java8

最新推荐文章于 2025-06-05 00:49:08 发布

weixin_30527423

最新推荐文章于 2025-06-05 00:49:08 发布

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CC 4.0 BY-SA版权

文章标签： java

原文链接：http://www.cnblogs.com/qq1728209643/p/10053055.html

package pers.lan.jc.e;

import org.junit.Test;

import java.util.*;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.function.Predicate;
import java.util.stream.Collectors;

/**
 * @author lan  [1728209643@qq.com]
 * @create 2018-12-02 11:08
 * @desc java lambda和函数式编程
 */
public class Java8 {

    private List<Apple> apples = Arrays.asList(
            Apple.builder().id(0).color("红色").unitPrice(2).weight(3).build(),
            Apple.builder().id(1).color("红色").unitPrice(2).weight(4).build(),
            Apple.builder().id(2).color("绿色").unitPrice(1).weight(2).build(),
            Apple.builder().id(3).color("绿色").unitPrice(1).weight(3).build(),
            Apple.builder().id(4).color("青色").unitPrice(1).weight(4).build(),
            Apple.builder().id(5).color("青色").unitPrice(1).weight(5).build(),
            Apple.builder().id(6).color("黑色").unitPrice(3).weight(5).build(),
            Apple.builder().id(7).color("黑色").unitPrice(3).weight(4).build()
    );

    private Predicate<Apple> redApplePredicate = apple -> "红色".equals(apple.getColor());

    private Predicate<Apple> predicate(String color) {
        return (apple -> color.equals(apple.getColor()));
    }

    /**
     * @desc 获取某种颜色的苹果
     * @author lan [1728209643@qq.com]
     * @create 2018/12/2 11:23
     */
    @Test
    public void testFilter_Predicate() {
        List<Apple> appleList;
        appleList = apples.stream().filter(redApplePredicate).collect(Collectors.toList());
        System.out.println(appleList);

        appleList = apples.stream().filter(predicate("绿色")).collect(Collectors.toList());
        System.out.println(appleList);

        appleList = apples.stream().filter(predicate("青色")).collect(Collectors.toList());
        System.out.println(appleList);

        appleList = apples.stream().filter(apple -> "红色".equals(apple.getColor())).collect(Collectors.toList());
        System.out.println(appleList);
    }

    /**
     * @desc 匹配 anyMatch/allMatch
     * @author lan [1728209643@qq.com]
     * @create 2018/12/2 12:33
     */
    @Test
    public void testMatch() {
        //是否有红色的
        boolean match = apples.stream().anyMatch(predicate("红色"));
        System.out.println(match);


        //是不是所有的都是红色
        match = apples.stream().allMatch(predicate("红色"));
        System.out.println(match);

    }

    /**
     * @desc 查找 findAny/findFirst
     * @author lan [1728209643@qq.com]
     * @create 2018/12/2 12:37
     */
    @Test
    public void testFind() {
        //第一个
        Optional<Apple> first = apples.stream().findFirst();
        System.out.println(first.get());

        //任何一个
        Optional<Apple> any = apples.stream().findAny();
        System.out.println(any.get());

        //查找重量大于4的第一个
        first = apples.stream().filter(apple -> apple.getWeight() > 4).findFirst();
        System.out.println(first.get());
    }

    /**
     * @desc 计算苹果的价格forEach() -> Apple.setTotalPrice()
     * @author lan [1728209643@qq.com]
     * @create 2018/12/2 12:01
     */
    @Test
    public void testConsumer() {
        apples.forEach(apple -> apple.setTotalPrice(apple.getUnitPrice() * apple.getWeight()));
        System.out.println(apples);
    }


    /**
     * @desc 把苹果变成有包装的苹果 Apple -> PackedApple, 可以用于将集合中的元素进行类型转换的操作
     * @author lan [1728209643@qq.com]
     * @create 2018/12/2 11:47
     */
    @Test
    public void testFunction() {
        List<PackedApple> packedApples;

        //把苹果变成有包装的苹果 Apple -> PackedApple
        packedApples = apples.stream().map(
                apple -> PackedApple.builder().apple(apple).packageBy("lan").packageType("礼盒包装").build()).collect(Collectors.toList());
        System.out.println(packedApples);

        packedApples = apples.stream().map(apple -> {
            if ("红色".equals(apple.getColor())) {
                return PackedApple.builder().apple(apple).packageBy("lan").packageType("礼盒包装").build();
            } else if (predicate("青色").test(apple)) {
                return PackedApple.builder().apple(apple).packageBy("小明").packageType("咬一口再包装").build();
            } else {
                return PackedApple.builder().apple(apple).packageBy("小强").packageType("简单包装").build();
            }
        }).collect(Collectors.toList());
        System.out.println(packedApples);

    }

    /**
     * @desc 有哪些颜色/有哪些价格
     * @author lan [1728209643@qq.com]
     * @create 2018/12/2 11:35
     */
    @Test
    public void testDistinct() {
        //所有的颜色
        List<String> colors = apples.stream().map(Apple::getColor).collect(Collectors.toList());
        System.out.println(colors);
        //有哪些颜色...
        colors = apples.stream().map(Apple::getColor).distinct().collect(Collectors.toList());
        System.out.println(colors);

        //有哪些价格
        List<Integer> unitPrices = apples.stream().map(Apple::getUnitPrice).distinct().collect(Collectors.toList());
        System.out.println(unitPrices);
    }

    /**
     * @desc 把颜色的每个字都分开
     * @author lan [1728209643@qq.com]
     * @create 2018/12/2 12:07
     */
    @Test
    public void testFlatMap() {
        List<String> colors = apples.stream().map(apple -> apple.getColor().split("")).flatMap(Arrays::stream).collect(Collectors.toList());
        System.out.println(colors);

        List<String> list = Arrays.asList("Hello World!", "I'm Lan");
        list = list.stream().map(s -> s.split("")).flatMap(Arrays::stream).collect(Collectors.toList());
        System.out.println(list);
        List<Integer[]> integers = Arrays.asList(
                new Integer[]{0, 1, 5, 6},
                new Integer[]{1, 2, 3, 5}
        );
        List<Integer> integerList = integers.stream().flatMap(Arrays::stream).distinct().collect(Collectors.toList());
        System.out.println(integerList);
    }

    /**
     * @desc 计算所有苹果的总价
     * @author lan [1728209643@qq.com]
     * @create 2018/12/2 12:48
     */
    @Test
    public void testReduce() {

        //总价
        AtomicInteger total1 = new AtomicInteger();
        apples.forEach(apple -> total1.addAndGet(apple.getWeight() * apple.getUnitPrice()));
        System.out.println(total1.get());

        //总价
        Integer total = apples.stream().map(apple -> apple.getUnitPrice() * apple.getWeight()).reduce(0, (a, b) -> a + b);
        System.out.println(total);

        //所有苹果的重量
        Integer totalWeight = apples.stream().map(Apple::getWeight).reduce(0, (a, b) -> a + b);
        System.out.println(totalWeight);
    }

    /**
     * @desc max/min
     * @author lan [1728209643@qq.com]
     * @create 2018/12/2 12:57
     */
    @Test
    public void testMax_Min() {
        //总价最高的
        Optional<Apple> optional = apples.stream().max((o1, o2) -> o1.getUnitPrice() * o2.getWeight() - o2.getUnitPrice() * o2.getWeight());
        System.out.println(optional.get());

        //总价最低的
        optional = apples.stream().min((o1, o2) -> o1.getUnitPrice() * o2.getWeight() - o2.getUnitPrice() * o2.getWeight());
        System.out.println(optional.get());

        //重量最大的
        optional = apples.stream().max(Comparator.comparingInt(Apple::getWeight));
        System.out.println(optional.get());
    }

    /**
     * @desc 红色苹果的数量
     * @author lan [1728209643@qq.com]
     * @create 2018/12/2 13:02
     */
    @Test
    public void testCount() {
        long count = apples.stream().filter(predicate("红色")).count();
        System.out.println(count);
    }

    /**
     * @desc collect
     * @author lan [1728209643@qq.com]
     * @create 2018/12/2 13:08
     */
    @Test
    public void test() {
        //list变成map, apple -> <id, apple>
        Map<Integer, Apple> appleMap = apples.stream().collect(Collectors.toMap(Apple::getId, apple -> apple));
        System.out.println(appleMap);

        //按颜色分组, apple -> <color, List<Apple>>
        Map<String, List<Apple>> groupByColor = apples.stream().collect(Collectors.groupingBy(Apple::getColor));
        System.out.println(groupByColor);
    }
}

　　测试所用的Apple类

package pers.lan.jc.e;

import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * @author lan  [1728209643@qq.com]
 * @create 2018-12-02 11:12
 * @desc 你是我眼中的苹果
 */
@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class Apple {

    //id
    private int id;

    //颜色
    private String color;

    //重量
    private int weight;

    //单价
    private int unitPrice;

    //总价
    private int totalPrice;

}

　　PackedApple

package pers.lan.jc.e;

import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * @author lan  [1728209643@qq.com]
 * @create 2018-12-02 11:41
 * @desc 包装过的苹果
 */
@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
public class PackedApple {

    //包装方式
    private String packageType;

    //包装人
    private String packageBy;

    //苹果
    private Apple apple;

}

转载于:https://www.cnblogs.com/qq1728209643/p/10053055.html