Top GWT (Google Web Toolkit) Interview Questions and Answers

What is GWT?

GWT (Google Web Toolkit) is an open-source Java software development framework that makes it easier to build and maintain complex browser-based applications. It allows developers to use Java to create client-side code that's then compiled into highly optimized JavaScript. GWT handles many browser-specific complexities, streamlining the development process.

GWT Operation Modes

  • Development Mode: Runs the application in a Java Virtual Machine (JVM) environment, enabling Java debugging capabilities. This is useful for testing and development.
  • Web Mode: Compiles the Java code to JavaScript; the application is deployed to a web server and runs in the user's browser.

Components of GWT

  • Java-to-JavaScript Compiler: Translates Java code to JavaScript.
  • Development Mode: Provides tools for debugging Java code.
  • JRE Emulation Library: Provides a subset of the Java Runtime Environment (JRE) API for use in GWT applications.
  • Web UI Class Library: Provides a set of widgets and UI components.

GWT Module Descriptor

A module descriptor (*.gwt.xml) configures your GWT application. It specifies the entry point and other settings.

GWT Modules

GWT modules group related classes and interfaces, providing a mechanism for organizing code into logical units.

Enabling Assertions in GWT

Use the -ea (enable assertions) flag when compiling your GWT application with the GWT compiler. Assertions help in debugging but are generally removed in production builds.

Default GWT Widget Styles

GWT widgets have default CSS class names that start with gwt- (e.g., gwt-Button, gwt-TextBox).

Internationalization in GWT

Internationalization (i18n) is the process of adapting your application to support multiple languages and locales. GWT provides mechanisms for managing localized resources.

Host Page in GWT

The host page is an HTML file that includes your GWT application. It provides the initial HTML context for your GWT application to run within a browser.

RPC (Remote Procedure Call) in GWT

GWT RPC is a mechanism for making remote procedure calls from your GWT client-side code to a server-side service. It simplifies communication with server-side logic.

GWT ClientBundle

The ClientBundle interface helps manage static resources (CSS, images, etc.) that are bundled with your GWT application. This improves the efficiency of loading these resources into your application.

GWT Panels

GWT provides various panel widgets for structuring and organizing UI elements.

  • RootPanel: The top-level panel.
  • FlowPanel: Simple HTML flow layout.
  • HTMLPanel: Embeds HTML content.
  • FormPanel: Wraps widgets in an HTML form.
  • ScrollPanel: Adds scrollability.
  • Grid: Creates HTML tables.
  • FlexTable: A more flexible table layout.

Layout Panels in GWT

Layout panels manage the layout of widgets within a user interface. They inherit from the Panel class.

GWT JSON

GWT supports JSON (JavaScript Object Notation), a lightweight data-interchange format commonly used for communication between web applications and servers.

Parsing XML in GWT

GWT provides XML parsing capabilities using the XMLParser class. The parser converts XML text into a DOM (Document Object Model) tree for easy manipulation.

Nodes Created by GWT XML Parsing

  • Element: Represents XML elements.
  • Text: Represents text content.
  • Comment: Represents XML comments.
  • Attr: Represents element attributes.

GWT Database Dependencies

GWT supports various database technologies. Dependencies (like database drivers) need to be included in your project.

GWT History Mechanism

GWT's history mechanism uses URL fragment identifiers (#) to track application state in the browser's history. This creates bookmarkable and shareable URLs, mimicking the behavior of standard web navigation.

GWT History Tokens

History tokens are strings representing different states in your GWT application, tracked in the browser's URL.

Creating Custom Widgets in GWT

You can create custom widgets in GWT by combining existing widgets and adding custom behavior. This involves using Java and optionally the JavaScript Native Interface (JSNI).

JSNI (JavaScript Native Interface)

JSNI is a mechanism for integrating existing JavaScript code or libraries with GWT applications. This allows accessing lower-level browser features or interfacing with third-party JavaScript code.

Uses of JSNI

  • Calling JavaScript from Java.
  • Calling Java from JavaScript.
  • Implementing methods directly in JavaScript.
  • Handling exceptions.
  • Accessing browser features not exposed through GWT's API.