Coffee break #209. 4 Ways to Find Duplicates in Java List. How to Create a Simple Media Player Using Java

4 Ways to Find Duplicates in Java List

Source: Codippa This article covers various ways to find duplicates in a List. We call duplicates elements that appear more than once.

1. Using Set

Below is an algorithm to find duplicate elements in a Java List using Set .

• We create a new Java Set object and a new ArrayList to store duplicate elements.
• We perform an iteration or loop through the list.
• We add each element in the list to the Set using the add() method .
• As a result, add() returns true if the element was added, and false if the element was already present in the Set .
• If the element is already in the Set , it is a duplicate. Then we add it to the ArrayList .
• At the end of the iteration, the new ArrayList will contain all the duplicate elements from the original List ( List ).

An example program based on this algorithm is shown below.

List<Integer> numbers = List.of(1, 2, 3, 4, 3, 1, 2);
Set<Integer> set = new HashSet<>();
List<Object> duplicates = new ArrayList<>();
numbers.forEach(n -> {
  if (!set.add(n)) {
    duplicates.add(n);
  }
});
System.out.println("Duplicate elements: " + duplicates);

Conclusion: Note that we used the forEach() method to iterate through the List , but you can use any other method.

2. Using Map

Below are the algorithm steps for this method of finding duplicates in a List .

• Create a new Map object and a new ArrayList to hold duplicate elements.
• The keys of this Map will be the elements of the original List , and its values ​​will be the number of their occurrences in the List .
• Loop through the list ( List ).
• For each element in the List , check whether it exists as a key in the Map using the containsKey() method .
• If it exists, increment its value in the Map and add it again using the put() method .
• If it doesn't exist, add it to the Map with a value of 1.
• Once the list iteration is complete, all Map elements with a value greater than 1 become duplicates.
• Finally, iterate the Map and add those elements whose value is greater than 1 to a list to store duplicate elements.

An example program is shown below:

List<Integer> numbers = List.of(1, 2, 3, 4, 3, 1, 2);
Map<Integer, Integer> countMap = new HashMap<>();
List<Object> duplicates = new ArrayList<>();
numbers.forEach(n -> {
  if (countMap.containsKey(n)) {
    countMap.put(n, countMap.get(n) + 1);
  } else {
    countMap.put(n, 1);
  }
});
countMap.keySet().forEach(k -> {
  if(countMap.get(k)> 1) {
    duplicates.add(k);
  }
});

3. Using nested loops

If you are asked to find duplicate elements in a list without using any Collection classes like Set , Map and so on, then this method will be useful. Algorithm stages:

• Loop through the list ( List ).
• After the loop has been completed the first time, go back to the beginning and repeat the steps again to find each item in the rest of the list.
• If the current loop element is equal to any of the remaining elements, it is a duplicate.

A program written using this algorithm looks like this:

List<Integer> numbers = List.of(1, 2, 3, 4, 3, 1, 2);
List<Object> duplicates = new ArrayList<>();
for (int i = 0; i < numbers.size() - 1; i++) {
  for (int j = i + 1; j < numbers.size(); j++) {
    if (numbers.get(i).equals(numbers.get(j))) {
      duplicates.add(numbers.get(i));
    }
  }
}

4. Using Java Stream

This method is based on Java 8 threads and works like this:

• Convert List to Stream .
• Convert the stream to a Map using the collect() method . For example, key is each element in the list, and value is the number of occurrences.
• The collect() method returns and Map takes Collector as an argument. The Collector implementation determines the keys and values ​​of the resulting Map .
• Since we want the Map's keys to be the elements of a List and its values ​​to be the number of their occurrences, we can use Collectors.groupingBy() to create a collector .
• Once the Map has been created using groupingBy() , use the entrySet() method to obtain a set of Map.Entry objects .
• Filter records based on a value (that is, number of occurrences) greater than 1.
• Match the filtered records with their keys.

Example program:

List<Integer> numbers = List.of(1, 2, 3, 4, 3, 1, 2);
Map<Object, Long> map = numbers.
                        stream().
                        collect(
                          Collectors.
                          groupingBy(n -> n, Collectors.counting())
                        );
List<Object> duplicates = map.
                          entrySet().
                          stream().
                          filter(e -> e.getValue() > 1).
                          map(e -> e.getKey()).
        collect(Collectors.toList());

The groupingBy() method is used to group items in a collection based on certain criteria. Here is an example of how this method works:

• The criterion is provided as a lambda expression because groupingBy() takes a Function argument , which is a function interface.
• In this case, we group by identity function n -> n , which means we group the list elements by their values.
• The second argument to groupingBy() is another collector that specifies how the elements in each group should be combined.
• Here we use Collectors.counting() which creates a Map containing the count of each element in the list.

As a result, the resulting Map will contain a count of how many times each element appears in the list. We then filter the Map using the filter() method to find elements whose count is greater than 1, indicating that they are duplicates.

How to Create a Simple Media Player Using Java

Source: Medium This tutorial will help you create a simple media player in Java to play audio and video files. Developing a media player can be a great way to learn how to use Java's built-in libraries to work with media files. To accomplish this task, we will use JavaFX and the Graphical User Interface (GUI) toolkit for Java.

Step 1: Project Setup

First, we need to set up our Java project. We'll be using Eclipse as the IDE, but you can use any IDE of your choice. Create a new Java project and name it “MediaPlayer”. We will also need to add the JavaFX library to our project. To do this, go to the project properties and add the JavaFX library to the project's build path.

Step 2: Create the User Interface

Next we will create the user interface for our media player. It will be a simple user interface with a play button, a stop button and a media player panel that displays the video or audio file that we want to play. For our interface we will use the BorderPane layout . The media player panel will be in the center of the BorderPane, and the play and stop buttons will be at the bottom of the BorderPane. Here is the UI code:

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.BorderPane;
import javafx.scene.media.Media;
import javafx.scene.media.MediaPlayer;
import javafx.scene.media.MediaView;
import javafx.stage.Stage;

public class MediaPlayerApp extends Application {

    private MediaPlayer mediaPlayer;

    @Override
    public void start(Stage primaryStage) throws Exception {
        primaryStage.setTitle("Media Player");

        Button playButton = new Button("Play");
        playButton.setOnAction(e -> mediaPlayer.play());

        Button stopButton = new Button("Stop");
        stopButton.setOnAction(e -> mediaPlayer.stop());

        BorderPane borderPane = new BorderPane();

        Media media = new Media("http://www.example.com/sample.mp4");
        mediaPlayer = new MediaPlayer(media);
        MediaView mediaView = new MediaView(mediaPlayer);
        borderPane.setCenter(mediaView);
        borderPane.setBottom(stopButton);
        borderPane.setRight(playButton);

        Scene scene = new Scene(borderPane, 600, 400);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}

In this code, we create two buttons: playButton and stopButton . When the play button is clicked, we call the play() method of the mediaPlayer object . When the stop button is clicked, we call the stop() method of the mediaPlayer object . We also create a Media object with the URL of the example video file and a mediaPlayer object with a Media object . Finally, we create a MediaView object with a MediaPlayer object and set it as the center of the BorderPane .

Step 3. Testing the media player

Now that we have the media player UI configured, we can test it by launching the application. When we launch the application, the media player UI should appear and we can click the play button to start playing the video file. We can also click the stop button to stop playing the video file.

Step 4: Setting up your media player

Now that we have a working media player, we can customize it to our liking. We can change the layout of the user interface, change the video file being played, add additional buttons to adjust the volume, or add a progress bar to show the progress of the video.