Skip to main content

Q) What is a “singleton class” in java? How to make a java class a singleton?




A)
->only one instance of a java class is available throughout the application, that class is known as singleton.

Ex:
//singleton.java
class productDAO
{
private static productDAO dao=new productDAO();------2
privateproductDAO()---------------------------------1
       {
              System.out.println("productDAO class object is created");
       }
public static productDAO getproductDAO()-------------3
       {
              return dao;
       }
}
class singleton {

       public static void main(String[] args) {
              productDAO b1=productDAO.getproductDAO();
              System.out.println(01);
              productDAO b2= productDAO.getproductDAO();
              System.out.println(02);

       }

}

Output:
productDAO class object is created
1
2

Note:
In the above example, productDAO is made singleton. We did the fallowing to make a class singleton.
1)      private accessibility made is given to the contributor of the class.
2)      Created object of the class with in the class itself, its reference is made static.
3)      Through a user defined static method, the object reference is given to the callers.

Additional information:
->whenever constructor declared private that class object can create inside that class only. Any no. of times we can create inside that class, but not in outside of the class.
->so, when the constructor is declared private we prevent the outside object creation of that class.
->once the constructor is declared as private then that class object can’t create outside of that class.
->singleton class should not contain more than one object. I.e. in entire project only one object is created, but anywhere this object reference is used.

Comments

Post a Comment

Popular posts from this blog

Q) What is JDBC driver? What is its role in java database connection?

A) ->A translation software written in java according o JDBC specification is nothing but “JDBC driver”. -> JDBC driver implements JDBC API. Use single API. JDBC driver role: They are 4 roles   1)       Establishing connection between JDBC client and database server. 2)       Receiving JDBC method calls made by JDBC client while performing database (CRUD) operations. 3)       Translating java method calls into DBMS understandable calls and forwarding them to database server. 4)       Receiving the results from database server. Translating them into java format and handling over the same to the JDBC client.
Post a Comment
Read more

Q) What is ODBC?

A) ->open database connectivity is a technology from MS that enables any language program (other than java) to communication with database Management System. ->in java program ODBC is directly not allowed for the fallowing reasons 1) OS dependency 2) Procedural oriented approach 3) Security thread
Post a Comment
Read more

Q) Explain about nested classes?

A) ->defining a class with in another class is known as nesting of the class. Ex: class A {        class B        {                      } //nested class, and inner class.because it is not static class. } //enclosing class or outer class. ->static class is declared in inside an another class then it does not become an inner class. Note: non-static nested class is known as “inner class”. In the above example class B is nested but not an inner class. Ex: class D {        static c        {                      } //nested class, but not an inner class , because of static class. } //outer class. ->we have three different kinds of inner classes. 1) Member inner class 2) Meth...
Post a Comment
Read more