[Java] Constructor_2

Constructor_2

- Constructor is a special type of method that is used to initialize the object

- Constructor is invoked at the time of object creation

1. Rule

1) Constructor name must be same as its class name

2) Constructor must have no explicit return type

2. Type of constructor

1) Default constructor

2) Parameterized constructor

3. Default Constructor

3_1. Example

public class DefaultConstructor { public DefaultConstructor(){ System.out.println("Default"); } public static void main(String a[]){ DefaultConstructor defaultConstructor = new DefaultConstructor(); } }

- If there is no constructor in a class, compiler automatically creates a default constructor

3_2. What is the purpose of default constructor?

- Default constructor provides the default values to the object like 0, null, etc

package constructor; public class DefaultConstructor { int id; String name; void display(){ System.out.println(id+" "+name); } public static void main(String a[]){ DefaultConstructor defaultConstructor = new DefaultConstructor(); defaultConstructor.display(); } }  

4. Parameterized Constructor

4_1. Why use parameterized constructor?

- Parameterized constructor is used to provide different values to the distinct objects

package constructor; public class Overloading { public Overloading(int i, String j){ System.out.println("Inside double paramter constructor"); } public static void main(String a[]){ Overloading doubleV = new Overloading(1,"test"); } }  

5. Copy Constructor

- There are many ways to copy the values of one object into another in java

1) By constructor

2) By assigning the values of one object into another

3) By clone() method of Object class

5_1. Example

package constructor; public class copy { int id; String name; public copy(int i, String n){ id = i; name = n; } public copy(copy c){ id=c.id; name=c.name; } void display(){ System.out.println(id+" "+name); } public static void main(String[]args){ copy s1 = new copy(111,"kyle"); copy s2 = new copy(s1); s2.display(); } }