Designing table for client/server situation ....

I am designing table that will be accessed by concurrent users. It's structure is given below:
AccountID number(30) Primary Key
AccountName text(50)
I have a sequence named: "seqAccID" which increments AccountID and stores new ID.
I want to know what changes must be done in the table so that if concurrent users are creating entering in the same table and press enter at the same time there is no possibility of error: "Primary Key violation".

I have a sequence named: "seqAccID" which increments
AccountID and stores new ID.
I want to know what changes must be done in the table
so that if concurrent users are creating entering in
the same table and press enter at the same time there
is no possibility of error: "Primary Key violation".You don't need anything, sequences guarantee the uniqueness (that's their purpose). See http://download-uk.oracle.com/docs/cd/B19306_01/server.102/b14220/schema.htm#sthref883
If you use your own counter instead, then the For Update suggestion is correct.

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    import java.io.*;
    import java.net.*;
    import java.awt.*;
    import java.awt.event.*;
    import java.applet.*;
    import java.util.zip.*;
    public class Client extends Applet implements ActionListener {
    private TextField enter;
    private TextArea display;
    DataOutputStream output;
    DataInputStream input;
    private Button button, button2;
    URLConnection connection;
    private byte[] bytes1, bytes2;
    private String message, message2;
    public void init()
    setLayout( new BorderLayout() );
    enter = new TextField( " Enter text here " );
    enter.setEnabled( false );
    enter.addActionListener( this );
    add( enter, BorderLayout.NORTH );
    display = new TextArea( 4, 30 );
         display.setEditable( false );
    add( display, BorderLayout.CENTER );
         button = new Button( "Connect" );
         button.addActionListener( this );
         add( button, BorderLayout.SOUTH );
    public void runClient()
    Socket client;
    try {
    // Step 1: Create a Socket to make connection.
    display.setText( "Attempting connection\n" );
              URL currentpage = getCodeBase();
              String protocol = currentpage.getProtocol();
              String host = currentpage.getHost();
              int port = 8100;
              String urlsuffix = "/servlet/SocketServlet";
              URL dataurl = new URL( "http://localhost:8100/servlet/SocketServlet" );
              connection = dataurl.openConnection();
    connection.setDoOutput(true);
    connection.setDoInput(true);
    connection.setRequestProperty("Content-type", "application/octet-stream");
              connection.setUseCaches( false );
              display.append( "\nConnected to: " + host );          
    // Step 2: Get the output streams.
    output = new DataOutputStream(
    connection.getOutputStream() );
              display.append( "\n got output stream\n" );
              // Step 3 get input connection
              try
              display.append( "\nAttempting to connect to input stream\n" );
                   input = new DataInputStream( connection.getInputStream() );
                   bytes1 = new byte[1024];
                   input.readFully( bytes1 );
                   display.append( "\nGot input stream\n" );
                   message = new String( bytes1 );
                   display.append( "\n" + message + "\n" );          
              catch ( IOException ioex )
              // Step 3: Process connection.
              enter.setEnabled( true );
              do {
              try {
    bytes2 = new byte[1024];
              input.readFully( bytes2 );
              message2 = new String( bytes2 );
              display.append( "\n" + message2 );
              display.setCaretPosition(
              display.getText().length() );
              catch ( IOException ioex ) {
              display.append(
              "\nUnknown object type received" );
              } while ( !message.equals( "SERVER>>> TERMINATE" ) );
    // Step 4: Close connection.
    display.append( "Closing connection.\n" );
    output.close();
    input.close();
         catch (MalformedURLException mfe )
    catch ( EOFException eof ) {
    System.out.println( "Server terminated connection" );
    catch ( IOException e ) {
    e.printStackTrace();
    private void sendData( String s )
    try {
    message = s;
    output.writeBytes( "CLIENT>>> " + s );
    display.append( "\nCLIENT>>>" + s );
    catch ( IOException cnfex ) {
    display.append(
    "\nError writing object" );
    public void actionPerformed( ActionEvent e )
         if ( e.getActionCommand() == "Connect" )
              runClient();
         else
              sendData( e.getActionCommand() );
    public static void main(String args[])
    Frame f = new Frame("Chat Client");
         Client c = new Client();
         c.init();
         f.add("Center", c);
         f.setSize(300, 150);
         f.show();
    the connection appears to fail at client step 3, any help is super, thanks
    Aidan

    Hi,
    In your client you are trying to open OutputStream even though you are not using it.
    So there are two solutions here.
    1. If you dont need OutputStream your code shoud look like this
    try {
    // Step 1: Create a Socket to make connection.
    display.setText( "Attempting connection\n" );
    URL currentpage = getCodeBase();
    String protocol = currentpage.getProtocol();
    String host = currentpage.getHost();
    int port = 8100;
    String urlsuffix = "/servlet/SocketServlet";
    URL dataurl = new URL( "http://localhost:8100/servlet/SocketServlet" );
    connection = dataurl.openConnection();
    //connection.setDoOutput(true);
    connection.setDoInput(true);
    connection.setRequestProperty("Content-type", "application/octet-stream");
    connection.setUseCaches( false );
    display.append( "\nConnected to: " + host );
    // Step 2: Get the output streams.
    //output = new DataOutputStream(
    //connection.getOutputStream() );
    //display.append( "\n got output stream\n" );
    display.append( "\n Not interested in output stream\n" );
    //Step 3 Inpustream related
    // Step 4: Close connection.
    display.append( "Closing connection.\n" );
    //output.close();
    input.close();
    1. If you need OutputStream, close your OutputStream before even trying to get InputStream, your code should like this
    try {
    // Step 1: Create a Socket to make connection.
    display.setText( "Attempting connection\n" );
    URL currentpage = getCodeBase();
    String protocol = currentpage.getProtocol();
    String host = currentpage.getHost();
    int port = 8100;
    String urlsuffix = "/servlet/SocketServlet";
    URL dataurl = new URL( "http://localhost:8100/servlet/SocketServlet" );
    connection = dataurl.openConnection();
    //connection.setDoOutput(true);
    connection.setDoInput(true);
    connection.setRequestProperty("Content-type", "application/octet-stream");
    connection.setUseCaches( false );
    display.append( "\nConnected to: " + host );
    // Step 2: Get the output streams.
    output = new DataOutputStream(
    connection.getOutputStream() );
    display.append( "\n got output stream\n" );
    //I'll do whateve I've to do with outputstream
    //done with output stream closing
    output.close();
    //Step 3 Inpustream related
    // Step 4: Close connection.
    display.append( "Closing connection.\n" );
    //output.close();
    input.close();
    hope this works
    all the best,
    Raj

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