Java1.8特性之Stream流操作

        1、java1.8的集合/数组的Stream操作和函数式编程。

        2、Stream（流）创建。

                a、集合.stream()。

                b、Arrays.stream(数组)

                c、Stream.of(元素1，元素2。。。元素n)

        3、流操作代码：

        实体类 SeniorStudent

@Data
@AllArgsConstructor
@NoArgsConstructor
@Component
@ApiModel(description = "学生信息")
public class SeniorStudent {

    private String name;
    private Integer age;
    private Integer mathScore;
    private Integer chineseScore;

}

        List<SeniorStudent> studentList = new ArrayList();
        studentList.add(new SeniorStudent("lilei",18,89,67));
        studentList.add(new SeniorStudent("hanmeimei",20,34,98));
        studentList.add(new SeniorStudent("zhangsan",18,90,29));
        studentList.add(new SeniorStudent("lisi",22,76,87));

        // 将对象的一个字段做key,然后对象值作为value，组装成一个Map
        Map<String, SeniorStudent> collectMap = studentList.stream().collect(
                Collectors.toMap(SeniorStudent::getName, s -> new SeniorStudent() {{
                    setName(s.getName());
                    setAge(s.getAge());
                    setChineseScore(s.getChineseScore());
                    setMathScore(s.getMathScore());
                }}));
        System.out.println(collectMap);

        // filter 过滤器返回 Stream 然后准换成 SeniorStudent 集合
        System.out.println(studentList.stream().filter(s -> s.getMathScore() > 85).collect(Collectors.toList()));
        System.out.println(studentList.stream().filter(s -> s.getMathScore() > 85 && s.getChineseScore() < 60).collect(Collectors.toList()));
        System.out.println(studentList.stream().filter(s -> s.getMathScore() + s.getChineseScore() > 160).collect(Collectors.toSet()));
        // count 统计数量
        System.out.println(studentList.stream().count());
        // limit 取前几个值
        studentList.stream().limit(2).forEach(System.out::println);
        // skip 跳过前几个
        studentList.stream().skip(2).forEach(System.out::println);
        // distinct 去重
        studentList.add(new SeniorStudent("lisi",22,76,87));
        System.out.println(studentList.stream().count());
        studentList.stream().distinct().forEach(System.out::println);
        // map 映射属性，可以对每个属性操作
        studentList.stream().map(s -> {
            s.setAge(s.getAge()+1);
            return s;
        }).forEach(System.out::println);
        System.out.println();
        // sort 正序
        studentList.stream().sorted( (a,b) -> {
            return a.getChineseScore().compareTo(b.getChineseScore());
        }).forEach(System.out::println);
        System.out.println();
        // sort 反序
        studentList.stream().sorted( (a,b) -> {
            return b.getChineseScore().compareTo(a.getChineseScore());
        }).forEach(System.out::println);
        System.out.println();
        // 获取第一个
        System.out.println(studentList.stream().findFirst().get());
        System.out.println();
        // stream 的 findAny方法获取的是第一条，stream的paralle的findAny是随机获取一个
        System.out.println(studentList.stream().findAny().get());
        System.out.println(studentList.stream().parallel().findAny().get());
        System.out.println();
        // anyMatch 任何一个元素符合条件，allMatch 所有元素都符合条件，noneMatch 没有元素符合条件
        System.out.println(studentList.stream().anyMatch(s -> s.getName().equals("lilei")));
        System.out.println(studentList.stream().allMatch(s -> s.getName().equals("lilei")));
        System.out.println(studentList.stream().noneMatch(s -> s.getName().equals("lilei")));
        System.out.println();
        // max min 元素中某个属性最大和最小的
        System.out.println(studentList.stream().max((a,b) -> a.getChineseScore().compareTo(b.getChineseScore())).get());
        System.out.println(studentList.stream().min((a,b) -> a.getChineseScore().compareTo(b.getChineseScore())).get());
        System.out.println(studentList.stream().max((a,b) -> b.getChineseScore().compareTo(a.getChineseScore())).get());
        System.out.println();
        // 对集合中某个元素的属性进行统计
        System.out.println(studentList.stream().collect(Collectors.summarizingInt(SeniorStudent::getChineseScore)));
        System.out.println(studentList.stream().collect(Collectors.summarizingInt(SeniorStudent::getChineseScore)).getCount());
        System.out.println(studentList.stream().collect(Collectors.summarizingInt(SeniorStudent::getChineseScore)).getSum());
        System.out.println(studentList.stream().collect(Collectors.summarizingInt(SeniorStudent::getChineseScore)).getMax());
        System.out.println(studentList.stream().collect(Collectors.summarizingInt(SeniorStudent::getChineseScore)).getMin());
        System.out.println(studentList.stream().collect(Collectors.summarizingInt(SeniorStudent::getChineseScore)).getAverage());