Java inserting value to MySQL and returning values from MySQL

Question

I'm creating a employee login validation class where i can insert their to mysql database their information then for validation i'm trying to select only the password of the row. here's my code:

     import java.sql.*;
        import java.sql.PreparedStatement;
        import java.sql.Connection;


    public class Employee 
    {

    private PreparedStatement statement;
    private Connection con;
    private String pass;
    public Employee()
    {   

    }
    public Employee(String firstName, String lastName, String userID, String userPassword, String role )
    {
        try
        {
            Class.forName("com.mysql.jdbc.Driver");
            con = DriverManager.getConnection("jdbc:mysql://localhost:3306/test","root","");
            statement = con.prepareStatement("Insert into employee(firstName, lastName, userID, " +
                    "password, role)values(?, ?, ?, ?, ?)");    

            statement.setString(1, firstName);
            statement.setString(2, lastName);
            statement.setString(3, userID);
            statement.setString(4, userPassword);
            statement.setString(5, role);
            statement.executeUpdate();
            con.close(); 
        }
        catch(Exception e)
        {

        }
    }
    public void setPassword(String userID)
    {
        try
        {
            statement = con.prepareStatement("SELECT * from employee WHERE userID = ?");
            statement.setString(1, userID);
            ResultSet rs = statement.executeQuery();
            while(rs.next()){
                pass = rs.getString(4);
            }
        }
        catch(Exception e)
        {
            System.out.print(e);
        }
    }
    public String getPassword()
    {
        return pass;
    }


    }
and here is my main

        public class TestMain 
        {
        public static void main(String argsp[])
    {
        Employee emp = new Employee();
        emp.setPassword("ecka12");  
    }
    }

i got a null pointer exception i don't know why.

Rohit Jain · Accepted Answer · 2012-10-05 13:18:27Z

You are creating object using: -

   Employee emp = new Employee();

In your 0-arg constructor you have not initialized your connection

public Employee() {

}

So, when you use con in setPassword() method, you will get NullPointerException : -

    // con is not initialized
    statement = con.prepareStatement("SELECT * from employee WHERE userID = ?");
    statement.setString(1, userID);

To correct this, you need to move the below code to 0-arg constructor.. And in your other constructor: - add this() as your first statement..

public Employee() {
    try {
         Class.forName("com.mysql.jdbc.Driver");
         con = DriverManager.getConnection(
                        "jdbc:mysql://localhost:3306/test","root","");
    } catch (Exception e) {
         e.printStackTrace();
    }
}



public Employee(String firstName, String lastName) {
     this(); // Initialize con..

     try {
        // You don't need to initialize your con here again..
        // Your remaining code.. 
     }
}

PbxMan · Accepted Answer · 2012-10-05 12:59:04Z

0

the null pointer exception happens because you have an extra constructor public Employee() , con is not initializing therefore is causing a null pointer exception.

Good Luck!

answered Oct 5, 2012 at 12:59

PbxMan

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Comments

thar45 · Accepted Answer · 2012-10-05 13:28:46Z

0

1.Make sure the employee table is created before you are executing your code , because you have n't created the table in java code .

2.Employee(String,,,,) constructor have not used also ,because of this Connection did not get instantiated, you have closed the connection in constructor itself . so it may exist before searching for data in your table.

edited Oct 5, 2012 at 13:28

answered Oct 5, 2012 at 13:23

thar45

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