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A constructor is a method that is invoked when an object is created. As to being mandatory, that really depends on the programming language; in the case of Java, each class must have a constructor, however, in many cases Java will automatically provide a default constructor, so you don't really need to program it.
What else can I help you with?
Why do you need a constructor as a class member?
A constructor is not a mandatory member that we need to code specifically for a class. While creating a class, even if we miss out coding the constructor, Java would create a default constructor all by itself. The constructor is usually the place where we initialize things that are required by the class. Hence it is a good practice to code the constructor for our class. Tip: If you do not want anyone to instantiate your class, you can declare the constructor as private. In that way no other class can instantiate your class.
Which situation constructor is used?
Constructor is necessary when you are about to use instance of a class.
What is a constructoris it mandatory to use constructor in a class?
You always should define default constructor for your class. You must also define a copy constructor for your class if there are any pointers in the class. While it is not mandatory, failure to provide a default constructor can result in bad behavior, and failure to provide a copy constructor when you have pointers in the class will result in bad behavior. For example, without a default constructor, the compiler will not fully initialize the attributes of the class. It will initialize the virtual function table, and call base class constructors, but that is all - the attributes could be random garbage. For another example, without a copy constructor, the compiler will generate one that simply makes a bit wise copy of the attributes. If these attributes contain pointers, then you have two pointers to the same object, not necessarily a good thing, especially if one of them get "deleted".
Why you use constructor instead of function?
For every class an empty constructor will be defined automatically by default unless you provide a constructor definition manually. Constructor in a class can be used to initialize variables or perfrom some basic functionallity whenever an object is created.
Why Java always provides a default constructor to class when you use another constructor default constructor remove?
Classes in Java inherit constructors from their parent classes. If you don't explicitly define a parent class, then Object is used, which has only the default empty constructor. That "default" constructor is only there when defined by the parent class, so classes which do not have a no-argument constructor will not allow subclasses to automatically use it. This is implemented this way because of the special nature of constructors. Java could not always provide a default constructor because it could not guarantee that all class members would be properly created or initialized.
Is it mandatory to use the construtors in a class in c plus plus?
No. If you do not provide a default constructor, the compiler will provide a default constructor that simply allocates memory for the class, but it will not initialize the members of the class. If you do not provide a copy constructor, then the compiler will provide a copy constructor that allocates memory for the class, and then copies the member's data from class to class. This is bad if the class contains pointers, because only the pointer will be copied - the objects to which the pointers point will not be copied - and you could wind up deleting an object and then using it after deletion, with potentially devastating consequences. So, yes, it is mandatory, from a good practices point of view, and just plain mandatory when the class has pointers, to always provide a default constructor and a copy constructor, along with the appropriate destructor.
Why do you need a constructor as a class member?
A constructor is not a mandatory member that we need to code specifically for a class. While creating a class, even if we miss out coding the constructor, Java would create a default constructor all by itself. The constructor is usually the place where we initialize things that are required by the class. Hence it is a good practice to code the constructor for our class. Tip: If you do not want anyone to instantiate your class, you can declare the constructor as private. In that way no other class can instantiate your class.
Which situation constructor is used?
Constructor is necessary when you are about to use instance of a class.
What is a constructoris it mandatory to use constructor in a class?
You always should define default constructor for your class. You must also define a copy constructor for your class if there are any pointers in the class. While it is not mandatory, failure to provide a default constructor can result in bad behavior, and failure to provide a copy constructor when you have pointers in the class will result in bad behavior. For example, without a default constructor, the compiler will not fully initialize the attributes of the class. It will initialize the virtual function table, and call base class constructors, but that is all - the attributes could be random garbage. For another example, without a copy constructor, the compiler will generate one that simply makes a bit wise copy of the attributes. If these attributes contain pointers, then you have two pointers to the same object, not necessarily a good thing, especially if one of them get "deleted".
What happens when no constructor function is declared in a class - in Java?
When any constructor is deffined in your class, the java compiler create a default no argument constructor for you. This constructor only have an invocation to the super class constructor (" super( ) ").
Why you use constructors?
To create an instance of the class that implementing that constructor
Why you use constructor instead of function?
For every class an empty constructor will be defined automatically by default unless you provide a constructor definition manually. Constructor in a class can be used to initialize variables or perfrom some basic functionallity whenever an object is created.
Why Java always provides a default constructor to class when you use another constructor default constructor remove?
Classes in Java inherit constructors from their parent classes. If you don't explicitly define a parent class, then Object is used, which has only the default empty constructor. That "default" constructor is only there when defined by the parent class, so classes which do not have a no-argument constructor will not allow subclasses to automatically use it. This is implemented this way because of the special nature of constructors. Java could not always provide a default constructor because it could not guarantee that all class members would be properly created or initialized.
Why base class constructor is first invoked in subclass constructor?
The base class constructor is invoked first when a subclass is instantiated, because the base class must be viable and consistent before the subclass constructor is fired.
How can you recognize a constructor in a class?
A class's constructor will have the same name of the class and no return type (not even void): class Example(){ Example() {printf("This is the constructor\n");} ~Example(){printf("This is the destructor\n");} };
How do you call an abstract class from main method?
An abstract class cannot have a constructor and hence you cannot invoke the constructor of the class - i.e., you can instantiate an abstract class and hence you cannot call the constructor of an abstract class.
How do you get a default constructor?
The default constructor is an empty (only call the super constructor) with no parameters constructor inserted by the java compiler when you don't define a constructor in your class. If you write something like this: public class NoConstructorClass{ //no constructor goes here } Then you get something like this: public class NoConstructorClass{ public NoConstructorClass(){ // Default constructor that you didn't write super(); } }
