Is a default constructor automatically provided?

A default constructor is provided automatically if no constructors are explicitly declared in the class. At least one constructor must always be defined explicitly.

Can a default constructor be empty?

As it was said before, if you define any constructor for your class, you have no more (compiler generated no-arg) “default constructor” and in this case if you want to write something like I mentioned above, you should provide your own no-arg constructor.

What happens if you do not supply a default constructor?

If you do not include a constructor, the Java compiler will create a default constructor in the byte code with an empty argument.

Does Java automatically create a default constructor?

Like C++, Java automatically creates default constructor if there is no default or parameterized constructor written by user, and (like C++) the default constructor automatically calls parent default constructor.

Do you always need a default constructor?

@Jos You don’t have to create a default constructor, if you don’t want one. But if you do want one, you’ll have to provide it yourself (or make it = default ).

What is the purpose of default constructor?

Q) What is the purpose of a default constructor? The default constructor is used to provide the default values to the object like 0, null, etc., depending on the type.

When should a default constructor be removed?

Deleting the default constructor of a class is a good idea when there are multiple choices for the default or uninitialised state. For example, suppose I have a class, which represents a polynomial over a field, F .

What is the purpose of a default constructor when must the developer provide the constructor explicitly?

If not Java compiler provides a no-argument, default constructor on your behalf. This is a constructor initializes the variables of the class with their respective default values (i.e. null for objects, 0.0 for float and double, false for boolean, 0 for byte, short, int and, long).

What is a default constructor It is a constructor?

A default constructor is a constructor that either has no parameters, or if it has parameters, all the parameters have default values. The compiler will implicitly define A::A() when the compiler uses this constructor to create an object of type A . The constructor will have no constructor initializer and a null body.

Why do we need a default constructor?

Compiler defined default constructor is required to do certain initialization of class internals. It will not touch the data members or plain old data types (aggregates like an array, structures, etc…). However, the compiler generates code for default constructor based on the situation.

Why do we need an empty constructor?

An empty constructor is needed to create a new instance via reflection by your persistence framework. If you don’t provide any additional constructors with arguments for the class, you don’t need to provide an empty constructor because you get one per default.

What is the difference between default constructor provided by the compiler and a user define constructor?

Default constructor is created only if there are no constructors. If you define any constructor for your class, no default constructor is automatically created. A Default constructor is defined to have no arguments at all as opposed to a constructor in general which can have as many arguments as you wish.

Why C++ compiler does not create default constructor for every class?

In C++, compiler by default creates default constructor for every class. But, if we define our own constructor, compiler doesn’t create the default constructor. This is so because default constructor does not take any argument and if two default constructor are created, it is difficult for the compiler which default constructor should be called.

Is it possible to create an empty constructor for a class?

If you don’t provide any additional constructors with arguments for the class, you don’t need to provide an empty constructor because you get one per default. You can also use the @PersistenceConstructor annotation which looks like following @PersistenceConstructor public Movie(Long id) { this.id = id; }

Is the default constructor always defined in Java?

A default constructor is always declared. But it is not always defined. Only if it is used, then the compiler (or you) define it. Examples: If you always create objects of an class using a constructor with parameters it won’t need the default constructor.

Why does Java always give you an invisible empty constructor?

But java always give you a default invisible empty constructor (if you don’t redefine one). This statement is true only when you don’t provide any constructor in your class. If an argument constructor is provided in your class, then jvm will not add the no-argument constructor.