Java/GWT/RootPanel

Add two controls to RootPanel

package com.jexp.gwt.client;

import com.google.gwt.core.client.*;
import com.google.gwt.user.client.ui.*;
public class GWTClient implements EntryPoint{
   public void onModuleLoad() {
      final Button button = new Button("Click me");
      final Label label = new Label();
      
      button.addClickListener(new ClickListener() {
         public void onClick(Widget sender) {
            if (label.getText().equals(""))
               label.setText("Hello World!");
            else
               label.setText("");
         }
      });
      
      RootPanel.get("slot1").add(button);
      RootPanel.get("slot2").add(label);
      
   }
   
}

Use RootPanel to Load New Page

package com.jexp.gwt.client;
import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.core.client.GWT;
import com.google.gwt.user.client.Window;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.user.client.ui.ClickListener;
import com.google.gwt.user.client.ui.Grid;
import com.google.gwt.user.client.ui.Label;
import com.google.gwt.user.client.ui.PasswordTextBox;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.user.client.ui.TextBox;
import com.google.gwt.user.client.ui.Widget;
public class GWTClient implements EntryPoint{
  public void onModuleLoad() {
    loadLoginView();
  }
  private void loadLoginView() {
    final Label loginPrompt = new Label("login");
    final Grid grid = new Grid(3, 2);
    final Label namePrompt = new Label("name");
    final TextBox nameTextbox = new TextBox();
    final Label passwordPrompt = new Label("password");
    final PasswordTextBox passwordTextbox = new PasswordTextBox();
    final Button button = new Button("Login");
    button.addClickListener(new ClickListener() {
      public void onClick(Widget sender) {
        loadWelcomeView();
      }
    });
    button.addClickListener(new ClickListener() {
      public void onClick(Widget sender) {
        Window.alert("New page loaded");
      }
    });
    loginPrompt.addStyleName("loginPrompt");
    nameTextbox.addStyleName("nameField");
    passwordTextbox.addStyleName("passwordField");
    grid.setWidget(0, 0, namePrompt);
    grid.setWidget(0, 1, nameTextbox);
    grid.setWidget(1, 0, passwordPrompt);
    grid.setWidget(1, 1, passwordTextbox);
    grid.setWidget(2, 1, button);
    
    RootPanel.get().clear();
    RootPanel.get().add(loginPrompt);
    RootPanel.get().add(grid);
  }
  private void loadWelcomeView() {
    final Label welcomeMsg = new Label("welcome");
    welcomeMsg.addStyleName("welcomeMsg");
    RootPanel.get().clear();
    RootPanel.get().add(welcomeMsg);
  }
}