Stream API in Java 8: How to remove duplicate elements from a collection using distinct() method

Stream API in Java 8: How to use the distinct() method to remove duplicate elements in a collection

In Java 8, the Stream API was introduced, which provides a new data processing method, Collection data can be processed more concisely and efficiently. One common operation is to remove duplicate elements from a collection. The Stream API in Java 8 provides the distinct() method to easily implement this function.

First of all, we need to understand the basic usage of Stream API. Stream is a new data type in Java 8, which represents a series of elements and can perform various operations. We can obtain a Stream object by calling the stream() method of the collection, then perform various operations on the Stream object, and finally return the result as a new Stream object or other forms of data. The Stream API provides us with a series of methods for filtering, mapping, sorting, aggregation and other operations.

It is very simple to use the distinct() method to remove duplicate elements in a collection. We only need to convert the collection into a Stream object and then call the distinct() method. The distinct() method returns a new Stream object, which contains the deduplicated elements in the original Stream object.

The following is a sample code that demonstrates how to use the distinct() method to remove duplicate elements in a collection:

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class DistinctExample {
    public static void main(String[] args) {

        List<Integer> numbers = new ArrayList<>();
        numbers.add(1);
        numbers.add(2);
        numbers.add(3);
        numbers.add(1);
        numbers.add(2);
        numbers.add(3);

        System.out.println("原始集合：" + numbers);

        List<Integer> distinctNumbers = numbers.stream()
                                               .distinct()
                                               .collect(Collectors.toList());

        System.out.println("去重后的集合：" + distinctNumbers);
    }
}

In the above example, we created a List collection containing duplicate elements . Then, we convert it into a Stream object by calling the stream() method of the numbers collection. Next, we call the distinct() method to remove duplicate elements, and convert the result into a new List collection through collect(Collectors.toList()).

Run the above code, we can get the following output:

Original set: [1, 2, 3, 1, 2, 3]
After deduplication: [ 1, 2, 3]

As you can see, the distinct() method is used to successfully remove duplicate elements from the collection.

It should be noted that the distinct() method will remove duplicates based on the equals() method of the element. If the elements in the collection are custom objects, then we need to ensure that the object implements the equals() method correctly.

In addition, the distinct() method can also be used to deduplicate objects. Just implement the equals() method correctly in the object class.

To summarize, the Stream API in Java 8 provides a concise and efficient way to remove duplicate elements from a collection. We can easily implement this function by calling the distinct() method. Using the Stream API can reduce tedious code and improve code readability and maintainability. If you haven't tried the Stream API in Java 8, now is the time to learn and apply it!

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