Java Lambda 归约 reduce

Java Lambda 归约 reduce

public class Menu {
	
	
	private String name;
	
	private Double price;
	
	private Double kilo;
	
	private String type;
	
	public Menu() {
		
	}

	public Menu(String name, Double price, Double kilo, String type) {
		super();
		this.name = name;
		this.price = price;
		this.kilo = kilo;
		this.type = type;
	}

	public String getName() {
		return name;
	}

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

	public Double getPrice() {
		return price;
	}

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

	public Double getKilo() {
		return kilo;
	}

	public void setKilo(Double kilo) {
		this.kilo = kilo;
	}

	public String getType() {
		return type;
	}

	public void setType(String type) {
		this.type = type;
	}
	
	
}

Menu pork    = new Menu("猪肉", 9.9, 10.0, "肉类");
Menu beef    = new Menu("牛肉", 38.8, 5.0, "肉类");
Menu chicken = new Menu("鸡肉", 6.5, 30.0, "肉类");
Menu tomato  = new Menu("土豆", 3.5, 30.0, "蔬菜");
Menu potato  = new Menu("西红柿", 7.5, 20.0, "蔬菜");
Menu apple   = new Menu("苹果", 3.5, 20.0, "水果");
Menu orange  = new Menu("橙子", 4.0, 20.0, "水果");
List menuList = Arrays.asList(pork, beef, chicken, tomato, potato, apple, orange);

归约：将流归约成一个值。

double totalPrice = menuList.stream().map(Menu::getPrice).reduce(0.0, (a, b) -> a + b);
System.out.println(totalPrice);

73.69999999999999

double totalPrice = menuList.stream().map(menu -> {return new BigDecimal(menu.getPrice());}).reduce(BigDecimal.ZERO, BigDecimal::add).doublevalue();
System.out.println(totalPrice);

73.7 

归约查找最大值

double maxPrice = menuList.stream().map(Menu::getPrice).reduce(Double::max).get();
System.out.println(maxPrice);

38.8

归约查找最小值

double minPrice = menuList.stream().map(Menu::getPrice).reduce(Double::min).get();
System.out.println(minPrice);

3.5