Stream编程 - 案例总结

红太狼 2023-06-13 09:44 5阅读 0赞

随机数

List<Integer> collect = ThreadLocalRandom.current()
      .ints(0,9)
      .limit(10)
      .boxed()
      .collect(Collectors.toList());
    System.out.println(collect);

获取数组最小的值

int[] nums = new int[]{ 7,3,4,5};
    int value = IntStream.of(nums)
      .min()
      .getAsInt();
    System.out.println(value);

并行方式

int[] nums = new int[]{ 7,3,4,5};
    int value = IntStream.of(nums)
      .parallel()
      .min()
      .getAsInt();
    System.out.println(value);

数组转换

int[] nums = new int[]{ 7,3,4,5};
    List<String> strings = Arrays.stream(nums)
      .boxed()
      .map(Object::toString)
      .collect(Collectors.toList());
    System.out.println(strings);

并发处理，同步返回

List<String> strings = Arrays.asList("www.baidu.com", "1s.app");
    List<String> collect = strings.parallelStream()
      .map(source -> { 
        // 耗时操作
        return "http://" + source;
      }).filter(Objects::nonNull)
      .collect(Collectors.toList());
    System.out.println(collect);

数组只取一项目

String value = Stream.of("www.baidu.com", "1.app")
      .map(s -> { 
        if (s.endsWith("app")){ 
          return s;
        }
        return null;
      })
      .filter(Objects::nonNull)
      .findFirst()
      .orElseThrow(() -> new Exception("未找到"));
    
    System.out.println(value);

去重

`@Data` 提供类所有属性的 get 和 set 方法，此外还提供了equals、canEqual、hashCode、toString 方法。

不懂 Lombok可以查看 \[Lombok 的使用\](Lombok 的使用.md)

@Data
    @AllArgsConstructor
    public static class Person{ 
      private String name;
      private int age;
    }

List<Person> collect = Stream.of(
      new Person("张三", 13),
      new Person("小红", 15),
      new Person("张三", 13))
      .distinct()
      .collect(Collectors.toList());
    System.out.println(collect);

分组

@Data
    @AllArgsConstructor
    public static class Student{ 
      // 班级
      private String cls;
      // 姓名
      private String name;
    }

List<Student> students = Arrays.asList(
            new Student("一年级", "张三"),
            new Student("一年级", "李四"),
            new Student("二年级", "小红")
    );
    Map<String, List<Student>> collect = students.stream()
      .collect(Collectors.groupingBy(Student::getCls));
    
    //查看
    Set<String> clsSets = collect.keySet();
    for(String key : clsSets){ 
      System.out.println("班级：" + key);
      List<Student> list = collect.get(key);
      System.out.println("学生：" + list);
    }

数组合并，并去重

List<String> names1 = Arrays.asList("小明", "小红", "小花");
    List<String> names2 = Arrays.asList("小明","小刘", "小珂", "小张");
    List<String> collect = Stream.concat(names1.stream(), names2.stream())
      .distinct()
      .collect(Collectors.toList());
    // [小明, 小红, 小花, 小刘, 小珂, 小张]
    System.out.println(collect);