JAVA EE: How to use collectingAndThen method of Collectors | Java 8 streams

Wednesday 20 September 2017

How to use collectingAndThen method of Collectors | Java 8 streams | Streams in Java 8

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https://www.youtube.com/watch?v=ZbEq3wAO9MM&list=UUhwKlOVR041tngjerWxVccw

Product.java

public class Product
{
    private String name;
    private int price;

    public Product(String name, int price)
    {
        super();
        this.name = name;
        this.price = price;
    }

    public String getName()
    {
        return name;
    }

    public void setName(String name)
    {
        this.name = name;
    }

    public int getPrice()
    {
        return price;
    }

    public void setPrice(int price)
    {
        this.price = price;
    }

    @Override
    public String toString()
    {
        return "Product [name=" + name + ", price=" + price + "]";
    }

}

StreamDemo.java

import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;

public class StreamDemo
{
    public static void main(String[] args)
    {
        List<Product> productList = Arrays.asList(
                new Product("potatoes", 15),
                new Product("orange", 15), new Product("lemon", 20),
                new Product("bread", 20), new Product("sugar", 30));

        /*
         * Pushing the collector to perform additional transformation:
         * 
         * The collector has converted a stream to a Set and then
         * created the unmodifiable Set out of it.
         */
        Set<Product> unmodifiableSet = productList.stream()
                .collect(Collectors.collectingAndThen(
                        Collectors.toSet(),
                        Collections::unmodifiableSet));

        System.out.println("unmodifiableSet = " + unmodifiableSet);
        
    }

}

Output

unmodifiableSet = [Product [name=orange, price=15], Product [name=lemon, price=20], 
Product [name=potatoes, price=15], Product [name=sugar, price=30], 
Product [name=bread, price=20]]