Java Applet to display text in a colored oval

[Betty Christiansen]

I have written a program to enter a name in a text box of an html file, get the name in a Servlet, search for the name in the database and inform the user whether or not the name is in the database via an applet. I'm trying to get the information from the applet to display in a colored oval, green w/white font if the name is in the database and red w/black font if the name is not in the database. I can get the information to display just not in the colored ovals and text that I want, any assistance is appreciated. I am including only the applet code, not the HTML or Servlet.

import java.applet.*;
import java.awt.Color;
import java.awt.Graphics;
import java.sql.*;

public class MyApplet extends Applet {
	public void paint(Graphics page){
	  
    String name = null, message = null;
    //page.drawString("XXXXXXXXXXXXXXX", 20, 20);
    try {
	Class.forName("com.mysql.jdbc.Driver").newInstance();
	Connection con = DriverManager.getConnection(
        "jdbc:mysql://localhost:3306/databasea?user=root&password=root");
	Statement stmt = con.createStatement();
	stmt.executeQuery("use databaseA");
	ResultSet rs = stmt.executeQuery("Select * from tableB");
	while ( rs.next())
	  name = rs.getString(1);
	  
	  if(name.charAt(0) == '?')
	  page.setColor(Color.GREEN);
	  page.fillOval(10, 10, 180, 50);
	  page.setColor(Color.WHITE);
	  
	  message = name.substring(1) + " is in the table";
	  page.drawString(message, 30, 40);
	  
	  else
	  page.setColor(Color.RED);
	  page.fillOval(10, 10, 180, 50);
	  page.setColor(Color.BLACK); 
	  
	  message = name.substring(1) + " is not in the table";
	  page.drawString(message, 30, 40);
	  
	  String s = "delete  from tableB where name = \'" + name + "\'";
	  stmt.executeUpdate(s);
	  rs.close();
	  stmt.close();
	  con.close();
    } catch (Exception e) {
	System.out.println("Message: " + e);
	//System.exit(0);
    }
  }
}

[Campbell Ritchie]

Why are you still using Applets?

[Stephan van Hulst]

Hi Betty,

Why are you using applets at all? Applets are pretty much dead and buried, and come with lots of security issues. I would recommend using something different to display the outcome, such as JavaScript.

[Betty Christiansen]

Well this is for a class assignment, so there's that

[Paul Clapham]

I have to say that I'm not at all impressed by your course then. However it's not your fault that you are being taught in such a way, you just have to deal with it. So... could you tell us what you expected that code to do, and what it did instead? It would also help if we had some idea of what was in that database table.

[Betty Christiansen]

Thanks, I'm not impressed with this course either...enough said about that. So the idea behind this program is to enter a name in a text box of an html file, get the name in a Servlet, search for the name in the database and inform the user whether or not the name is in the database.

The database is MySQL and consists of two tables; tableA has three names entered into it via insert when the table was created, John Doe, Jane Doe, and David Paterson. TableB is used for the name being searched (entered in the text field of the HTML). If the name is found a question mark is inserted followed by the name. If it is not found an exclamation mark followed by the name. For example the name: David Doe is not in the above table therefore !David Doe is inserted in tableB. But for John Doe ?John Doe is inserted in tableB. The applet is using this table (tableB) to display a message telling the name is (or is not) in the table.

It's fairly convoluted. You enter a name in the HTML text field and click submit; that takes you to a servlet that displays the message/link "Click here to see the applet". When you click the link it displays another page that says, for example, "John Doe is in the table".

I have that all working correctly. Now the last step that I can't seem to get to work is to have that applet message "John Doe is in the table" display in a green oval w/white text, or if the name is not one of those three in the table the message should display in a red oval with black text. It just continues to display as regular text on a plain white background.

[Paul Clapham]

Your code doesn't use table A at all, it just looks at the single record in table B, decides it's in the table, and behaves accordingly. But there's this code:

      if(name.charAt(0) == '?')  
      page.setColor(Color.GREEN);  
      page.fillOval(10, 10, 180, 50);  
      page.setColor(Color.WHITE);  
        
      message = name.substring(1) + " is in the table";  
      page.drawString(message, 30, 40);  
        
      else  
      page.setColor(Color.RED);  
      page.fillOval(10, 10, 180, 50);  
      page.setColor(Color.BLACK);   
        
      message = name.substring(1) + " is not in the table";  
      page.drawString(message, 30, 40);  

I'm surprised that even compiles. Since you don't have any braces (the { and } characters), the scope of the "if" is only the line below it and nothing else. And so the "else" doesn't have any matching "if" before it and the compiler should complain about it. My guess is that you wanted to have braces like this:

      if(name.charAt(0) == '?')  {
        page.setColor(Color.GREEN);  
        page.fillOval(10, 10, 180, 50);  
        page.setColor(Color.WHITE);  
        
        message = name.substring(1) + " is in the table";  
        page.drawString(message, 30, 40);  
        
      }  else {  
        page.setColor(Color.RED);  
        page.fillOval(10, 10, 180, 50);  
        page.setColor(Color.BLACK);   
        
        message = name.substring(1) + " is not in the table";  
        page.drawString(message, 30, 40);  
      }

But even if you did that, the record you read from table B always has a ? at the beginning so you'll always see the "if" block being run and the "else" block never being run.

[Betty Christiansen]

Thank you for the help with the braces; I continually misplace those or omit them altogether, and you were right it wasn't compiling, I just couldn't figure out what I had left off. Regarding tableA it's actually part of the Servlet program, so all that works okay and the program recognizes either one of the three names in tableA or a new name and gives the correct response. However even with the braces in the correct spot I'm not getting the answer displayed as I want it. Thank you for the help, I guess I need to approach the professor (which is a whole other story)!

[Betty Christiansen]

Now I am told that is not how painting should be done EVER. Instead, I should have some method that can be called which builds a list of the results and then I should attempt to draw those results in the paint method. I should also be calling super.paint. I'm afraid as a beginner I'm not sure where to start with this advice. I already have the paint method, so do I need another method within that which creates a list of list of DB results? I'm only checking one name at a time so I'm not sure what that even means.

[Paul Clapham]

It's true, your posted code has numerous deficiencies. I preferred to get the basic problems sorted out before cleaning it up.

So, you're writing an applet. Have you learned about the applet's life cycle? If not, then have a look at the Oracle tutorial which explains it: Life Cycle of an Applet. That should help you extract some code which shouldn't be in your paint() method. Operations which only need to be done once... yes, you should put them in a different method than the paint() method, which is called repeatedly at times which you can't control. I'd suggest you fix that first.

[Betty Christiansen]

Thank you for that. I guess my understanding is flawed. I thought on an applet init was to set up the display, like background and foreground colors etc. and then if you wanted to draw on the applet you used paint. I apologize for the seemingly stupid questions but I wrote a little stand-alone applet to see if it would display the text the way I wanted and that worked, so I thought I could transfer that to my program. Apparently I thought wrong and just don't know where to place it now. This is the very first Java class I've taken and the only other programming or code writing I've done is HTML/CSS, so I'm way behind the curve here.

This is the code that worked for my stand-alone applet:

import javax.swing.JApplet;

import java.awt.*;

public class NewJApplet extends JApplet {	
	public void init(){
		setSize(400, 300);
	}
  public void paint(Graphics page){
	  page.setColor(Color.GREEN);
	  page.fillOval(10, 10, 180, 50);
	  page.setColor(Color.WHITE);
	  page.drawString("John Doe is in the table", 30, 40);
  }
}

[Paul Clapham]

Betty Christiansen wrote:I thought on an applet init was to set up the display, like background and foreground colors etc. and then if you wanted to draw on the applet you used paint.

Yes, that's exactly correct. Or not quite "exactly"... the init method is to set up everything that the applet is going to need, not just the displays. And yes, when you want to draw on the applet you use the paint method. But the paint method should only draw on the applet, nothing else.

They probably didn't tell you that the paint method will be called whenever the applet-viewer code decides that it needs to redraw the applet. So it's called the first time the applet is drawn. Then if you minimize the browser and then restore it, the paint method is called again. And if you maximize some other application in front of the browser and then minimize that application, the paint method is called again. That's why the paint method shouldn't be doing anything except drawing what you want drawn.

[Betty Christiansen]

Makes sense and no that detail hadn't been provided in class. Thank you for all the assistance.