Why do we need copy constructor and when should we use copy constructor in java -

i going through copy constructors, have gone through links in stack on flow , others well. not clear on following points.

1. why need copy constructor
2. when need copy constructor

i mean exact situation or scenario need use copy constructor. can 1 explain example or point out links can go through , understand them in clear.

following links have gone through understanding of copy constructor.

http://www.programmerinterview.com/index.php/java-questions/how-copy-constructors-work/

https://deepeshdarshan.wordpress.com/2013/12/05/copy-constructors-in-java/

the second link explains 'why' , 'where' copy constructor used. still not clear on it.

below class employee.java

package com.test;  /**  * @author avinashd  *  */ public class employee {      private string rollno;     private string name;      //constructor     public employee(string rollno, string name){          this.rollno = rollno;         this.name = name;     }      //copy constructor     public employee(employee employee){      this.rollno = employee.rollno;     this.name = employee.name;      }      public string getrollno() {         return rollno;     }      public void setrollno(string rollno) {         this.rollno = rollno;     }      public string getname() {         return name;     }      public void setname(string name) {         this.name = name;     } } 

copy constructor used create , exact copy of object same values of existing object.

say example have employee values rollno: 1 , name: avinash. copy constructor create similar object values rollno: 1 , name: avinash . both 2 different objects , changes values of on object not affect object.

the question here

when have constructor such

public employee(string rollno, string name){     this.rollno = rollno;     this.name = name; } 

to create object. can call same constructor create object. why need call copy constructor.when need call ?. please explain

there 2 reasons using copy constructor instead of constructor passing parameters :

1. when have complex object many attributes more simpler use copy constructor
2. if add attribute class, change copy constructor take new attribute account instead of changing every occurence of other constructor