Java8 - reduceで検索

Java8のstreamのreduceを使ってカスタムオブジェクト(この例ではItem)の検索をする例．


Item.java

package org.tanuneko;

import java.util.ArrayList;
import java.util.List;
import java.util.function.BinaryOperator;

public class Reducer {

    public static void main( String args[] ) {

        BinaryOperator<Item> costsMore = (m,n)->
                                          { return ( m.getPrice() > n.getPrice() ? m:n ); };

        System.out.println(genItems().stream().reduce(getCheapestOne(), costsMore));
     }

    private static List<Item> genItems() {
        List<Item> items = new ArrayList<>();
        items.add( new Item( 500, "Basket" ) );
        items.add( new Item( 1200, "Rack" ) );
        items.add( new Item( 700, "Small Table" ) );
        items.add( new Item( 50000, "Granite Table" ) );
        items.add( new Item( 15000, "Closet" ) );
        items.add( new Item( 400, "Grout" ) );
        return items;
    }

    private static Item getCheapestOne() {
        return new Item( Integer.MIN_VALUE, "VOID" );
    }
}

Item.java

package org.tanuneko;

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

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

    public int getPrice() { return price; }
    public String getName() { return name; }

    @Override
    public String toString() {
        return "Item{" +
                "price=" + price +
                ", name='" + name + '\'' +
                '}';
    }
}

実行結果
Item{price=50000, name='Granite Table'}