Constructor

Constructor is a special member function, these are used to initialize the values of objects. When we create an object using the new() keyword atleast one constructor will be executed to assign initial values to that object.

Example

public class Example {
	int a;
	public Example () {
		a = 10;
	}
	public static void main (String[] args) {
		Example ob = new Example();
		System.out.println(ob.a); //prints 10
	}
}

Rules for creating a constructor

• Constructors of a class must have same name as the class in which it is created
• Constructor in java cannot be abstract, final and static.
• Constructors don't have a return type.

Types of constructors

There are 2 types of constructors in java

• Default constructor
• Parameterized constructor

1. Default constructor

• It has 0 parameters
• If we don't create a constructor then the compiler itself creates a default constructor
• If we create atleast one constructor, then the compiler won't do it for us

Example

class Example {
	public Example () {
		System.out.println("constructor created"); // output: constructor created
	}
	public static void main (String[] args){
		Example ob = new Example ();
	}
}

2. Parameterized Constructor

• It has more than 0 parameters
• Used to provide different values to different objects

Example

class Example {
	int a,b;
	public Example (int x, int y) {
		a = x;
		b = y;
	}
	public void add () {
		System.out.println(a+b);
	}
	public static void main (String[] args){
		Example ob = new Example (2,3); // output: 5
		ob.add();
	}
}

Constructor overloading

If we use more than 1 constructor in a class, then it is said to be constructor overloading.

class Example {
	int a,b,c;
	public Example (int x) {
		a = x;
	}
	public Example (int y, int z) {
		b = y;
		c = z;
	}
	public void add () {
		System.out.println(a+b+c);
	}
	public static void main (String[] args){
		Example ob1 = new Example (20,30);
		Example ob2 = new Example (5);
		ob1.add(); 
		ob2.add(); 
	}
}

check output here