Skip to main content

Auto boxing

In java every primitive type has its wrapper class. You can store the value in both forms. You can use the object of the wrapper class to hold the value or you can use the primitive type variable. To do this you have to create the object manually and the value is passed to the constructor. If you want to get the value stored in the wrapper class then you have to call the parser method to convert into primitive type.


For example

Integer in=new Integer(234);

int a=in.intValue();

But now you don’t need to bother about conversion. Compiler has the feature through which it makes the automatic conversion between primitive types and its corresponding wrapper classes. So automatically storing the primitive types value into object of corresponding wrapper class is class the auto-boxing and automatically retrieval of value into primitive type form object of corresponding wrapper class is called un-boxing. There following difference between old and new way to conversation.

With Autoboxing
Without Autoboxing
int i;
Integer j;
i = 1;
j = 2;
i = j;
j = i;
int i;
Integer j;
i = 1;
j = new Integer(2);
i = j.intValue();
j = new Integer(i);

public class AutoBoxing
{
    public static void main(String ar[])
    {
        int a=100;
        Integer in=new Integer(200);
        //unboxing value 200
        int b=in;
        //autoboxing value of a
        Integer in2=new Integer(a);
        int c=in2;
        System.out.println(a+b+c);
    }
}

Comments

Popular posts from this blog

Using HyperSQL (HSQLDB)

HSQLDB is a portable RDBMS implemented in pure java. It can be embedded with your application as well as can be used separately. It is very a small database that supports almost all features of the standard database system. It comes with small jar file that can be found in lib folder. The HSQLDB jar package is located in the /lib directory of the ZIP package and contains several components and programs. Core components of jar file are : HyperSQL RDBMS Engine (HSQLDB), HyperSQL JDBC Driver, Database Manager, and Sql Tool. Installing and Using Download: download latest release of HyperSQL database from http://hsqldb.org website and extract it. You will see following contents. Here "bin" directory contains some batch files those can be used to run a swing based GUI tool. You can use runManagerSwing.bat to connect to database, but database must be on before running it. Directory lib contains File hsqldb.jar . It is the database to be used by you. Running database First

In Process Mode of HSQLDB in web application.

If you want to use the database into your web application, you can use the HSQLDB in In_Process mode. In this mode, you can embed the HSQLDB into your web application and it runs as a part of your web application programm in the same JVM. In this mode, the database does not open any port to connect to the application on the hosing machine and you don't need to configure anything to access it. Database is not expposed to other application and can not be accessed from any dabase tools like dbVisualizer etc. In this mode ,database will be unknown from any other person except you. But in the 1.8.0 version, you can use Server intance for external as well as in process access.  To close the databse, you can issue SHUTDOWN command as an SQL query.   In the in-process mode, database starts from JDBC with the associated databse file provided through  connection URL. for example   DriverManager.getConnection("jdbc:hsqldb:mydatabase","SA","");   Here myd

Write a code for servlet which will display all the fields of Employee table in tabular form.MCS-051,Dec09-3a

import javax.servlet.*; import java.io.*; import java.sql.*;   import javax.servlet.http.*;   public class Employee extends HttpServlet   {   public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException,      ServletException   {   res.setContentType("text/Html");   PrintWriter pw = res.getWriter();   try   {   Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");   Connection con=DriverManager.getConnection("jdbc:odbc:dsn");   Statement st=con.createStatement();   ResultSet rs=st.executeQuery("select emp_id,emp_name,emp_dob,mob_no,email from employee");   String tr="";   while(rs.next()){   tr=tr+"<tr>";   tr=tr+"<td>"+rs.getString(1)+"</td>";   tr=tr+"<td>"+rs.getString(2)+"</td>";   tr=tr+"<td>"+rs.getString(3)+"</td>";   tr=tr+"<td>"+rs.getString(4)+"</td>&