Java中的默认构造函数？

Question

What is the purpose of the default constructor in java

class Bike1 {
    Bike1() {
        System.out.println("Bike is created");
    }
    public static void main(String args[]){
        Bike1 b=new Bike1();
    }
}

Answer 1

The default constructor provides the default values to the objects. The java compiler creates a default constructor only if there is no constructor in the class.

Answer 2

Your example provides a constructor,

Bike1(){System.out.println("Bike is created");}

which means you do not get a default constructor. A default constructor is inserted if you do not provide any constructor. Finally, Bike1 is a no-args constructor with package level (or default) access permission and appears to display a message when an instance of Bike1 is created.

Answer 3

Default constructor means that when you don't create any constructor for your class, the compiler automatically creates a default constructor (with no parameters) to your class at the time of compilation.

In your example you created a constructor. The constructor does not create any objects, it initialize the object.

Answer 4

Default constructors allow you to create objects with known, default settings and behavior. If you call a constructor with arguments, you are creating a custom object. But calling the default constructor will create objects with identical properties every time it is used.

Typically, a default constructor with "no code" doesn't need any code; it already has all the information it needs to create the object.

Remember that default constructor and a constructor with no-args are different. Since you are defining a constructor Bike1(){} here, the default constructor will loose it's scope and will not be generated automatically.

Answer 5

The default constructor is the no-argument constructor automatically generated unless you define another constructor. It initialises any uninitialised fields to their default values... follow this link.. Java default constructor

Answer 6

Default constructor have no arguments(parameters) and constructor name is same as class name.It will invoke at the time of object creation.

Example:

class Display{

Display(){

System.out.println("Default Constructor");

}

}

class constructor{

public static void main(String args[]){

Display dis=new Display();

}

}

Output:

Default Constructor

Because when the time of object creation default constructor will invoke automatically.