How to Run Applet Program in Java

Applet in Java

In order to understand how to run applet program in Java we first need to know about applets in Java.

Java applets are compact, cross-platform Java programs that may be easily integrated into web pages. They can be executed as interactive elements within web documents or desktop applications, hosted on internet servers, and easily shared online. Applets can be seen using programs like the Applet Viewer and have their own life cycle processes. To ensure a secure execution environment, they do, however, come with constraints, such as those on file operations, network connections, and the capacity to launch external programs on the host.

Hierarchy of Applet

As shown, the Applet class is a derived class of the Panel class, which, in its own right, derives from the Container class, and the Container class is, in turn, a subclass of Component.

Let's understand the significance of each class:

1. Object: As you can see it's on the top of hierarchy since All Java classes implicitly inherit from this class Methods defined by the object class includes: equals(), hashCode(), toString(), and getClass(), these are also inherited by all other classes in Java.
2. Component: The Component class is a core element for graphical user interface components, such as buttons, labels, and text fields. It provides methods for rendering, user input, and essential GUI functionality shared by all components.
3. Container: Containers are components that can hold other components.They are a subclass of component class. They are used for creating complex user interfaces by organizing and arranging other components within them. Common subclasses of Container includes: Panel, Window, and Frame.
4. Panel: The Panel class is a lightweight container that can be used to group and organize components within a user interface. It is often used to group related components together. Panels can be added to other containers like Frame or Applet to create more complex layouts.
5. Applet: The Applet class is a Java program meant for embedding interactive content within web pages. It includes GUI components as it extends the Panel class. While once popular in web apps, they are less common now due to HTML5 and JavaScript.
6. JApplet: This class extends the Applet class with Swing, a versatile GUI toolkit in Java. JApplet enhances applets with richer user interfaces using Swing components, enabling more advanced graphical capabilities compared to standard applets.

Lifecycle Methods for Applet:

The java.applet.Applet class presents four distinct life cycle methods, whereas the java.awt.Component class furnishes a solitary life cycle method for applets.

To learn more about Java applets, you can explore one of our articles: Applet life cycle in java

Applet within a Java Compatible Web Browser

Suppose we have a STApplet.java file in which we have our java code

• Compiling: javac STApplet.java
• Create an Html file and embed the Applet tag in the HTML file.

In order to execute an applet within a web browser, it is necessary to generate an HTML text file containing a tag responsible for loading the applet. To accomplish this, we can employ either the APPLET or OBJECT tags.

a. Attributes in applet tag:

• Code: This attribute designates the applet class name to be loaded in the web browser.
• Width: It defines the applet's width.
• Height: This attribute establishes the applet's height.

Let's see an example of an HTML file that initiates the HelloWorld applet using the APPLET tag:

Let's see the STApplet.html file

b. Output

The applet STApplet.class is loaded into the browser when you access STApplet.html.

Note: In order to load an applet program, the browser must have java enabled.

How to Use Applet Viewer to Run Applet?

The Applet Viewer is a Java application designed for applet visualization, serving as a miniature browser-like tool for assessing an applet's potential appearance within a browser. It operates by identifying the APPLET tag, which must be included in the source code file within comment sections.

Here are the steps to utilize the Applet Viewer:

1. Embed the HTML APPLET tag within comment blocks in the source file.
2. Compile the applet source code using the javac compiler.
3. Utilize the Applet Viewer by running the command appletviewer ClassName.class to preview the applet.

To use the applet viewer tool for executing the applet, input the following command in the command prompt:

Security Considerations

As security is often considered a significant concern when working with Java applets, especially in the context of web applications.

Here are some key security considerations and best practices for Java applets:

1. Signed Applets:
   • Secure Java applets by signing with trusted digital certificates (CA).
2. Sandboxing:
   • Java applets run in a restricted sandboxed environment for security.
3. Security Permissions:
   • Use permissions to avoid excessive access requests and enhance security.
4. User Consent:
   • Inform users about the necessity of specific applet permissions.
5. Regular Updates:
   • Ensure applets stay current with security patches and Java updates.
6. Monitoring and Incident Response:
   • Establish monitoring and incident response procedures for swift security incident handling.

Advantages of Applet

• Applets typically have the capability to establish network connections with their originating host.
• Applets running within a web browser can seamlessly trigger the display of HTML documents.
• Applets can call public methods of other applets located on the same page.
• Applets loaded from the local file system (from a directory within the user's CLASSPATH) are free from the restrictions that apply to applets loaded from remote sources.
• While most applets halt when you navigate away from their page, they have the flexibility to continue running if required.
• Applets are well-suited for performing various small tasks like login procedures, inventory checks, and task scheduling over Intranets.
• In comparison to stand-alone applications, applets are compact in size, making them advantageous for efficient network transfer.

Limitations of Using Applet

1. Given that the applet must operate within a web browser, the advantage of utilizing an exceptionally fast physical/logical middle-tier machine in a 3-tier environment is not available. Instead, the processing speed relies on the resources of individual web browsers, as well as the speed and bandwidth of the network.
2. Current browsers impose several restrictions on applets loaded from the network, including:
   • Applets cannot load libraries or define native methods.
   • They typically cannot read or write files on the host where they are executed.
   • They are generally limited in making network connections, often restricted to the host from which they originated.
   • Applets are unable to initiate any programs on the host where they are executed.
   • Certain system properties may be inaccessible.
   • Windows created by an applet may have a different appearance compared to those generated by an application.
3. The utilization of a proxy server for web access can lead to automatic failures in Java installation and updates. Consequently, specific Java requirements may not be met unless Java is manually installed or updated.