JAVA EE: How to find the sum of all the product price using reduce method of Java 8 Stream

Wednesday 12 July 2017

How to find the sum of all the product price using reduce method of Java 8 Stream

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Product.java

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

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

    public int getId()
    {
        return id;
    }

    public void setId(int id)
    {
        this.id = id;
    }

    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 [id=" + id + ", name=" + name + ", price="
                + price + "]";
    }

}

StreamDemo.java

import java.util.ArrayList;
import java.util.List;

public class StreamDemo
{
    public static void main(String[] args)
    {
        List<Product> productList = new ArrayList<Product>();

        // Adding Products
        productList.add(new Product(1, "Sony mobile", 25000));
        productList.add(new Product(2, "Lenovo mobile", 15000));
        productList.add(new Product(3, "Nokia mobile", 10000));
        productList.add(new Product(4, "Samsung mobile", 40000));

        
        /*
         * reduce method takes a sequence of input elements 
         * and combines them into a single summary result 
         * by repeated operation.
         * 
         * Using reduce method we can perform Sum, min, max, average, 
         * and string concatenation.
         * 
         * Here we are using reduce() method, which is used to sum of 
         * all the product prices.
         */     
        Integer totalPrice1 = productList.stream() 
                .map(product->product.getPrice())  
                .reduce(0,(sum, price)->sum+price);  // accumulating price  
    
        System.out.println(totalPrice1);  
                
        Integer totalPrice2 = productList.stream()  
                .map(product->product.getPrice())  
                .reduce(0,Integer::sum);   // accumulating price, by referring method of Integer class
        
        System.out.println(totalPrice2);        
    }

}