Hello Guys
Below code will help you to build java applet in liferay portlet.

Write below code in view.jsp :

<applet name="Demo" id="Demo" code="com.AppletDemo" codebase='<%= themeDisplay.getCDNBaseURL()+"/PortletName" %>' width="450"  height="300">
    <param name="jnlp_href" value="AppletDemo.jnlp" />
     <param name="separate_jvm" value="true" />
</applet>

Create JNLP file for define jar file:

<?xml version="1.0" encoding="utf-8"?>
<jnlp spec="1.0+" codebase="" href="AppletDemo.jnlp">

<information>
    <title>AppletDemo</title>
    <vendor>Findnerd</vendor>
    <homepage href="http://www.Findnerd.com"/>
    <description>AppletDemo</description>
    <description kind="short">AppletDemo</description>
    <offline-allowed/>
</information>
<security>
    <all-permissions/>
</security>
<update check="timeout" policy="prompt-update"/>
    <resources>
        <j2se version="1.6+"/>
        <jar href="AppletDemo.jar" main="true"/>
        <jar href="Other-jar-files.jar"/>
    </resources>
    <applet-desc
        name="Demo"
        documentbase="view.jsp"
        main-class="com.AppletDemo.class"
        width="400"
        height="450">
    </applet-desc>
</jnlp>

Now write applet in AppletDemo.java

package com;

import javax.swing.JApplet;
import javax.swing.JLabel;
import java.awt.Font;

public class AppletDemo extends JApplet {

    /**
     * Create the applet.
     */
    public AppletDemo() {
        getContentPane().setLayout(null);

        JLabel lblNewLabel = new JLabel("Hello Bhagwan");
        lblNewLabel.setFont(new Font("SansSerif", Font.PLAIN, 18));
        lblNewLabel.setBounds(114, 78, 130, 51);
        getContentPane().add(lblNewLabel);

    }
}

Thank you.