You can merge multiple presentations using the importContent() method of the XMLSlideShow class. Given below is the complete program to merge two presentations −

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

import org.apache.poi.xslf.usermodel.XMLSlideShow;
import org.apache.poi.xslf.usermodel.XSLFSlide;

public class MergingMultiplePresentations {
   
      public static void main(String args[]) throws IOException {
      
      //creating empty presentation
      XMLSlideShow ppt = new XMLSlideShow();
      
      //taking the two presentations that are to be merged 
      String file1 = "presentation1.pptx";
      String file2 = "presentation2.pptx";
      String[] inputs = {file1, file2};
      
      for(String arg : inputs){
      
         FileInputStream inputstream = new FileInputStream(arg);
         XMLSlideShow src = new XMLSlideShow(inputstream);
         
         for(XSLFSlide srcSlide : src.getSlides()) {
         
            //merging the contents
            ppt.createSlide().importContent(srcSlide);
         }
      }
     
      String file3 = "combinedpresentation.pptx";
      
      //creating the file object
      FileOutputStream out = new FileOutputStream(file3);
      
      // saving the changes to a file
      ppt.write(out);
      System.out.println("Merging done successfully");
      out.close();
   }
}

Save the above code as MergingMultiplePresentations.java, and then compile and execute it from the command prompt as follows −

$javac MergingMultiplePresentations.java
$java MergingMultiplePresentations

It will compile and execute to generate the following output −

Merging done successfully

The following snapshot shows the first presentation −

The following snapshot shows the second presentation −

Given below is the output of the program after merging the two slides. Here you can see the content of the earlier slides merged together.