[SOLVED] Eclipse Plugin: Adding Custom Suggestion in Default Code Completion Pop-up window

I'm making an eclipse plugin that requires to add some custom suggestions in the default eclipse pop-up window. For doing so, I came to know from eclipse doc that I have to implement the IJavaCompletionProposalComputer to participate in content assist process . Accordingly, I tried the below implementation found in github. I understand that it overrides the computeCompletionProposals() method that computes suggestions and returns as ICompletionProposal List. But I failed to find what to do for adding my custom suggestions in the default pop-up window.

Any idea how I can do that?

package zzz.handlers;

import org.eclipse.core.commands.AbstractHandler;
import org.eclipse.core.commands.ExecutionEvent;
import org.eclipse.core.commands.ExecutionException;
import org.eclipse.ui.IWorkbenchWindow;
import org.eclipse.ui.handlers.HandlerUtil;
import org.eclipse.jface.dialogs.MessageDialog;
import org.eclipse.core.runtime.IProgressMonitor;
import org.eclipse.jface.text.contentassist.CompletionProposal;
import org.eclipse.jface.text.contentassist.ICompletionProposal;
import org.eclipse.jface.text.contentassist.IContextInformation;
import org.eclipse.ui.texteditor.HippieProposalProcessor;
import org.eclipse.jdt.ui.text.java.ContentAssistInvocationContext;
import org.eclipse.jdt.ui.text.java.IJavaCompletionProposalComputer;
import java.util.*;

/**
 * Our sample handler extends AbstractHandler, an IHandler base class.
 * @see org.eclipse.core.commands.IHandler
 * @see org.eclipse.core.commands.AbstractHandler
 */
/**
 * A computer wrapper for the hippie processor.
 *
 * @since 3.2
 */
public final class HippieProposalComputer implements IJavaCompletionProposalComputer {
    /** The wrapped processor. */
    private final HippieProposalProcessor fProcessor= new HippieProposalProcessor();

    /**
     * Default ctor to make it instantiatable via the extension mechanism.
     */
    public HippieProposalComputer() {
    }

    /*
     * @see org.eclipse.jface.text.contentassist.ICompletionProposalComputer#computeCompletionProposals(org.eclipse.jface.text.contentassist.TextContentAssistInvocationContext, org.eclipse.core.runtime.IProgressMonitor)
     */
    @Override
    public List<ICompletionProposal> computeCompletionProposals(ContentAssistInvocationContext context, IProgressMonitor monitor) {
        return Arrays.asList(fProcessor.computeCompletionProposals(context.getViewer(), context.getInvocationOffset()));
    }

    /*
     * @see org.eclipse.jface.text.contentassist.ICompletionProposalComputer#computeContextInformation(org.eclipse.jface.text.contentassist.TextContentAssistInvocationContext, org.eclipse.core.runtime.IProgressMonitor)
     */
    @Override
    public List<IContextInformation> computeContextInformation(ContentAssistInvocationContext context, IProgressMonitor monitor) {
        return Arrays.asList(fProcessor.computeContextInformation(context.getViewer(), context.getInvocationOffset()));
    }

    /*
     * @see org.eclipse.jface.text.contentassist.ICompletionProposalComputer#getErrorMessage()
     */
    @Override
    public String getErrorMessage() {
        return fProcessor.getErrorMessage();
    }

    /*
     * @see org.eclipse.jdt.ui.text.java.IJavaCompletionProposalComputer#sessionStarted()
     */
    @Override
    public void sessionStarted() {
    }

    /*
     * @see org.eclipse.jdt.ui.text.java.IJavaCompletionProposalComputer#sessionEnded()
     */
    @Override
    public void sessionEnded() {
    }
}

My plugin.xml is as follows...

<?xml version="1.0" encoding="UTF-8"?>
<?eclipse version="3.4"?>
<plugin>

 <extension point="org.eclipse.jdt.ui.javaCompletionProposalComputer"
       id="WordCompletionProposalComputer"
       name="Word Completion Proposal Computer">
       <javaCompletionProposalComputer
          class="org.eclipse.jdt.internal.ui.text.java.HippieProposalComputer"
          categoryId="org.eclipse.ui.texteditor.textual_proposals">
          <partition type="__java_javadoc"/>
       </javaCompletionProposalComputer>
     </extension>

   <extension
         point="org.eclipse.ui.commands">
      <category
            name="Sample Category"
            id="zadawdaw.commands.category">
      </category>
      <command
            name="Sample Command"
            categoryId="zadawdaw.commands.category"
            id="zadawdaw.commands.sampleCommand">
      </command>
   </extension>
   <extension
         point="org.eclipse.ui.handlers">
      <handler
            commandId="zadawdaw.commands.sampleCommand"
            class="zadawdaw.handlers.SampleHandler">
      </handler>
   </extension>

   <extension point="org.eclipse.jdt.ui.javaCompletionProposalComputer"
   id="textual_proposals"
   name="Text Proposals">
   <proposalCategory icon="icons/wordcompletions.png"/>
 </extension>

   <extension
         point="org.eclipse.ui.menus">
      <menuContribution
            locationURI="menu:org.eclipse.ui.main.menu?after=additions">
         <menu
               label="Sample Menu"
               mnemonic="M"
               id="zadawdaw.menus.sampleMenu">
            <command
                  commandId="zadawdaw.commands.sampleCommand"
                  mnemonic="S"
                  id="zadawdaw.menus.sampleCommand">
            </command>
         </menu>
      </menuContribution>
      <menuContribution
            locationURI="toolbar:org.eclipse.ui.main.toolbar?after=additions">
         <toolbar
               id="zadawdaw.toolbars.sampleToolbar">
            <command
                  commandId="zadawdaw.commands.sampleCommand"
                  icon="icons/sample.png"
                  tooltip="Say hello world"
                  id="zadawdaw.toolbars.sampleCommand">
            </command>
         </toolbar>
      </menuContribution>
   </extension>

</plugin>