java8 常用操作案例【经典版】超赞！

news2024/12/27 15:56:45

一案例

1.1 对象转list

1.2 过滤对象

1.3 排序

1.4 匹配

1.5 最大值最小值

1.6 拼接字符串

1.7 求和

1.8 分组

1.9 分组求和

1.10 综合案例

一案例

1.1 对象转list

    /**
    * @author admin
      对象转map ;  mapper层实体类获取,到业务层转换为DTO,
    * @return void
    */
    public static void duixiangToMap(){
        List<User> list = Arrays.asList(
                new User(1L, "张三", 18),
                new User(2L, "李四", 20),
                new User(3L, "王五", 33),
                new User(4L, "赵六", 44));
        List<UserDTO> userDTOList = list.stream().map(obj -> {
            UserDTO userDTO = new UserDTO(obj.getId(), obj.getName(), obj.getAge());
            return userDTO;
        }).collect(Collectors.toList());
        userDTOList.forEach(System.out::println);
    }

结果：

1.2 过滤对象

    /**
    * @author admin
    * @description       
      案例2：  过滤长度大于7
    * @return void
    */
    public static void duiFilter(){
        List<String> list = Arrays.asList(  "SpringBoot",   "SpringCloud", "Spring", "SpringMVC","mybatis","html",  "git"  );        
        List<String> stringList = list.stream().filter(obj -> obj.length() > 7).collect(Collectors.toList());     
        System.out.println(stringList);
    }

1.3 排序

    public static void testSorted(){
        List<String> list = Arrays.asList(
                "SpringBoot",                "SpringCloud",                "Spring",
                "SpringMVC",                "mybatis",                "html",                "git"
        );
        List<String> collect = list.stream().sorted().collect(Collectors.toList());
        System.out.println(collect);
        //根据长度进行排序
        List<String> collect1 = list.stream().sorted(Comparator.comparing(String::length)).collect(Collectors.toList());
        System.out.println(collect1);
        //limit截取
        List<String> collect2 = list.stream().sorted(Comparator.comparing(String::length)).limit(3).collect(Collectors.toList());
        System.out.println(collect2);
        //limit截取
        List<String> collect3 = list.stream().sorted(Comparator.comparing(String::length).reversed()).limit(3).collect(Collectors.toList());
        System.out.println(collect3);
          }

1.4 匹配

          /**
          * @author admin
          * @description       
           match 匹配
          allMatch检查是否匹配所有元素，符合才返回trueanyMatch检查是否至少匹配一个元素
          */
          public static void testAllOrAnyMatch(){
              List<String> list = Arrays.asList(
                      "SpringBoot",
                      "SpringCloud",
                      "Spring",
                      "SpringMVC",
                      "mybatis",
                      "html",
                      "git"
                    );

              boolean allMatch = list.stream().allMatch(obj -> obj.length() > 5);
              System.out.println(allMatch);
              boolean anyMatch = list.stream().anyMatch(obj -> obj.length() > 10);
              System.out.println(anyMatch);
          }

1.5 最大值最小值

    /**
    * @author admin
     求最大值和最小值
    * @return void
    */
    public static void testMaxMin(){
        List<User> list = Arrays.asList(
                new User(1L, "张三", 18),
                new User(2L, "李四", 20),
                new User(3L, "王五", 33),
                new User(4L, "赵六", 44));
        Optional<User> userOptional = list.stream().max(Comparator.comparingInt(User::getAge));
        System.out.println(userOptional.get().getAge());
        Optional<User> userOptional1 = list.stream().min(Comparator.comparingInt(User::getAge));
        System.out.println(userOptional1.get().getAge());
    }

1.6 拼接字符串

/**
拼接字符串
*/
public static void joinStr() {
    String collect = Stream.of("spt", "smvc","111").collect(Collectors.joining("@" ));
    System.out.println("r:"+collect);
}

结果：

1.7 求和

/**
* @author admin
   求和      
* @return void
*/
public static void qiuHe(){
    Integer value = Stream.of(1, 2, 3, 4, 5, 6).reduce((item1,item2) -> item1 + item2).get();
    System.out.println(value);
//不适用lambda表达式
Integer value1 = Stream.of(1, 2, 3, 4, 5, 6).reduce(new BinaryOperator<Integer>() {
    @Override
    public Integer apply(Integer integer, Integer integer2) {
        return integer + integer2;    }}
     ).get();
System.out.println("value1:"+value1);
//10作为初始值，然后和第一个数相加，结果再与第二个数相加，直到所有的数相加完成为止
  Integer value3 = Stream.of(1, 2, 3, 4, 5, 6, 7, 8, 9).reduce(10, (sum, item) -> sum + item);
  System.out.println("value3:"+value3);
}

1.8 分组

public static void   qiuByGroup() {
    List<String> list = Arrays.asList("SpringBoot", "SpringCloud",
            "Spring", "SpringMVC", "mybatis", "html",
            "git");
    Map<Boolean, List<String>> listMap = list.stream().collect(partitioningBy(obj -> obj.length() > 8));
    listMap.forEach((key, value) -> {
        System.out.println(key);
        value.forEach(System.out::println);
        System.out.println();
    });
}

1.9 分组求和

public static void  qiuByGroupSUm(){
    //根据学生的省份进行分组
    List<Student> students = Arrays.asList(new Student("⼴东", 23),        new Student("⼴东", 24),        new Student("⼴东", 23),
            new Student("北京", 22),        new Student("北京", 20),        new Student("北京", 20),        new Student("海南", 25));
    Map<String, List<Student>> collect = students.stream().collect(Collectors.groupingBy(obj -> obj.getName()));
    collect.forEach((key,value)->{    System.out.println(key);    value.forEach(System.out::println);});
    //统计学生的各个年龄信息
    IntSummaryStatistics summaryStatistics = students.stream().collect(Collectors.summarizingInt(Student::getAge));
    System.out.println("平均值："+summaryStatistics.getAverage());
    System.out.println("人数："+summaryStatistics.getCount());
    System.out.println("最大值："+summaryStatistics.getMax());
    System.out.println("最小值："+summaryStatistics.getMin());
    System.out.println("总和："+summaryStatistics.getSum());
}

1.10 综合案例

Java 8 Stream API：强大而灵活的数据处理流水线

public static void testTen(){
//总价 35
         List<VideoOrder> videoOrders1 = Arrays.asList(
        new VideoOrder("20190242812", "springboot教程", 3),
            new VideoOrder("20194350812", "微服务SpringCloud", 5),
            new VideoOrder("20190814232", "Redis教程", 9),
            new VideoOrder("20190523812", "⽹⻚开发教程", 9),
            new VideoOrder("201932324", "百万并发实战Netty", 9));
    //总价 54
    //
    List<VideoOrder> videoOrders2 = Arrays.asList(
            new VideoOrder("2019024285312", "springboot教程", 3),
            new VideoOrder("2019081453232", "Redis教程", 9),
            new VideoOrder("20190522338312", "⽹⻚开发教程", 9),
            new VideoOrder("2019435230812", "Jmeter压⼒测试", 5),
            new VideoOrder("2019323542411", "Git+Jenkins持续集成", 7),
            new VideoOrder("2019323542424", "Idea全套教程", 21));
    //交集
    List<VideoOrder> intersectionList = videoOrders1.stream().filter(videoOrders2::contains).collect(Collectors.toList());
    System.out.println("交集=："+intersectionList);
    //差集1
    List<VideoOrder> diffList1 = videoOrders1.stream().filter(obj -> !videoOrders2.contains(obj)).collect(Collectors.toList());
    System.out.println("差集1="+diffList1);
    //并集
    List<VideoOrder> allVideoOrder = videoOrders1.parallelStream().collect(Collectors.toList());      allVideoOrder.addAll(videoOrders2);
    System.out.println("并集="+allVideoOrder);
    //去重并集
    List<VideoOrder> allVideoOrderDistinct = allVideoOrder.stream().distinct().collect(Collectors.toList());
    System.out.println("去重并集="+allVideoOrderDistinct);
    //两个订单平均价格
    double videoOrderAvg1 = videoOrders1.stream().collect(Collectors.averagingInt(VideoOrder::getMoney));
    System.out.println("订单1平均价格="+videoOrderAvg1);
    double videoOrderAvg2 = videoOrders2.stream().collect(Collectors.averagingInt(VideoOrder::getMoney));
    System.out.println("订单2平均价格="+videoOrderAvg2);
    //两个订单总价格
    long sum1 = videoOrders1.stream().collect(Collectors.summarizingInt(VideoOrder::getMoney)).getSum();
    System.out.println("订单1总价格="+sum1);
    long sum2 = videoOrders2.stream().collect(Collectors.summarizingInt(VideoOrder::getMoney)).getSum();
    System.out.println("订单2总价格="+sum2);
}