Thank you so much for your input! The information you gave is great, although where you said: " You can of course synchronize all the actions which operate on the `accBalance` variable but that would effectively mean only a "single" client would be able to work with the `accBalance` variable thereby killing any chances of concurrent requests being processed"
I think this is exaclty what my college wants me to do, not very practical or very effective, but it's just to teach us how synchronization works etc etc. If I were to do this then, would I just make the doPost method synchronized and the rest will fall into place or should i make a synchronized(){....} section of code somewhere INSEIDE the doPost method?
Synchronize access to the instance variable, accBalance. Because accBalance is a double and not an object, it cannot be used as the monitor. Use synchronized methods or synchronized blocks of code, as appropriate. Simultaniously test two threads. Because the threads can complete too quickly to determine if they are interfering with each other, delay the adding of a deposit by inserting the following code within the synchronized block or method:
I've been strugling with this thing for weeks now, I just don't get Synchronization. I've tried reading up on it but it just doesn't help me. I'm not asking anybody to do this for me, I just want some advice, a push in the right direction etc.. This is the code that I have to Synchronize:
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.text.DecimalFormat;
public class SyncBank extends HttpServlet
{
// Create Class Variable
DecimalFormat myFormat = new DecimalFormat("$#,000.00");
double accBalance = 0.00;
public void doGet(HttpServletRequest req,HttpServletResponse res)
throws ServletException, IOException
{
doPost(req,res);
}
public void doPost(HttpServletRequest req,HttpServletResponse res)
throws ServletException, IOException
{
//Set MIME type of content returned to browser
res.setContentType("text/html");
PrintWriter out = res.getWriter();
//Starts outputting the HTML Form
out.println("<html><head>" +
"<title>Online Bank Simulator</title>" +
"</head><body>" +
"<hr color=\"#808000\">" +
"<center><h1>Banking Simulation</h1></center>" +
"<form method=\"POST\" action=\"../servlet/HTMLBank\">" +
"<center>Amount: <input type=\"text\" name=\"Amount\" size=\"20\"></center>");
//Decides which action to take
String action = req.getParameter("act");
if(action != null)
{
if(action.equals("Deposit"))
{
double amount;
String strAmount …
I got this assignment where I need to set a session attribute. Although I'm having problems since I cant set attribute that is of type double? I got these hints but since I've worked with doubleValue() or downcasting, the hints didn't help me much..
Hints: -Recall that session attributes are stored as objects and must be downcast. -Because a Double object cannot be modified, use the Double method, doubleValue(),to return an intrinsic double value.
My code:
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.text.DecimalFormat;
public class SessionBank extends HttpServlet
{
// Create Class Variable
DecimalFormat myFormat = new DecimalFormat("$#,000.00");
public void doGet(HttpServletRequest req,HttpServletResponse res)
throws ServletException, IOException
{
doPost(req,res);
}
public void doPost(HttpServletRequest req,HttpServletResponse res)
throws ServletException, IOException
{
//Makes instance variable a local variable
double accBalance = 0.00;
//Set MIME type of content returned to browser
res.setContentType("text/html");
PrintWriter out = res.getWriter();
//Starts outputting the HTML Form
out.println("<html><head>" +
"<title>Online Bank Simulator</title>" +
"</head><body>" +
"<hr color=\"#808000\">" +
"<center><h1>Banking Simulation</h1></center>" +
"<form method=\"POST\" action=\"../servlet/HTMLBank\">" +
"<center>Amount: <input type=\"text\" name=\"Amount\" size=\"20\"></center>");
//Decides which action to take
String action = req.getParameter("act");
if(action != null)
{
if(action.equals("Deposit"))
{
double amount;
String strAmount = req.getParameter("Amount");
amount = Double.parseDouble(strAmount);
if(amount <= 0.00)
{
out.println("<h2>Error: The amount is either null or a minus</h2>");
}
else
{
accBalance = accBalance + amount;
out.println("<br><center>Balance:"+myFormat.format(accBalance)+" </center> <br>");
}
}
else if(action.equals("Withdraw"))
{
double amount;
String strAmount = req.getParameter("Amount");
amount = Double.parseDouble(strAmount);
if(amount <= 0.00)
{
out.println("<h2>Error: The amount is either null …
Well at the moment it's a instance variable.. Will give the it a try as a class variable tonight, hope it works.
It does make sense though doesn't it? Instance variables have separate values for each instance of a class. Class variables maintain a single shared value for all instances of the class.
Will let you know if it works, Thanks for the tip!
I'm struggling with a servlet that's suppose to represent an "online banking service". Once you run the servlet you'll see it's an extremely simple example... You enter an amount in the textfield provided, then click on the apropriate button depeding what action you want to perform e.g. "deposit","withdraw" and "balance". Your balance then is displayed in a label underneath the textfield.
Now the problem is: I had to assign a default value for accBalance (0.00). Now everytime I deposit money in, for example $50, my balance does show $50. But when I want to do another diposit ontop of that, e.g. another $100. You'd think that the balance now should be $150 right? ..It doesn't, it then displays $100.. The reason for this (I think) is that everytime the servlet is re-loaded the accBalance is again set to 0.00.
*Once you run the servlet and test it out you'll see what I mean*
The code:
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
public class HTMLBank extends HttpServlet
{
public void doGet(HttpServletRequest req,HttpServletResponse res)
throws ServletException, IOException
{
doPost(req,res);
}
public void doPost(HttpServletRequest req,HttpServletResponse res)
throws ServletException, IOException
{
//Create variable
double accBalance = 0.00;
//Set MIME type of content returned to browser
res.setContentType("text/html");
PrintWriter out = res.getWriter();
try{
//Starts outputting the HTML Form
out.println("<html><head>" +
"<title>Online Bank Simulator</title>" +
"</head><body>" +
"<hr color=\"#808000\">" +
"<center><h1>Banking Simulation</h1></center>" +
"<form method=\"POST\" action=\"../servlet/HTMLBank\">" +
"<center>Amount: <input type=\"text\" name=\"Amount\" size=\"20\"></center>");
// Gets input from user
//String strAmount = req.getParameter("Amount");
//Decides which …
Does anybody know what this "WSaction" is? What it does and most importantly how it works?
I've tried googling this but hardly found ANYTHING.. I'm busy working with Servlets and as far as I can tell it checks what button was pressed in the HTML form..
But I'm not too sure, any help would greatly be appreciated!
Name's Dean, I'm a java student here in sunny South Africa.. Very impressed by daniweb! Been with other IT communities, and daniweb seems way more ontop of things. Other than that, I'm excited on helping other java students like myself. And I still have tons of questions that need answering also...
Okay so the difference between Swing and an Applet..
Applets are little programs imbedded in websites/HTML pages. Applets also are more commonly used for small single tasks in webpages.
Swing programs however, would probably be the better choice in your situation. Swing acctualy refers to a class in the java language that defines/handles GUI(Graphical user interface) components like(like buttons, labels, textfields etc).
So just depends what program you want. Do you want a standalone java program (swing) or do you want a java program imbedded in a website(applet).
