oops.

 copy constructor - 

package program;

import java.util.*;

class demo{

int a , b;

demo(int a , int b){

this.a=a;

this.b=b;

System.out.println(a+" "+b);

}

demo(demo ref){

a=ref.a;

b=ref.b;

System.out.println(a+" "+b);

}

}

public class code {

    public static void main(String[] args) {

    demo d1 = new demo(10,20);

    demo d2 = new demo(d1);

}

}

private constructor - 

package program;

import java.util.*;

public class code {

int a;

String s;

private code(){

System.out.println(a+" "+s);

}

    public static void main(String[] args) {

    code d1 = new code();

}

}

constructor overloading - 

// Constructor overloading program

package program;

import java.util.*;

public class code {

int a;

String s;

// private constructor

private code(){

System.out.println(a+" "+s);

}

// Parameterized constructor

code(int a , String s){

    this.a=a;

    this.s=s;

    System.out.println(a+" "+s);

}

// Copy constructor

code(code ref){

    a=ref.a;

    s=ref.s;

    System.out.println(a+" "+s);

}

    public static void main(String[] args) {

    code d1 = new code();

    code d2 = new code(10,"ved");

    code d3 = new code(d2);

}

}

private constructor