Java 8 集合的 Streams 使用示例

　　Streams 是 Java 8 集合的新特性

　　import java.util.ArrayList;

　　import java.util.List;

　　import java.util.stream.Stream;

　　public class StreamDemo{

　　public static void main(String args[]) {

　　// Initialization of Collection

　　List orderBook = new ArrayList<>();

　　Order buyGoogle = new Order("GOOG.NS", 300, 900.30, Order.Side.BUY);

　　Order sellGoogle = new Order("GOOG.NS", 600, 890.30, Order.Side.SELL);

　　Order buyApple = new Order("APPL.NS", 400, 552, Order.Side.BUY);

　　Order sellApple = new Order("APPL.NS", 200, 550, Order.Side.SELL);

　　Order buyGS = new Order("GS.NS", 300, 130, Order.Side.BUY);

　　orderBook.add(buyGoogle);

　　orderBook.add(sellGoogle);

　　orderBook.add(buyApple);

　　orderBook.add(sellApple);

　　orderBook.add(buyGS);

　　// Java 8 Streams Example 1 : Filtering Collection elements

　　// Filtering buy and sell order using filter() method of java.util.Stream class

　　Stream stream = orderBook.stream();

　　Stream buyOrders = stream.filter((Order o) -> o.side().equals(Order.Side.BUY));

　　System.out.println("No of Buy Order Placed :" + buyOrders.count());

　　Stream sellOrders = orderBook.stream().filter((Order o) -> o.side() == Order.Side.SELL);

　　System.out.println("No of Sell Order Placed : " + sellOrders.count());

　　// Java 8 Streams Example 2 : Reduce or Fold operation

　　// Calculating total value of all orders

　　double value = orderBook.stream().mapToDouble((Order o) -> o.price()).sum();

　　System.out.println("Total value of all orders : " + value);

　　long quantity = orderBook.stream().mapToLong((Order o) -> o.quantity()).sum();

　　System.out.println("Total quantity of all orders : " + quantity);

　　}

　　}

　　class Order {

　　enum Side {

　　BUY, SELL;

　　}

　　private final String symbol;

　　private final int quantity;

　　private double price;

　　private final Side side;

　　public Order(String symbol, int quantity, double price, Side side) {

　　this.symbol = symbol;

　　this.quantity = quantity;

　　this.price = price;

　　this.side = side;

　　}

　　public double price() {

　　return price;

　　}

　　public void price(double price) {

　　this.price = price;

　　}

　　public String symbol() {

　　return symbol;

　　}

　　public int quantity() {

　　return quantity;

　　}

　　public Side side() {

　　return side;

　　}

　　}

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　　No of Buy Order Placed :3

　　No of Sell Order Placed : 2

　　Total value of all orders : 3022.6

　　Total quantity of all orders : 1800