How to create a Singleton Class in java

//  Example of Singleton Pattern in java //

package com.singletondemo;

class SingletonDB {

public static volatile SingletonDB getInstance;

private SingletonDB() {

   if (getInstance != null) {

               throw (new RuntimeException("instance access only 

                            createInstance()"));

    }

}

public static SingletonDB createInstance() {

if (getInstance == null) {

synchronized (SingletonDB.class) {

if (getInstance == null) {

getInstance = new SingletonDB();

}

}

}

return getInstance;

}

}

public class Main {

public static void main(String[] args) {

SingletonDB db = SingletonDB.createInstance();

System.out.println(db);

}

}

How to Insert and Get Data In Mysql Database through ( Prepared Statement ) in java

/*-- Example of Insert Data using Prepared Statement --*/


import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

class DBInsert{

public static void main(String ar[]) throws SQLException{

Connection con = null;
PreparedStatement ps = null;
ResultSet rs = null;

String sender="992003002";
String receiver="Aman Kumar";
String message="Hi testing msg";

try{
Class.forName("com.mysql.jdbc.Driver");

con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test","root","public");
if(con==null){
System.out.println("DataBase Connection Error....");
System.exit(0);
}
else{
System.out.println("DataBase Connected. ");
}

String strQry="Insert into table1(sender,receiver,message)values(?,?,?)";
ps = con.prepareStatement(strQry);
System.out.println("Ready for Insert...");
ps.setString(1,sender);
ps.setString(2,receiver);
ps.setString(3,message);
ps.executeUpdate();
System.out.println("inserted data in DB...");
ps.close();
con.close();
}
catch (SQLException e){
System.out.println(e);
}
catch (ClassNotFoundException e){
System.out.println(e);
}

}
}


/*-- Example of Select (Get) Data using Prepared Statement --*/


import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class DBGet {

public static void main(String args[]) throws SQLException{
Connection con = null;
PreparedStatement ps = null;
ResultSet rs = null;
try{
Class.forName("com.mysql.jdbc.Driver");
con=DriverManager.getConnection("jdbc:mysql://localhost:3306/test","root","public");
if(con==null){
System.out.println("DataBase Connection Error....");
System.exit(0);
}
else{
System.out.println("DataBase Connected. \n");
}

ps=con.prepareStatement("SELECT sender,receiver, message FROM table1");
ResultSet rs1 = ps.executeQuery();
while (rs1.next()){
String sender = rs1.getString(1);
String receiver = rs1.getString(2);
String message = rs1.getString(3);
System.out.println(sender + "\t " + receiver + "\t" + message);
}
}
catch (SQLException e){
System.out.println(e);
} 
catch (ClassNotFoundException e) {
System.out.println(e);
}

}
}