1、stream()后可调函数

方法名	说明
filter()	过滤掉一部分元素，剩下符合条件的元素
limit()	取前几个元素，括号里填数字
map()	取实体类里的字段数据
reduce()	归约操作可以将流中元素反复结合起来，得到一个值

2、举例说明

实体类Phone

public class Phone {

    //品牌
    private String brand;

    //价格
    private Integer price;

    public Phone() {
    }

    public Phone(String brand, Integer price) {
        this.brand = brand;
        this.price = price;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public Integer getPrice() {
        return price;
    }

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

测试类TestStream

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class TestStream {

    public static void main(String[] args) {

        Phone phone1 = new Phone("OPPO",2999);
        Phone phone2 = new Phone("VIVO",2599);
        Phone phone3 = new Phone("华为",4999);
        Phone phone4 = new Phone("小米",1999);
        Phone phone5 = new Phone("魅族",2399);

        List<Phone> phoneList = new ArrayList<>();
        phoneList.add(phone1);
        phoneList.add(phone2);
        phoneList.add(phone3);
        phoneList.add(phone4);
        phoneList.add(phone5);

//        //验证filter()，筛选手机价格大于2600的手机，输出OPPO，华为
//        phoneList = phoneList.stream().filter(p -> p.getPrice() > 2600).collect(Collectors.toList());

//        //验证limit(),截取前3条数据，输出OPPO，VIVO，华为
//        phoneList = phoneList.stream().limit(3).collect(Collectors.toList());

//        //验证filter()，limit()连用，输出OPPO，VIVO
//        phoneList = phoneList.stream().filter(p -> p.getPrice() > 2000).limit(2).collect(Collectors.toList());

//        //验证map取实体里字段值，输出2999，2599，4999，1999，2399  (下面是两种用法，结果相同)
//        List<Integer> priceList = phoneList.stream().map(p -> p.getPrice()).collect(Collectors.toList());
//        List<Integer> priceList = phoneList.stream().map(Phone::getPrice).collect(Collectors.toList());
//        priceList.forEach(p -> System.out.println(p));

//        //验证reduce()，求价格总和，输出14995，orElse是当list里没有元素时，输出0
//        Integer totalPrice = phoneList.stream().map(Phone::getPrice).reduce((a, b) -> a + b).orElse(0);
//        System.out.println(totalPrice);



        phoneList.forEach(p -> System.out.println(p.getBrand()));

    }

}