JAVA构造器（Constructor)

JAVA Constructor|JAVA Point

本来想在JAVA对象和类中穿插着复习一下constructor,没想到复习着发现东西越来越多，为了避免一篇文章过于杂乱冗长，于是另写一篇关于constructor构造器的博客。

Defination:
In Java, a constructor is a block of codes similar to the method. It is called when an instance of the class is created. At the time of calling constructor, memory for the object is allocated in the memory.

1. It is a special type of method which is used to initialize the object.
2. Every time an object is created using the new() keyword, at least one constructor is called.
3. It calls a default constructor if there is no constructor available in the class. In such case, Java compiler provides a default constructor by default.
4. There are two types of constructors in Java: no-arg constructor, and parameterized constructor. JAVA中存在两种构造器

Note: It is called constructor because it constructs the values at the time of object creation. It is not necessary to write a constructor for a class. It is because java compiler creates a default constructor if your class doesn't have any.

There are three rules defined for the constructor.

1. Constructor name must be the same as its class name
2. A Constructor must have no explicit return type
3. A Java constructor cannot be abstract, static, final, and synchronized

Example of default Constructor:

//Java Program to create and call a default constructor  
class Bike1{  
//creating a default constructor  
Bike1(){System.out.println("Bike is created");}  
//main method  
public static void main(String args[]){  
//calling a default constructor  
Bike1 b=new Bike1();   //constructor
}  
}  

What is the purpose of the non-param/default constructor?
The default constructor is used to provide the default values to the object like 0, null, etc., depending on the type.

Example of parameterized constructor

class Student4{  
    int id;  
    String name;  
    //creating a parameterized constructor  
    Student4(int i,String n){  
    id = i;  
    name = n;  
    }  
    //method to display the values  
    void display(){System.out.println(id+" "+name);}  
   
    public static void main(String args[]){  
    //creating objects and passing values  
    Student4 s1 = new Student4(111,"Karan");  
    Student4 s2 = new Student4(222,"Aryan");  
    //calling method to display the values of object  
    s1.display();  
    s2.display();  
   }  
}  

Why use the parameterized constructor?
The parameterized constructor is used to provide different values to distinct objects. However, you can provide the same values also.

The difference between Constructor and Method