GWT Interview Questions & Answers (2025)

GWT stands for Google Web Toolkit which is an open-source framework designed to build outer-performance web applications in Java. With GWT, you can write your front-end in Java and also can create high-performance AJAX applications in Java. As, for developers, it is very difficult to write web apps without any error, so GWT helps in making highly-optimized code by compiling the source code. It translates the Java code into JavaScript which in turn results in the JavaScript application.

Some useful parameters of GWT compiler:

• -out: the output files directory
• -gen: to write generated files in this directory
• -optimize: sets the optimization level of the compiler from 0 to 9
• -workdir: directory of compiler working
• -module: modules name to compile

Uses of GWT:

• It is a toolkit designed for building and optimizing browser-based applications.
• It has a built-in back button support which is a major benefit.
• To quickly build UI elements such as call trees, menu bars, etc., GWT has a dynamic and reusable UI components library.
• It has strong IDE support for error checking, auto-completion, easy code refactoring and many more.
• GWT produces JavaScript which is the most used in browsers as it is compatible and optimizable for every browser.

Requirements to install GWT:

• To install GWT, first install JDK Java Development Kit on your system as GWT is based on Java.
• JDK should be of version 1.6 or higher than this.
• No minimum requirement of memory, disk space, and operating system
• Install JRE and Eclipse
• Finally, install GWT SDK and plugins and then set up Apache.

It is one of the most important Java technologies with amazing features. Some cool features are:

• It provides excellent development tools like code refactoring, code navigation, etc. via eclipse.
• A single code base for client and server.
• It helps the server and client to quickly reloaded after making changes in it.
• In this, development tools are easy to install, for that, you need only two eclipse plugins.
• It supports IDE that helps with several coding tasks and errors.
• GWT generates a WAR file which makes easier for the deployment of applications.
• It provides a faster and reliable GUI layout.
• It also allows writing web applications offline, as it relies so little on the server.

CssResource allows you to insert CSS files into your application. Call CssResource.ensureInjected() at runtime to inject the content of the stylesheet.

ImageResource provides access to an image data in the most effective way.

TextResource allows you to access the content of a file which is contained in the compiled file.

Some standard modules are:

• User Module: It contains core GWT functionality
• HTTP Module: It consists of Low-level HTTP communications library
• JSON Module: It has JSON creation and parsing
• JUnit Module: It contains JUnit testing framework integration
• XML Module: It includes XML document creation and parsing

AsyncDataProvider ties your cell widgets to an asynchronous data source. The AsyncDataProvider used to fetch the new data when the cell widget requires new data and then push it to the widget. To request the new data, implement the oRangeChanged() method for the specified cell widget. To push the data, call updateRowCount() and/or updateRowData() methods.

UiBinder is a framework used to separate the functionality and view of a user interface. It allows developers to build GWT applications such as HTML pages with GWT widgets.

• It collaborates with UI designers who like to work in XML, HTML, and CSS than Java source code
• It increases productivity as it is easy to create UI from scratch.
• It encourages the separation of the programming logic i.e. Java code from UI.
• It prefers lightweight HTML elements over heavyweight widgets and panel, which directly increase the use of browser resources efficiently.
• Provides direct support for internationalization that works well with GWT.
• Provides thorough compile-time verification of cross-checking from XML to java source and vice-versa.

It is not correct to say that GWT is meant to develop applications that run on browsers. As we know GWT is based on Java and translate Java to JavaScript, and also includes IDE and Ui support which helps to make web apps. You can make some application wrappers that takes JavaScript applications native to androids or other operating systems of mobiles. This is how you can design mobile apps with the use of a glue layer present in between native wrapper and GWT for a JavaScript app.

Yeah, it is true that you can't make apps only with GWT, instead, you need other libraries. Thus, it is fully possible to make apps using GWT by combining it with other libraries

Layout panels are the most general layout mechanism, upon which other layouts are built. Layout panel contains other widgets which control the way widgets to be shown on User Interface. The panel widgets follow the properties of panel class which means inherits properties from panel class. These panel class takes the properties from widget class which in turns takes the properties from UIObject class.

List of Basic panels available in GWT:

• Root panel: it is the topmost panel and all other widgets are attached are attached to it. Use RootPanel.get(String id) to obtain a panel for any other element on the page.
• Flow panel: It is the simplest panel which creates a single
  element and attaches children to it without any modification.
• HTML panel: This panel offers a simple way to define HTML structures, most commonly used in UiBinder templates.
• Form panel: it is used to reproduce the behavior of an HTML form.
• Scroll panel: it is used to create a scrollable area within another panel.
• Popup panel and DialogBox panel: To create simple pops and dialogs, these panels are used.
• Grid and Flex table: these are used to create HTML table elements.