Java8 flatMap demo 代码直接可以运行

快来打我* 2022-06-13 10:28 191阅读 0赞

参考自:http://www.cnblogs.com/shenlanzhizun/p/6027042.html

package com.by.interfaces;
    
    import java.util.ArrayList;
    import java.util.Arrays;
    import java.util.List;
    import java.util.stream.Collectors;
    
    class Student {
    
        public Student(long id, String name, int age, int grade, String major, String school) {
            this.id = id;
            this.name = name;
            this.age = age;
            this.grade = grade;
            this.major = major;
            this.school = school;
        }
    
        public Student(String name) {
            this.name = name;
        }
    
    
        public Student() {
        }
    
        private List<String> attributes = Arrays.asList("111", "222", "333");
    
        /**
         * 学号
         */
        private long id;
    
        private String name;
    
        private int age;
    
        /**
         * 年级
         */
        private int grade;
    
        /**
         * 专业
         */
        private String major;
    
        /**
         * 学校
         */
        private String school;
    
        public long getId() {
            return id;
        }
    
        public void setId(long id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public int getAge() {
            return age;
        }
    
        public void setAge(int age) {
            this.age = age;
        }
    
        public int getGrade() {
            return grade;
        }
    
        public void setGrade(int grade) {
            this.grade = grade;
        }
    
        public String getMajor() {
            return major;
        }
    
        public void setMajor(String major) {
            this.major = major;
        }
    
        public String getSchool() {
            return school;
        }
    
        public void setSchool(String school) {
            this.school = school;
        }
    
        public List<String> getAttributes() {
            return attributes;
        }
    
        public void setAttributes(List<String> attributes) {
            this.attributes = attributes;
        }
    }
    
    public class Main {
        public static void main(String[] args) {
    
            List<Student> students = new ArrayList<Student>();
    
            students.add(new Student(20160001, "孔明4", 20, 1, "土木工程", "武汉大学"));
            students.add(new Student(20160002, "伯约", 21, 2, "信息安全", "武汉大学"));
            students.add(new Student(20160003, "玄德", 22, 3, "经济管理", "武汉大学"));
            students.add(new Student(20160004, "云长", 21, 2, "信息安全", "武汉大学"));
            students.add(new Student(20161001, "翼德", 21, 2, "机械与自动化", "华中科技大学"));
            students.add(new Student(20161002, "元直", 23, 4, "土木工程", "华中科技大学"));
            students.add(new Student(20161003, "奉孝", 23, 4, "计算机科学", "华中科技大学"));
            students.add(new Student(20162001, "仲谋", 22, 3, "土木工程", "浙江大学"));
            students.add(new Student(20162002, "鲁肃", 23, 4, "计算机科学", "浙江大学"));
            students.add(new Student(20163001, "丁奉", 24, 5, "土木工程", "南京大学"));
    
            //mapToLong的使用demo
            double value = students.stream().filter(student -> "计算机科学".equals(student.getMajor())).mapToLong(aaa -> aaa.getId()).sum();
    
    
            String[] strs = {"java8", "is", "easy", "to", "use"};
    
    
            List<String[]> distinctStrs = Arrays.stream(strs)
                    .map(str -> str.split(""))  // 映射成为Stream<String[]>
                    .distinct()
                    .collect(Collectors.toList());
    
            distinctStrs.forEach(strings -> Arrays.stream(strings).forEach(s -> System.out.println(s)));
    
    
            System.out.println("==================================map方式");
    
            List<String> distinctStrsByFlatMap = Arrays.stream(strs)
                    .map(str -> str.split(""))  // 映射成为Stream<String[]>
                    .flatMap(Arrays::stream)  // 扁平化为Stream<String>
                    .distinct()
                    .collect(Collectors.toList());
    
            distinctStrsByFlatMap.forEach(s -> System.out.println(s));
    
            System.out.println("==================================flatMap的方式");
    
    
            List<List<Student>> studentss = new ArrayList<>();
            studentss.add(students);
            studentss.add(students);
            System.out.println(studentss.size());
    
            System.out.println("经过了flatmap处理后的stream查看下尺寸是多少" + studentss.stream().flatMap(students1 -> students1.stream()).count());
    
            System.out.println(studentss.stream().flatMap(students1 -> students1.stream()).max((o1, o2) -> (o1.getName().length() - o2.getName().length())).get().getName());
    
    
            System.out.println("经过了flatMap进行了彻底的流处理查看下有多少流" + studentss.stream().flatMap(students1 -> students1.stream()).flatMap(student -> student.getAttributes().stream()).count());
    
    
            studentss.stream().flatMap(students1 -> students1.stream()).flatMap(student -> student.getAttributes().stream()).forEach(s -> System.out.println(s));
    
    
            
    
        }
    }