Insert data into mysql database using java and netbeans

import java.sql.*;
import java.lang.*;
import java.beans.Statement;
import java.sql.Connection;
import java.sql.DriverManager;
import javax.swing.JOptionPane;

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

/**
 *
 * @author KA
 */
public class contact_list extends javax.swing.JFrame {

    /**
     * Creates new form contact_list
     */
    public contact_list() {
        initComponents();
    }

    /**
     * This method is called from within the constructor to initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is always
     * regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                        
    private void initComponents() {

        jLabel1 = new javax.swing.JLabel();
        jLabel2 = new javax.swing.JLabel();
        jLabel3 = new javax.swing.JLabel();
        jTextField1 = new javax.swing.JTextField();
        jTextField2 = new javax.swing.JTextField();
        jTextField3 = new javax.swing.JTextField();
        jButton1 = new javax.swing.JButton();
        jButton2 = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jLabel1.setText("Name");

        jLabel2.setText("Mobile");

        jLabel3.setText("email");

        jTextField3.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jTextField3ActionPerformed(evt);
            }
        });

        jButton1.setText("Add Contact");
        jButton1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton1ActionPerformed(evt);
            }
        });

        jButton2.setText("Exit");
        jButton2.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton2ActionPerformed(evt);
            }
        });

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createSequentialGroup()
                        .addGap(37, 37, 37)
                        .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                            .addComponent(jLabel1)
                            .addComponent(jLabel2)
                            .addComponent(jLabel3)))
                    .addGroup(layout.createSequentialGroup()
                        .addGap(28, 28, 28)
                        .addComponent(jButton1)))
                .addGap(63, 63, 63)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
                        .addComponent(jButton2)
                        .addComponent(jTextField2)
                        .addComponent(jTextField1))
                    .addComponent(jTextField3, javax.swing.GroupLayout.PREFERRED_SIZE, 101, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addContainerGap(115, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(46, 46, 46)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jLabel1)
                    .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addGap(25, 25, 25)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jLabel2)
                    .addComponent(jTextField2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addGap(21, 21, 21)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jLabel3)
                    .addComponent(jTextField3, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addGap(30, 30, 30)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jButton1)
                    .addComponent(jButton2))
                .addContainerGap(95, Short.MAX_VALUE))
        );

        pack();
    }// </editor-fold>                      

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                        
        // TODO add your handling code here:
         String Name=jTextField1.getText();
        String Mobile=jTextField2.getText();
        String Email=jTextField3.getText();
       
         String emailregex = "^[_A-Za-z0-9-]+(\\.[_A-Za-z0-9-]+)*@[A-Za-z0-9-]+(\\.[A-Za-z0-9-]+)*(\\.[A-Za-z]{2,})$";
         String mobileregex = "^[_0-9-]+(\\.[_A-Za-z0-9-]+)*@[A-Za-z0-9-]+(\\.[A-Za-z0-9-]+)*(\\.[A-Za-z]{2,})$";
         Boolean b = Email.matches(emailregex);
       
        if (Name.isEmpty())
            JOptionPane.showMessageDialog(this,"Name not Entered");
         else if (Mobile.isEmpty())
            JOptionPane.showMessageDialog(this,"Mobile not Entered");
         else if (Email.isEmpty())
            JOptionPane.showMessageDialog(this,"Email not Entered");
         else if(b == false)
         {
               JOptionPane.showMessageDialog(this,"Email Address is Invalid");
         }
       
        else
         {
                try
                   {
                        Class.forName("java.sql.DriverManager");
                        Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/cbse","root","root");
                        String query="INSERT INTO Contact VALUES('"+Name+"','"+Mobile+"','"+Email+"');";
                         PreparedStatement pst = con.prepareStatement(query);
                         pst.executeUpdate(query);

                    }
                    catch(Exception e)
                    //this block is executed in case of an exception
                    {
                    //Display an error message in the dialog box for an exception
                    JOptionPane.showMessageDialog (this, e.getMessage());
                    }
         }
    }                                      

    private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {                                        
        // TODO add your handling code here:
        System.exit(0);
    }                                      

 
    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(contact_list.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(contact_list.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(contact_list.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(contact_list.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new contact_list().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                    
    private javax.swing.JButton jButton1;
    private javax.swing.JButton jButton2;
    private javax.swing.JLabel jLabel1;
    private javax.swing.JLabel jLabel2;
    private javax.swing.JLabel jLabel3;
    private javax.swing.JTextField jTextField1;
    private javax.swing.JTextField jTextField2;
    private javax.swing.JTextField jTextField3;
    // End of variables declaration                  
}

Meaning for public static void main () in java

Meaning for public static void main () in java

public  is a modifier indicates that method can be used by other java clases

static  is a modifier indicates that main() doesn’t require any object to access the method

void -no value is returned

main() -flow control is given to main().Execution order is depend on this instruction order  in the main() function

Class Key Words And Identifiers In Java

public class Display{

public is a keyword which means means what we are named can use by other classes

class is a keyword which indicates a class is being named

Display is an identifier gives the name of the class

{   Opening braces delimiter  indicates description of class members 

Java on internet

Java on internet

Write a program to reverse a string

import java.util.*;

 class ReverseAString           //class name

{

   public static void main(String args[])  //main function

   {

      String original, reverse = "";    //string declaration

      Scanner in = new Scanner(System.in);                //to get input from- //-user

      System.out.println("Enter a string to reverse"); //Ask //string to reverse from user

original = in.nextLine();                            //getting input from user //using ‘in’ object

      int length = original.length();            //finding length of the //inputted string

      for ( int i = length - 1 ; i >= 0 ; i-- )  //using for loop //getting each character by using charAt(i) method

         reverse = reverse + original.charAt(i);  //reversed string is //stored in reverse string

      System.out.println("Reverse of entered string is: "+reverse);

//reversed sting is outputted to user

   }

}

Java Interview questions

·        Collections in java

·        Interfaces in java

·        Why static is used in public static void main()

Question

·        Difference between jre and jdk

Answer

·        JRE: Java Runtime Environment.

JRE basically the Java Virtual Machine where Java programs run on and  also includes browser plugins for Applet execution.

·        JDK: Java Development Kit

It is a Software Development Kit for Java, including JRE, and compilers and tools (eg. JavaDoc,, Java Debugger) to create and compile programs.

Final Variable With Example

There is a final variable a, we are going to change the value of this variable, but It can't be changed because final variable once assigned a value can never be changed.

Example Program

class Super

{

                       final int a=100;

                       void show()

                       {

                        //a=200;error , can't be changed because final variable once assigned a value can never be changed.

                        System.out.println("Welcome to the final Keyword                       "+a);

                       }

}

class Demofinal

{

                       public static void main(String args[])

                       {

                        Super obj=new Super();

                        obj.show();

                       }

}

Output

D:\>javac Demofinal

D:\>java Demofinal

Welcome to the final Keyword    100