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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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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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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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Java/J2ee,Hibernate,Spring,Oracle,webservices Trainer

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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Sun Certified Java Professional

Suppose your program is as follows class ABC{ int x; ABC(){ x=10; } } After compilation it becomes as follows: class ABC extends java.lang.Object{ int x; ABC(){ //data member is initialized by default value x=0; // now you statement is copied x=10; ...
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Suppose your program is as follows class ABC{ int x; ABC(){ x=10; } } After compilation it becomes as follows: class ABC extends java.lang.Object{ int x; ABC(){ //data member is initialized by default value x=0; // now you statement is copied x=10; } } That is either you initialize your data or not, the constructor will do initialization of instance variable by its default value. 0 for int, 0.0f for float, 0.0 for double type, null for any Object type like String. Parameterized constructor is used to pass some value to set into data member just at the time of creating instance/object of a class. read less
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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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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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Constructor in java is a special type of method that is used to initialize the object. Java constructor is invoked at the time of object creation. It constructs the values i.e. provides data for the object that is why it is known as constructor. Rules for creating java constructor There are...
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Constructor in java is a special type of method that is used to initialize the object. Java constructor is invoked at the time of object creation. It constructs the values i.e. provides data for the object that is why it is known as constructor. Rules for creating java constructor There are basically two rules defined for the constructor. Constructor name must be same as its class name Constructor must have no explicit return type Types of java constructors There are two types of constructors: Default constructor (no-arg constructor) Parameterized constructor read less
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