Constructors in java

 Java Constructors

• Constructor is nothing but a method with a class name
• It doesn't return any values 
• We don't write any return type of the constructor
• It is used to initialise the values when the object is created
• In java there is constructor called default constructor it is automatically initialize when there is no constructor is assigned
• We can also give parameters in the constructor so at the time of initialize we can assign some value into the class. It is known as parametric construction
• If we create a any constructor in a class then the default constructor will not work so we need to write the default constructor also if we want to use them

Ex:

1) Default constructor

class Hello{

public int a=10;

public int b=20;

}

class Hel{

public static void main (String []args){

Hello h=new Hello();// using default constructor 

System.out.print(h.a+h.b);//1020

}

2) Constructor with no parameters 

class Hello{

public Hello(){

System.out.print("Hello");

}

}

class Hel{

public static void main (String []args){

Hello h=new Hello();// calling constructor 

//Output:Hello

}

}

3)Constructor with parameters 

class Hello{

public int num;

public Hello(int num){

this.num=num;

}

}

class Hel{

public static void main (String []args){

Hello h=new Hello(10);// calling constructor with parameters

System.out.print(h.num);//10

// If we try to call the default constructor then it will raise an error

Hello d=new Hello()// error, since there is no default constructor available after we create a own construction 

}

}

4) Creating 2 or more constructors 

class Hello{

public int num=10;

public Hello(int num){

this.num=num;

}

public Hello(){}

}

class Hel{

public static void main (String []args){

Hello h=new Hello(60);// calling constructor with parameters

System.out.print(h.num);//60

Hello d=new Hello();

System.out.print(d.num);//10

}

}