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When invoking a constructor from subclass its super class's no-arg constructor is always invoked?
Wiki User
∙ 12y ago
Implicitly: (i.e., you do not code for it, but works as if you did)
calling the no-argument constructor of the subclass, and there is no explicitly "redirect" codes.
Explicitly:
a constructor with base() / super() in the implementation, even that invoked constructor required some arguments.
C# example: public SubClass(string whatever) : base() {//...}
Wiki User
∙ 12y ago
Wiki User
∙ 13y agoYes. The invocation to the super class constructor must always be the first line in any class's constructor
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Default constructor in java?
If you don't type a constructor into your class code, a default constructor will be automatically generated by the compiler. The default constructor is ALWAYS a no-arg constructor. (Obviously the compiler has no clue what all arguments you might want for your class. So it takes the safe way out with a no argument constructor) A no-arg constructor is not necessarily the default (i.e., compiler-supplied) constructor, although the default constructor is always a no-arg constructor. The default constructor is the one the compiler provides! While the default constructor is always a no-arg constructor, you're free to put in your own no-arg constructor.
What is the difference between implicit and explicit call of constructor in c plus plus?
An implicit constructor call will always call the default constructor, whereas explicit constructor calls allow to chose the best constructor and passing of arguments into the constructor.
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".
Difference between method and constructor in java?
A constructor is technically a type of method, but it is a very special type. Whereas other methods can be used to do just about anything, the only purpose of a constructor method is to create an instance of the class that contains it, often with parameters passed to it through another part of the program. This instance is called an "object" and is a central part of not only Java, but other object-oriented languages as well. A constructor method always has the same name as its containing class, and does not have a return type. Think of it this way: a class in Java is like a generic blueprint for a house. Your instance variables are like different attributes of the house - how many bathrooms will your house have, what colour will it be? Once you decide on the exact specifications for your house, you can give those parameters to the construction company, which will actually create that house. That's what a constructor method does - takes input parameters (or, lacking them, sets defaults) and creates an object.
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.
Do we need Always need constructor in every class?
Objects are constructed. You can't make a new object without invoking a constructor. In fact, you can't make a new object without invoking not just the constructor of the object's actual class type, but also the constructor of each of its superclasses including the Object class itself! Constructors are the code that runs whenever you use the keyword new.
Default constructor in java?
If you don't type a constructor into your class code, a default constructor will be automatically generated by the compiler. The default constructor is ALWAYS a no-arg constructor. (Obviously the compiler has no clue what all arguments you might want for your class. So it takes the safe way out with a no argument constructor) A no-arg constructor is not necessarily the default (i.e., compiler-supplied) constructor, although the default constructor is always a no-arg constructor. The default constructor is the one the compiler provides! While the default constructor is always a no-arg constructor, you're free to put in your own no-arg constructor.
What is a default parameterized constructor?
There is no such thing as a default parameterized constructor. The default constructor is always the 'no-arg' constructor and does not take any parameters or arguments as input
What is the difference between implicit and explicit call of constructor in c plus plus?
An implicit constructor call will always call the default constructor, whereas explicit constructor calls allow to chose the best constructor and passing of arguments into the constructor.
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".
Difference between method and constructor in java?
A constructor is technically a type of method, but it is a very special type. Whereas other methods can be used to do just about anything, the only purpose of a constructor method is to create an instance of the class that contains it, often with parameters passed to it through another part of the program. This instance is called an "object" and is a central part of not only Java, but other object-oriented languages as well. A constructor method always has the same name as its containing class, and does not have a return type. Think of it this way: a class in Java is like a generic blueprint for a house. Your instance variables are like different attributes of the house - how many bathrooms will your house have, what colour will it be? Once you decide on the exact specifications for your house, you can give those parameters to the construction company, which will actually create that house. That's what a constructor method does - takes input parameters (or, lacking them, sets defaults) and creates an object.
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.
What is the method of constructor overloading?
The first thing to note about constructor overloading is that Java creates a no argument constructor for you if and only if you have not typed a constructor yourself. Every class has a constructor even abstract ones (default no argument constructor). Abstract constructors are always executed. To overload a constructor you can do the following: class Test { String name; Test(String n) { name = n; System.out.println("Constructing Test Object named: " + name); } } In the case above we are overloading the default no argument constructor with a constructor that takes a String parameter. You can write you own no argument constructor as follows: class Test { Test() { System.out.println("Constructing Test Object"); } } To override our own no argument constructor we do this: class Test { Test() { // our no argument constructor System.out.println("Constructing Test Object"); } String name; Test(String n) { // overloading our no argument constructor with this // constructor that take a String parameter name = n; System.out.println("Constructing Test Object named: " + name); } }
What is return data type?
A Constructor in java cannot have a return type. It always creates and returns an object of the class for which it is the constructor. You cannot return a value from a constructor explicitly and if you try to do that, the compiler will give an error. The system knows that the purpose of the constructor is to create an object of the class and it will do the same irrespective of whether you declare a return type or not.
What is the technical name for calling a base class constructor using derived class constructor?
You cannot actually call any constructor, you can only invoke construction, either by instantiating a static instance of a class or by dynamically creating one with the new operator. In the case of base class construction via a derived class, the base class constructor is invoked by the derived class' initialisation list. Every class constructor has an initialisation list whether you define one or not (the compiler will generate one automatically if you don't). When you derive one class from another, the derived class initialisation list invokes a call to the base class default constructor. The only exception is the compiler-generated copy constructor which automatically calls the base class copy constructor. If you define your own initialisation list, then you can explicitly invoke any base class constructor overload, thus making your construction code all the more efficient. However, copy constructors should always invoke the base class copy constructor, so if you define a copy constructor, you must explicitly invoke the base class copy constructor -- the compiler will not invoke it implicitly from a user-defined copy constructor. While many programmer's use the constructor's body to initialise a class, this is highly inefficient. Even if you don't specify an initialisation list, one is created for you, resulting in every base class and every member variable being initialised twice, which can quickly add up to a substantial cost in performance. The constructor's body should only really be used for initialisation when it would be difficult or impossible to do so from the initialisation list. Remember that your object doesn't physically exist until initialisation is complete, so you may not have access to some members, particularly base class members, at certain points in the initialisation process. Initialisation must be done from the ground up, starting with the base classes and ending with the actual class members, and all in the order they were declared. Note that only direct base classes (or virtual base classes) should be invoked from the initialisation list. The base classes themselves should invoke their own base class constructors, if they have any. Thus no matter which derivative you construct, the least-derived class is always constructed first.
What is the difference between default constructor and parameterized constructor?
A default constructor is one that has no parameters (C++ also calls constructors with all default parameters a default constructor), while a parameterized constructor is one that has at least one parameter without a default value. Default constructors can be provided by the compiler if no other constructors are defined for that class or any class the class inherits from, while parameterized constructors must always be defined by the developer.
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(); } }
