by the user. It initializes the state of the object to its default values. Parameterized constructor is used to provide values to the object at the...
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Constructor is used to initialize an object at the time of creation. A default constructor is provided by the compiler itself if no constructor is provided by the user. It initializes the state of the object to its default values. Parameterized constructor is used to provide values to the object at the time of creation. If you want to set the values later, after the creation of the object then one can use setter methods to set values. read less
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Software Developer, Expertise in Java/J2ee Technology.

Construct as the name suggest are used to construct the object. So, they are invoked only once and that too at the time of object creation. Default Constructor : Initialize all the instance variables with their default values. Parameterized Constructor : Are used to initialize the instance variables...
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Construct as the name suggest are used to construct the object. So, they are invoked only once and that too at the time of object creation. Default Constructor : Initialize all the instance variables with their default values. Parameterized Constructor : Are used to initialize the instance variables at the time of object creation. 1. There are scenarios where the values of instance variables are known at the time of object creation, so in these scenarios parameterized constructors helps to avoid explicitly initialization of instance variable. 2. There are scenarios where the values of instance variables are not known at the time of object creation, in those scenarios, explicit initialization may be needed on basis of application requirement. read less
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Software Developer, Expertise in Java/J2ee Technology.

Exact work of constructor Or Construction of Object :- It allocates the memory for the object in heap memory. It counts the number of bytes of memory by adding all the instance variable memory sizes. (For eg : int 4 bytes, byte 1 byte etc).
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Constructor is mainly used to access the non static members inside the class by using object and to initialize the class members.
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Senior Software Engineer

Well constructor's is used for object creation and initialization. Yes we can explicitly initialize the instance variable, but as i think it will take one more extra statement to execute. If you are creating one or two objects it is okay, but how about array of objects? So it is good to use Parameterized...
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Well constructor's is used for object creation and initialization. Yes we can explicitly initialize the instance variable, but as i think it will take one more extra statement to execute. If you are creating one or two objects it is okay, but how about array of objects? So it is good to use Parameterized constructor if you want to initialize values while object creation. read less
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Java is primarily an object oriented programming language..that means there will be objects ..objects will have state and behavior..state points to the values of the attributes and the behavior is the methods that we give inside an object..having said that..when make a parameterized constructor we are...
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Java is primarily an object oriented programming language..that means there will be objects ..objects will have state and behavior..state points to the values of the attributes and the behavior is the methods that we give inside an object..having said that..when make a parameterized constructor we are assigning some sort of a default state for that object eg: class Person { private String name; private int age; public Person(String argName,int argAge){ this.name = argName; this.age = argAge } public String toString(){ System.out.println("Name" + this.name); System.out.println("Age"+this.age); } public static void main(String[] args){ Person sidd = new Person("Sidd",29); Person sur = new Person("Sur",21); sidd.toString();//will show Sidd and 29 sur.toString();//will show Sur and 21 } } so here we have 2 objects with two different states..but if we did this then class Person{ String name = "sameNameAlways"; int age = 39; public Person(){ //dont do anything here... } public String toString(){ System.out.println("Name" + this.name); System.out.println("Age"+this.age); } public static void main(String[] args){ Person sidd = new Person(); Person sur = new Person(); sidd.toString();//will show sameNAmeAlways and 39 sur.toString();//will show sameNAmeAlways and 39 } } this will have 2 different objects because we used the new operator but with same states..redundant or not of any use or duplicate objects... read less
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Computer Savvy Professional

A constructor call is more complicated than an ordinary subroutine or function call. It is helpful to understand the exact steps that the computer goes through to execute a constructor call: First, the computer gets a block of unused memory in the heap, large enough to hold an object of the specified...
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A constructor call is more complicated than an ordinary subroutine or function call. It is helpful to understand the exact steps that the computer goes through to execute a constructor call: First, the computer gets a block of unused memory in the heap, large enough to hold an object of the specified type. It initializes the instance variables of the object. If the declaration of an instance variable specifies an initial value, then that value is computed and stored in the instance variable. Otherwise, the default initial value is used. The actual parameters in the constructor, if any, are evaluated, and the values are assigned to the formal parameters of the constructor. The statements in the body of the constructor, if any, are executed. A reference to the object is returned as the value of the constructor call. The end result of this is that you have a reference to a newly constructed object. read less
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ICT provide computer education such as a Engineering,School Subjects, Graphics & Web Design

Here, difference between how to object created.
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Java is primarily an object oriented programming language..that means there will be objects ..objects will have state and behavior..state points to the values of the attributes and the behavior is the methods that we give inside an object..having said that..when make a parameterized constructor we are...
read more
Java is primarily an object oriented programming language..that means there will be objects ..objects will have state and behavior..state points to the values of the attributes and the behavior is the methods that we give inside an object..having said that..when make a parameterized constructor we are assigning some sort of a default state for that object eg: class Person { private String name; private int age; public Person(String argName,int argAge){ this.name = argName; this.age = argAge } public String toString(){ System.out.println("Name" + this.name); System.out.println("Age"+this.age); } public static void main(String[] args){ Person sidd = new Person("Sidd",29); Person sur = new Person("Sur",21); sidd.toString();//will show Sidd and 29 sur.toString();//will show Sur and 21 } } so here we have 2 objects with two different states..but if we did this then class Person{ String name = "sameNameAlways"; int age = 39; public Person(){ //dont do anything here... } public String toString(){ System.out.println("Name" + this.name); System.out.println("Age"+this.age); } public static void main(String[] args){ Person sidd = new Person(); Person sur = new Person(); sidd.toString();//will show sameNAmeAlways and 39 sur.toString();//will show sameNAmeAlways and 39 } } this will have 2 different objects because we used the new operator but with same states..reduntant or not of any use or duplicate objects... read less
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Java Technical Leader

Look to be specific parametrized constructor are useful for populate those instances which are must/or required for a object. If a particular instance vairable value is optional you can set it via setter. It is purly design decision
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