Question

public Class GUi(){
 // More Code

public void onClick(ClickEvent event) {

LoginServer loginServer =new  LoginServer(getTextBoxUsername().getText(),getTextBoxPassword().getText());     
loginServer.setConnection(connection);
connection=loginServer.getConnection();
System.out.println(" connected "+connection);
// More code
}

public class LoginServer {
// more code
public void setConnection(Boolean connection) {

    String[] authentication = {username,password};
    //RPC call
    connectionService.connectionServer(authentication, callbackConnection); 
    System.out.println("setConnection" + connection);
}

public Boolean getConnection() {
    return connection;
}
AsyncCallback callbackConnection = new AsyncCallback() {

    public void onFailure(Throwable caught) {
        // TODO Auto-generated method stub
        connection=false;
    }

    public void onSuccess(Object result) {
        connection=true;
        System.out.println("onSuccess + connection);

    }
};

}

Output

setConnectionnull
connected null
onSuccesstrue

According to Me the Output should be.

 onSuccesstrue
 setConnectiontrue
 connected null

Because I made object of LoginServer ; Then I call method setConnection where there is RPC call written which is working perfectly fine.
OnSucces will change the value of connection.
Then I called method getConnection .

I also don’t understand why connected null

Answer 1

When/if you ask your wife/girlfriend to bring you a beer, you don’t have that beer in your hand the second after you asked her, and you can continue watching the match and reacting, you’re not blocked waiting for your beer: that’s called asynchronous processing.

Similarly, connection is still null the second after you send your RPC call.

See https://groups.google.com/d/msg/Google-Web-Toolkit/-soVdfMGug8/vRmqIcAZ5zsJ